HomeMy WebLinkAbout03-14-2017 Item 1, KallenPolicyAnalysis
EXECUTIVE SUMMARY
Angela Dills is the Gimelstob-Landry Distinguished Professor of Regional Economic Development at Western Carolina University. Sietse Goffard is a
director’s analyst at the Consumer Financial Protection Bureau and a researcher in the Department of Economics at Harvard University. Jeffrey Miron
is director of economic studies at the Cato Institute and director of undergraduate studies in the Department of Economics at Harvard University.
The views expressed in this paper do not necessarily represent the views of the Consumer Financial Protection Bureau or the federal government.
I n November 2012 voters in the states of Colorado
and Washington approved ballot initiatives that
legalized marijuana for recreational use. Two years
later, Alaska and Oregon followed suit. As many
as 11 other states may consider similar measures in
November 2016, through either ballot initiative or legisla-
tive action.
Supporters and opponents of such initiatives make
numerous claims about state-level marijuana legalization.
Advocates think legalization reduces crime, raises tax
revenue, lowers criminal justice expenditures, improves
public health, bolsters traffic safety, and stimulates the
economy. Critics argue that legalization spurs marijuana
and other drug or alcohol use, increases crime, diminishes
traffic safety, harms public health, and lowers teen educa-
tional achievement. Systematic evaluation of these claims,
however, has been largely absent.
This paper assesses recent marijuana legalizations and
related policies in Colorado, Washington, Oregon, and
Alaska.
Our conclusion is that state marijuana legalizations have
had minimal effect on marijuana use and related outcomes.
We cannot rule out small effects of legalization, and insuffi-
cient time has elapsed since the four initial legalizations to
allow strong inference. On the basis of available data, how-
ever, we find little support for the stronger claims made by
either opponents or advocates of legalization. The absence
of significant adverse consequences is especially striking
given the sometimes dire predictions made by legalization
opponents.
September 16, 2016 | Number 799
Dose of Reality
The Effect of State Marijuana Legalizations
By Angela Dills, Sietse Goffard, and Jeffrey Miron
2“The absence of significant adverse consequences is especially striking given the sometimes dire predictions made by legalization opponents.”
INTRODUCTION
In November 2012 the states of Colorado
and Washington approved ballot initiatives
that legalized marijuana for recreational use
under state law. Two years later, Alaska and
Oregon followed suit.1 In November 2016 as
many as 11 other states will likely consider sim-
ilar measures, through either ballot initiative
or state legislative action.2
Supporters and critics make numerous
claims about the effects of state-level marijuana
legalization. Advocates think that legalization
reduces crime, raises revenue, lowers criminal
justice expenditure, improves public health,
improves traffic safety, and stimulates the econ-
omy.3 Critics argue that legalization spurs mari-
juana and other drug or alcohol use, increases
crime, diminishes traffic safety, harms public
health, and lowers teen educational achieve-
ment.4 Systematic evaluation of those claims
after legalization, however, has been limited,
particularly for Oregon and Alaska.5
This paper assesses the effect to date of
marijuana legalization and related policies in
Colorado, Washington, Oregon, and Alaska.
Each of those four legalizations occurred re-
cently, and each rolled out gradually over sever-
al years. The data available for before and after
comparisons are therefore limited, so our as-
sessments of legalization’s effect are tentative.
Yet some post-legalization data are available,
and considerable data exist regarding earlier
marijuana policy changes—such as legaliza-
tion for medical purposes—that plausibly have
similar effects. Thus available information pro-
vides a useful if incomplete perspective on what
other states should expect from legalization or
related policies. Going forward, additional data
may allow stronger conclusions.
Our analysis compares the pre- and post-
policy-change paths of marijuana use, other
drug or alcohol use, marijuana prices, crime,
traffic accidents, teen educational outcomes,
public health, tax revenues, criminal justice
expenditures, and economic outcomes. These
comparisons indicate whether the outcomes
display obvious changes in trend around the
time of changes in marijuana policy.
Our conclusion is that state-level marijuana
legalizations to date have been associated with,
at most, modest changes in marijuana use and
related outcomes. Our estimates cannot rule out
small changes, and related literature finds some
effects from earlier marijuana policy changes
such as medicalization. But the strong claims
about legalization made by both opponents and
supporters are not apparent in the data. The
absence of significant adverse consequences is
especially striking given the sometimes dire pre-
dictions made by legalization opponents.
The remainder of the paper proceeds as
follows. The next section outlines the recent
changes in marijuana policy in the four states
of interest and discusses the timing of those
changes. Subsequent sections examine the be-
havior of marijuana use and related outcomes
before and after those policy changes. A final
section summarizes and discusses implications
for upcoming legalization debates.
HISTORY OF STATE-LEVEL MARIJUANA LEGALIZATIONS
Until 1913 marijuana was legal throughout
the United States under both state and fed-
eral law.6 Beginning with California in 1913
and Utah in 1914, however, states began out-
lawing marijuana, and by 1930, 30 states had
adopted marijuana prohibition.7 Those state-
level prohibitions stemmed largely from anti-
immigrant sentiment and in particular racial
prejudice against Mexican migrant workers,
who were often associated with use of the
drug. Prohibition advocates attributed ter-
rible crimes to marijuana and the Mexicans
who smoked it, creating a stigma around mari-
juana and its purported “vices.”8 Meanwhile,
film productions like Reefer Madness (1936)
presented marijuana as “Public Enemy Num-
ber One” and suggested that its consumption
could lead to insanity, death, and even homi-
cidal tendencies.9
Starting in 1930, the Federal Bureau of Nar-
cotics pushed states to adopt the Uniform State
Narcotic Act and to enact their own measures
to control marijuana distribution.10 Following
3“Individual states have been backing away from marijuana prohibition since the 1970s.”
the model of the National Firearms Act, in 1937
Congress passed the Marijuana Tax Act, which
effectively outlawed marijuana under federal
law by imposing a prohibitive tax; even strict-
er federal laws followed thereafter.11 The 1952
Boggs Act and 1956 Narcotics Control Act es-
tablished mandatory sentences for drug-related
violations; a first-time offense for marijuana
possession carried a minimum sentence of 2 to
10 years in prison and a fine of up to $20,000.12
Those mandatory sentences were mostly re-
pealed in the early 1970s but reinstated by the
Anti-Drug Abuse Act under President Ronald
Reagan. The current controlling federal legis-
lation is the Controlled Substances Act, which
classifies marijuana as Schedule I. This cat-
egory is for drugs that, according to the Drug
Enforcement Administration (DEA), have “no
currently accepted medical use and a high po-
tential for abuse” as well as a risk of “potentially
severe psychological or physical dependence.”13
Despite this history of increasing federal
action against marijuana (and other drugs),
individual states have been backing away from
marijuana prohibition since the 1970s. Be-
ginning with Oregon 11 states14 decriminal-
ized possession or use of limited amounts of
marijuana between 1973 and 1978.15 A second
wave of decriminalization began with Nevada
in 2001; nine more states and the District of
Columbia have since joined the list.16 Fully 25
states and the District of Columbia have gone
further by legalizing marijuana for medical
purposes. In some states, these medical re-
gimes approximate de facto legalization.
The most dramatic cases of undoing state
prohibitions and departing from federal poli-
cy have occurred in the four states (Colorado,
Washington, Oregon, and Alaska) that have
legalized marijuana for recreational as well as
medical purposes. We next examine these four
states in detail.
Colorado
In 1975 Colorado became one of the first
states to decriminalize marijuana after a land-
mark report by the presidentially appointed
Shafer Commission recommended lower pen-
alties against marijuana use and suggested al-
ternative methods to discourage heavy drug
use. Decriminalization made possessing less
than an ounce of marijuana a petty offense with
a $100 fine.
In November 2000 Colorado legalized
medical marijuana through a statewide ballot
initiative. The proposal, known as Amendment
20 or the Medical Use of Marijuana Act, passed
with 54 percent voter support. It authorized
patients and their primary caregivers to pos-
sess up to two ounces of marijuana and up to six
marijuana plants. Patients also needed a state-
issued Medical Marijuana Registry Identifica-
tion Card with a doctor’s recommendation.
State regulations limited caregivers to prescrib-
ing medical marijuana to no more than five pa-
tients each.
The number of licensed medical marijuana
patients initially grew at a modest rate. Then,
in 2009, after Colorado’s Board of Health aban-
doned the caregiver-to-patient ratio rule, the
medical marijuana industry took off.17 That
same year, in the so-called “Ogden Memo,”18
the U.S. Department of Justice signaled it
would shift resources away from state medical
marijuana issues and refrain from targeting pa-
tients and caregivers.19 Thus, although medical
marijuana remained prohibited under federal
law, the federal government would tend not to
intervene in states where it was legal. Within
months, medical marijuana dispensaries pro-
liferated. Licensed patients rose from 4,800 in
2008 to 41,000 in 2009. More than 900 dispen-
saries operated by the end of 2009, according to
law enforcement.20
In fall 2006 Colorado voters considered
Amendment 44, a statewide ballot initiative
to legalize the recreational possession of up
to one ounce of marijuana by individuals aged
21 or older. Amendment 44 failed, with 58 per-
cent of voters opposed.
In November 2012, however, Colorado voters
passed Amendment 64 with 55 percent support,
becoming one of the first two states to relegal-
ize recreational marijuana. The ballot initiative
authorized individuals aged 21 and older with
valid government identification to grow up to six
4“In November 2012 Wash-ington joined Colorado in legalizing recreational marijuana.”
plants and to purchase, possess, and use up to one
ounce of marijuana.21 Colorado residents could
now buy up to one ounce of marijuana in a single
transaction, whereas out-of-state residents could
purchase 0.25 ounces.22
In light of Amendment 64, Colorado’s gov-
ernment passed new regulations and taxes to
prepare for legalized recreational marijuana use.
A ballot referendum dubbed Proposition AA
that was passed in November 2013 imposed a
15 percent tax on sales of recreational marijuana
from cultivators to retailers and a 10 percent tax
on retail sales (in addition to the existing 2.9 per-
cent state sales tax on all goods). Local govern-
ments in Colorado were permitted to impose
additional taxes on retail marijuana.23
Following about a year of planning, Colo-
rado’s first retail marijuana businesses opened
on January 1, 2014. Each business was required
to pay licensing fees of several hundred dollars
and adhere to other requirements.
Washington
In 1971 Washington’s legislature began loos-
ening its marijuana laws and decreed that pos-
session of less than 40 grams would be charged
as a misdemeanor. The state legalized medical
marijuana in 1998 after a 1995 court case in-
volving a terminal cancer patient being treated
with marijuana brought extra attention to the
issue and set the stage for a citizen-driven bal-
lot initiative. In November 1998 state voters
approved Initiative 692, known as the Wash-
ington State Medical Use of Marijuana Act,
with 59 percent in favor. Use, possession, sale,
and cultivation of marijuana became legal un-
der state law for patients with certain medical
conditions that had been verified by a licensed
medical professional. Initiative 692 also im-
posed dosage limits on the drug’s use. By 2009
an estimated 35,500 Washingtonians had pre-
scriptions to buy medical marijuana legally.
In November 2012 Washington joined Colo-
rado in legalizing recreational marijuana. Vot-
ers passed ballot Initiative 502 with 56 percent
in support amid an 81 percent voter turnout
at the polls. The proposal removed most state
prohibitions on marijuana manufacture and
commerce, permitted limited marijuana use for
adults aged 21 and over, and established the need
for a licensing and regulatory framework to gov-
ern the state’s marijuana industry. Initiative 502
further imposed a 25 percent excise tax levied
three times (on marijuana producers, processors,
and retailers) and earmarked the revenue for
research, education, healthcare, and substance-
abuse prevention, among other purposes.24
Legal possession of marijuana took effect on
December 6, 2012. A year and a half later, Wash-
ington’s licensing board began accepting appli-
cations for recreational marijuana shops. After
some backlog, the first four retail stores opened
on July 8, 2014. As of June 2016, several hundred
retail stores were open across the state.
Oregon
In October 1973 Oregon became the first
state to decriminalize marijuana upon passage
of the Oregon Decriminalization Bill. The bill
eliminated criminal penalties for possession of
up to an ounce of marijuana and downgraded the
offense from a “crime” to a “violation” with a fine
of $500 to $1,000.25 State law continued to out-
law using marijuana in public, growing or selling
marijuana, and driving under the influence. In
1997, state lawmakers attempted to recriminalize
marijuana and restore jail sentences as punish-
ment for possessing less than one ounce, and Or-
egon’s governor signed the bill. Activists gathered
swiftly against the new law, however, and forced a
referendum; the attempt to recriminalize ended
up failing by a margin of 2 to 1.26
Oregon medicalized marijuana by ballot
initiative in November 1998, with 55 percent
support. The Oregon Medical Marijuana Act
legalized cultivation, possession, and use of
marijuana by prescription for patients with spe-
cific medical conditions.27 A new organization
was set up to register patients and caregivers. In
2004 voters turned down a ballot proposal to
increase to 6 pounds the amount of marijuana
a patient could legally possess. Six years later,
voters also rejected an effort to permit medi-
cal marijuana dispensaries, but the state legis-
lature legalized them in 2013.28 As of July 2016,
Oregon’s medical marijuana program counted
5“As of June 2016, Oregon had 426 locations where consumers could legally purchase recreational marijuana.”
nearly 67,000 registered patients, the vast ma-
jority claiming to suffer severe pain, persistent
muscle spasms, and nausea.29
Recreational marijuana suffered several de-
feats before eventual approval. In 1986 the Or-
egon Marijuana Legalization for Personal Use
initiative failed with 74 percent of voters op-
posed.30 In November 2012, a similar measure
also failed, even as neighboring Washington
passed its own legalization initiative. Oregon
Ballot Measure 80 would have allowed personal
marijuana cultivation and use without a license,
plus unlimited possession for those over age 21.
To oversee the new market, the measure would
have established an industry-dominated board
to regulate the sale of commercial marijuana.
This proposal failed with more than 53 percent
of the electorate voting against it.31
Full legalization in Oregon finally passed
on November 4, 2014, when voters approved
Measure 91, officially known as the Oregon
Legalized Marijuana Initiative. This measure
legalized recreational marijuana for individu-
als over age 21 and permitted possession of up
to eight ounces of dried marijuana, along with
four plants, with the Oregon Liquor Con-
trol Commission regulating sales of the drug.
More than 56 percent of voters cast ballots
in favor of the initiative, making Oregon the
third state in the nation (along with Alaska) to
legalize recreational marijuana.32
Oregon’s legislature then adopted several
laws to regulate the marijuana industry. Leg-
islators passed a 17 percent state sales tax on
marijuana retail sales and empowered local
jurisdictions to charge their own additional 3
percent sales tax.33 Later, the state legislature
gave individual counties the option to ban
marijuana sales if at least 55 percent of voters
in those counties opposed Measure 91.34
Legal sales went into effect on October 1,
2015. As of June 2016, Oregon had 426 loca-
tions where consumers could legally purchase
recreational marijuana.35
Alaska
Alaska’s debate over marijuana policy be-
gan with a 1972 court case. Irwin Ravin, an at-
torney, was pulled over for a broken taillight
and found to be in possession of marijuana.
Ravin refused to sign the traffic ticket while he
was in possession of marijuana so that he could
challenge the law. Ultimately, the Alaska Su-
preme Court deemed marijuana possession in
the privacy of one’s home to be constitution-
ally protected, and Ravin v. State established
legal precedent in Alaska for years to come.36
Alaska’s legislature decriminalized mari-
juana in 1975, two years after Oregon. Persons
possessing less than one ounce in public—or
any amount in one’s own home—could be fined
no more than $100, a fine eliminated in 1982.
Marijuana opponents, however, mobilized lat-
er in the decade as law enforcement busted a
number of large, illegal cultivation sites hidden
in residences. A voter initiative in November
1990 proposed to ban possession and use of
marijuana even in one’s own home, punishable
by 90 days of jail time and a $1,000 fine. The
initiative passed with 54 percent support.37
In 1998 Alaska citizens spearheaded an
initiative to legalize medical marijuana, and
69 percent of voters supported it. Registered
patients consuming marijuana for health con-
ditions certified by a doctor could possess up
to one ounce of marijuana or up to six plants.38
Advocates then turned to recreational le-
galization. A ballot initiative in 2000 proposed
legalizing use for anyone 18 years and older and
regulating the drug “like an alcoholic bever-
age.” The initiative failed, with 59 percent of
voters opposed. Voters considered a similar
ballot measure in 2004 but again rejected it.
A third ballot initiative on recreational
marijuana legalization passed in November
2014 with 53 percent of voters in support.
It permitted adults aged 21 and over to pos-
sess, use, and grow marijuana. It also legalized
manufacture and sale. The law further created
a Marijuana Control Board to regulate the in-
dustry and establish excise taxes.
State regulators had originally planned to
start issuing applications to growers, proces-
sors, and stores in early to mid-2016. At the
time of this writing, retail marijuana shops are
not yet open. This delay, along with data limi-
6“Our analysis examines whether the trends in marijuana use and related outcomes changed substantially after these dates.”
tations, makes it difficult to evaluate post-legal-
ization outcomes in Alaska.
KEY DATES
To determine the effect of marijuana legal-
ization and similar policies on marijuana use
and related outcomes, we examine the trends
in use and outcomes before and after key pol-
icy changes. We focus mostly on recreational
marijuana legalizations, because earlier work
has covered other modifications of marijuana
policy such as medicalization.39 The specific
dates we consider, derived from the discussion
above, are as follows:
Colorado
■2001, after legalization of medical mari-
juana
■2009, after liberalization of the medical
marijuana law
■2012, after legalization of recreational
marijuana
■2014, after the first retail stores opened
under state-level legalization
Washington
■1998, after legalization of medical mari-
juana
■2012, after legalization of recreational
marijuana
■2014, after the first retail stores opened
under state-level legalization
Oregon
■1998, after legalization of medical mari-
juana
■2013, after the state legislature legalized
medical marijuana dispensaries
■2014, after legalization of recreational
marijuana
■2015, after the first retail stores opened
under state-level legalization
Alaska
■1990, after voters recriminalized marijuana
■1998, after legalization of medical mari-
juana
■2014, after legalization of recreational
marijuana
Our analysis examines whether the trends
in marijuana use and related outcomes changed
substantially after these dates. Observed chang-
es do not necessarily implicate marijuana policy
because other factors might have changed as
well. Similarly, the absence of changes does not
prove that policy changes had no effect; the
abundance of potentially confounding variables
makes it possible that, by coincidence, a policy
change was approximately offset by some oth-
er factor operating in the opposite direction.
Thus, our analysis focuses on the factual out-
comes of marijuana legalization, rather than on
causal inferences.
DRUG USE
Arguably the most important potential ef-
fect of marijuana legalization is on marijuana
use or other drug or alcohol use. Opinions dif-
fer on whether increased use is problematic or
desirable, but because other outcomes depend
on use, a key step is to determine how much
policy affects use. If such effects are small, then
other effects of legalization are also likely to be
small.
Figure 1 shows past-year use rates in Colo-
rado for marijuana and cocaine, along with
past-month use rates for alcohol.40 The key
fact is that marijuana use rates were increasing
modestly for several years before 2009, when
medical marijuana became readily available in
dispensaries, and continued this upward trend
through legalization in 2012. Post-legalization
use rates deviate from this overall trend, but
only to a minor degree. The data do not show
dramatic changes in use rates corresponding
to either the expansion of medical marijuana
or legalization. Similarly, cocaine exhibits a
mild downward trend over the time period
but shows no obvious change after marijuana
policy changes. Alcohol use shows a pattern
similar to marijuana: a gradual upward trend
but no obvious evidence of a response to mari-
juana policy.
7“The limited available data for Colorado and Alaska show no obvious effect of legalization on youth marijuana use.”
Figure 2 graphs the same variables in Wash-
ington State. As in Colorado, marijuana, co-
caine, and alcohol use proceed along preexist-
ing trends after changes in marijuana policy.
Figure 3 presents analogous data for Ore-
gon.41 Legalization only took effect in 2015 (i.e.,
after the end of currently available substance
use data), inhibiting any measurement of the
effect of policy on data observed thus far. How-
ever, as in other legalizing states, past-year mar-
ijuana use has been rising since the mid-2000s.
Figure 4 presents data on current (past-
month) marijuana use by youth from the Youth
Risk Behavior Survey, a survey of health be-
haviors conducted in middle schools and high
schools. Data are unfortunately unavailable for
Washington and Oregon. The limited available
data for Colorado and Alaska show no obvious
effect of legalization on youth marijuana use.
All those observed patterns in marijuana use
might provide evidence for a cultural explanation
behind legalization: as marijuana becomes more
commonplace and less stigmatized, residents and
legislators become less opposed to legalization.
In essence, rising marijuana use may not be a con-
sequence of legalization, but a cause of it.
Consistent with this possibility, Figure 5 plots,
for all four legalizing states, data on perceptions of
“great risk” from smoking marijuana monthly.42
All four states exhibit a steady downward trend,
indicating that fewer people associate monthly
marijuana use with high risk. These downward
trends predate legalization, consistent with the
view that changing attitudes toward marijuana
fostered both policy changes and increasing use
rates. Interestingly, risk perceptions rose in Colo-
rado in 2012–2013, immediately following legal-
ization. This rise may have resulted from public
safety and anti-legalization campaigns that cau-
tioned residents about the dangers of marijuana
use.
Data on marijuana prices may also shed light
on marijuana use. One hypothesis before legaliza-
tion was that use might soar because prices would
plunge. For example, Dale Gieringer, director of
California’s NORML (National Organization
for Reform of Marijuana Laws) branch, testified
in 2009 that in a “totally unregulated market, the
Figure 1Colorado National Survey on Use and Health Results (all respondents, aged 12+)
Source: National Survey on Drug Use and Health, Substance Abuse and Mental Health Services Administration (SAMHSA),
http://www.samhsa.gov/data/population-data-nsduh/reports?tab=33.
8
Figure 3Oregon National Survey on Drug Use and Health Results (all respondents, aged 12+)
Source: National Survey on Drug Use and Health, Substance Abuse and Mental Health Services Administration (SAMHSA), http://www.
samhsa.gov/data/population-data-nsduh/reports?tab=33.
Figure 2Washington State National Survey on Drug Use and Health Results (all respondents, aged 12+)
Source: National Survey on Drug Use and Health, Substance Abuse and Mental Health Services Administration (SAMHSA), http://www.
samhsa.gov/data/population-data-nsduh/reports?tab=33.
9
Figure 4Youth Risk Behavior Survey Past Month Marijuana Use
Source: Youth Risk Behavior Survey, Centers for Disease Control and Prevention, http://www.cdc.gov/healthyyouth/data/yrbs/data.htm.
Figure 5Perception of Risk
Source: National Survey on Drug Use and Health, Substance Abuse and Mental Health Services Administration (SAMHSA), http://www.samhsa.
gov/data/population-data-nsduh/reports?tab=33.
10
Figure 6Colorado Marijuana Prices
Source: Priceofweed.com, http://www.priceofweed.com/prices/United-States/Colorado.html.
Source: Priceofweed.com, http://www.priceofweed.com/prices/United-States/Washington.html.
Figure 7Washington Marijuana Prices
11“Overall, these data suggest no major drop in marijuana prices after legalization and conse-quently less likelihood of soaring use because of cheaper marijuana.”
price of marijuana would presumably drop as low
as that of other legal herbs such as tea or tobac-
co—on the order of a few dollars per ounce—100
times lower than the current prevailing price of
$300 per ounce.”43 A separate study by the Rand
Corporation44 estimated that marijuana prices in
California would fall by 80 percent after legaliza-
tion.45 Using data from Price of Weed (priceof-
weed.com), which crowdsources real-time infor-
mation from thousands of marijuana buyers in
each state, we derive monthly average prices
of marijuana in Colorado, Washington, and
Oregon.46 See Figures 6, 7, and 8.
In Colorado, monthly average prices were
declining even before legalization and have re-
mained fairly steady since. The cost of high-
quality marijuana hovers around $230 per ounce
while that of medium-quality marijuana remains
around $190. The opening of shops in January
2015 seems to have had little effect. In Washington
State, marijuana prices have been similarly steady
and have converged almost exactly to Colorado
prices—roughly $230 for high-quality marijuana
and $200 for medium-quality marijuana. Oregon
prices show a rise after legalization, catching up
to Colorado and Washington levels. Although we
cannot draw a conclusive picture on the basis of
consumer-reported data, the convergence of pric-
es across states makes sense. This convergence
is also consistent with the idea that legalization
helped divert marijuana commerce from the black
market to legalized retail shops.47 Overall, these
data suggest no major drop in marijuana prices af-
ter legalization and consequently less likelihood of
soaring use because of cheaper marijuana.
HEALTH AND SUICIDES
Previous studies have suggested a link be-
tween medicalization of marijuana and a lower
overall suicide rate, particularly among demo-
graphics most likely to use marijuana in general
(males ages 20 to 39).48 In fact, supporters believe
that marijuana can be an effective treatment for
Source: Priceofweed.com, http://www.priceofweed.com/prices/United-States/Oregon.html.
Figure 8Oregon Marijuana Prices
12
Figure 10Suicide Rates for Males 20–39 Years Old
Source: Centers for Disease Control and Prevention, CDC Wonder Portal, http://wonder.cdc.gov/.
Figure 9Annual Suicide Rates (per 100,000 people)
Source: Centers for Disease Control and Prevention, CDC Wonder Portal, http://wonder.cdc.gov/.
13“Suicide rates in all four states trend slightly upward, but it is difficult to see any associ-ation between marijuana legalization and any changes in these trends.”
bipolar disorder, depression, and other mood
disorders—not to mention a safer alternative to
alcohol. Moreover, the pain-relieving element of
medical marijuana may help patients avoid more
harmful prescription painkillers and tranquiliz-
ers.49 Conversely, certain studies suggest exces-
sive marijuana use may increase the risk of de-
pression, schizophrenia, unhealthy drug abuse,
and anxiety.50 Some research also warns about
long-lasting cognitive damage if marijuana is con-
sumed regularly, especially at a young age.51
Figure 9 displays the overall yearly suicide rate
per 100,000 people in each of the four legalizing
states between 1999 and 2014.52 Figure 10 pres-
ents the analogous suicide rate for males aged 20
through 39 years.53 Suicide rates in all four states
trend slightly upward during the 15-year-long pe-
riod, but it is difficult to see any association be-
tween marijuana legalization and any changes in
these trends. These findings contrast with many
previous studies, so it is possible that any effects
will take longer to appear. In addition, previous
research has suggested a link between medical
marijuana and a lower suicide rate; it is not obvi-
ous that recreational marijuana would lead to the
same result, or that legalization of recreational
marijuana after medical marijuana is already le-
galized would have much of an extra effect.54
Data on treatment center admissions provide
a proxy for drug abuse and other health hazards
associated with misuse. Figures 11 and 12 plot
rates of annual admissions involving marijuana
and alcohol to publicly funded treatment cen-
ters in Colorado55 and King County, Washington
(which encompasses Seattle).56 Marijuana admis-
sions in Colorado were fairly steady over the past
decade but began falling in 2013 and 2014, just
as legalization took effect. Alcohol admissions
began declining around the same time. In King
County, admissions for marijuana and alcohol
continued their downward trends after legaliza-
tion. These patterns suggest that extreme growth
in marijuana abuse has not materialized, as some
critics had warned before legalization.
Figure 11Colorado Treatment Admissions
Source: Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA) report, “The Legalization of Marijuana in Colorado: The Impact”
(Vol. 3, September 2015), http://www.rmhidta.org/html/2015%20final%20legalization%20of%20marijuana%20in%20colorado%20the%20impact.pdf.
14
CRIME
In addition to substance use and health
outcomes, legalization might affect crime. Op-
ponents think these substances cause crime
through psychopharmacological and other
mechanisms, and they note that such substances
have long been associated with crime, social de-
viancy, and other undesirable aspects of society.57
Although those perspectives first emerged in the
1920s and 1930s, marijuana’s perceived associa-
tions with crime and deviancy persist today.58
Before referendums in 2012, police chiefs,
governors, policymakers, and concerned citizens
spoke up against marijuana and its purported
links to crime.59 They also argued that expanding
drug commerce could increase marijuana com-
merce in violent underground markets and that
legalization would make it easy to smuggle the
substance across borders where it remained pro-
hibited, thus causing negative spillover effects.60
Proponents argue that legalization reduces
crime by diverting marijuana production and
sale from the black market to legal venues. This
shift may be incomplete if high tax rates or sig-
nificant regulation keeps some marijuana ac-
tivity in gray or black markets, but this merely
underscores that more legalization means less
crime. At the same time, legalization may re-
duce the burden on law enforcement to patrol
for drug offenses, thereby freeing budgets and
manpower to address larger crimes. Legaliza-
tion supporters also dispute the claim that
marijuana increases neurological tendencies
toward violence or aggression.61
Figure 13 presents monthly crime rates from
Denver, Colorado, for all reported violent crimes
and property crimes.62 Both metrics remain es-
sentially constant after 2012 and 2014; we do not
observe substantial deviations from the illustrat-
ed cyclical crime pattern. Other cities in Colo-
rado mirror those findings. Analogous monthly
crime data for Fort Collins, for example, reveal
no increase in violent or property crime.63
Figure 14 shows monthly violent and prop-
erty crime rates as reported by the Seattle Po-
lice Department.64 Both categories of crime
Figure 12Treatment Admissions by Drug—King County, Washington
Source: University of Washington Alcohol and Drug Abuse Institute, http://adai.washington.edu/pubs/cewg/Drug%20Trends_2014_final.pdf.
15
Figure 13Denver Monthly Crime Rate (violent and property crime rates per 100,000 residents)
Source: Denver Police Department, Monthly Crime Reports, https://www.denvergov.org/content/denvergov/en/police-department/
crime-information/crime-statistics-maps.html. Population data source: U.S. Census Bureau Estimates, http://www.census.gov/popest/
data/intercensal/index.html.
Source: Seattle Police Department, Online Crime Dashboard, http://www.seattle.gov/seattle-police-department/crime-data/crime-
dashboard. Population data source: U.S. Census Bureau Estimates. http://www.census.gov/popest/data/intercensal/index.html.
Figure 14Seattle Monthly Crime Rate
16“All told, crime in Seattle has neither soared nor plummeted in the wake of legaliza-tion.”
declined steadily over the past 20 years, with no
major deviations after marijuana liberalization.
Property crime does appear to spike in 2013
and early 2014, and some commentators have
posited that legalization drove this increase.65
That connection is not convincing, however,
since property crime starts to fall again after
the opening of marijuana shops in mid-2014.
All told, crime in Seattle has neither soared nor
plummeted in the wake of legalization.66
Monthly violent and property crime re-
mained steady after legalization in Portland, Or-
egon, as seen in Figure 15.67 Portland provides an
interesting case because of its border with Wash-
ington. Between 2012 and 2014, Portland (and the
rest of Oregon) prohibited the recreational use of
marijuana, while marijuana sales and consump-
tion were fully legal in neighboring Washingto-
nian towns just to the north. This situation cre-
ates a natural experiment that allows us to look
for spillover effects in Oregon. Figure 15 suggests
that legalization in Washington and the opening
of stores there did not produce rising crime rates
across the border. Elsewhere in Oregon, we see
no discernible changes in crime trends before
and after legalization or medical marijuana liber-
alization.68
ROAD SAFETY
We next evaluate how the incidence of traf-
fic accidents may have changed in response to
marijuana policy changes. Previous literature
and political rhetoric suggest two contrasting hy-
potheses. One holds that legalization increases
traffic accidents by spurring drug use and there-
by driving under the influence. This hypothesis
presumes that marijuana impairs driving abil-
ity.69 The opposing theory argues legalization
improves traffic safety because marijuana substi-
tutes for alcohol, which some studies say impairs
driving ability even more.70 Moreover, some con-
sumers may be able to drive better if marijuana
serves to relieve their pain.
Figure 15Portland Monthly Crime Rate
Source: Portland Police Bureau Neighborhood Statistics, http://www.portlandonline.com/police/crimestats/. Population data source: U.S. Census
Bureau Estimates, http://www.census.gov/popest/data/intercensal/index.html.
17
Figure 16Colorado Car Crashes and Fatality Rate
Source: Colorado Department of Transportation, http://www.coloradodot.info/library/traffic/traffic-manuals-guidelines/safety-crash-data/
fatal-crash-data-city-county/fatal-crashes-by-city-and-county/.
Figure 17Washington Car Crashes and Fatality Rate
Source: Washington Traffic Safety Commission, Quarterly Target Zero Reports, http://wtsc.wa.gov/research-data/quarterly-target-zero-
data/.
18
Rhetoric from experts and government of-
ficials has been equally divided. Kevin Sabet, a
former senior White House drug policy adviser,
warned that potential consequences of Colora-
do’s legalization could include large increases in
traffic accidents.71 A recent Associated Press ar-
ticle noted that “fatal crashes involving marijuana
doubled in Washington after legalization.”72 Yet
Coloradan law enforcement agents are them-
selves unsure whether legal marijuana has led to
an increase in accidents.73 Research by Radley
Balko, an opinion blogger for the Washington
Post and an author on drug policy, claims that,
overall, “highway fatalities in Colorado are at
near-historic lows” in the wake of legalization.74
Figure 16 presents the monthly rate of fatal
accidents and fatalities per 100,000 residents
in Colorado.75 No spike in fatal traffic acci-
dents or fatalities followed the liberalization
of medical marijuana in 2009.76 Although fa-
tality rates have reached slightly higher peaks
in recent summers, no obvious jump occurs
after either legalization in 2012 or the open-
ing of stores in 2014.77 Likewise, neither mari-
juana milestone in Washington State appears
to have substantially affected the fatal crash
or fatality rate, as illustrated in Figure 17.78 In
fact, more granular statistics reveal that the
fatality rate for drug-related crashes was virtu-
ally unchanged after legalization.79
Figure 18 depicts the crash fatality rate in
Oregon.80 Although few post-legalization data
were available at the time of publication, we
observe no signs of deviations in trend after the
opening of medical marijuana dispensaries in
2013. We can also test for possible spillover ef-
fects from neighboring Washington. Legaliza-
tion there in 2012 and the opening of marijuana
shops in 2014 do not seem to materially affect
road fatalities in Oregon in either direction.
Finally, Figure 19 presents annual data on
crash fatality rates in Alaska; these show no
discernible increase after legalization and may
even decline slightly.
Figure 18Oregon Car Crash Fatality Rate
Source: Oregon Department of Transportation, online Crash Summary Reports and in-person data request. Special thanks to Theresa
Heyn and Coleen O’Hogan, http://www.oregon.gov/ODOT/TD/TDATA/pages/car/car_publications.aspx.
19
YOUTH OUTCOMES
Much of the concern surrounding marijuana
legalization relates to its possible effect on youths.
Many observers, for example, fear that expanded
legal access—even if officially limited to adults
age 21 and over—might increase use by teenagers,
with negative effects on intelligence, educational
outcomes, or other youth behaviors.81, 82
Figure 20 displays the total number of school
suspensions and drug-related suspensions in Col-
orado public high schools during each academic
year.83 Total suspensions trend downward over
time, with a slight bump after 2014, but that bump
was not one driven by drug-related causes. Drug-
related suspensions appear to rise after medical
marijuana commercialization in 2009 but stay
level after full legalization and the opening of re-
tail shops. Figure 21 shows public high school ex-
pulsions, both overall and drug-related. It reveals
a parallel bump in drug-related expulsions right
after marijuana liberalization in 2009, but expul-
sions drop steeply thereafter. In fact, by 2014, ex-
pulsions drop back to their previous levels.
We also consider potential effects on aca-
demic performance. Standardized test scores
measuring the reading proficiency of 8th and
10th graders in Washington State show no
indication of significant positive or negative
changes caused by legalization, as illustrated in
Figure 22.84 Although some studies have found
that frequent marijuana use impedes teen cog-
nitive development, our results do not suggest a
major change in use, thereby implying no major
changes in testing performance.
ECONOMIC OUTCOMES
Changing economic and demographic out-
comes are unlikely to be significant effects of
marijuana legalization, simply because marijua-
na is a small part of the overall economy. Nev-
ertheless, we consider this outcome for com-
pleteness. Before legalization, many advocates
thought that legalization could drive a robust
influx of residents, particularly young individu-
als enticed to move across state lines to take ad-
Figure 19Alaska Car Crashes and Fatalities
Source: Alaska Highway Safety Office, http://www.dot.state.ak.us/stwdplng/hwysafety/fars.shtml.
20
Figure 20School Suspensions—Colorado
Source: Colorado Department of Education, 10-Year Trend Data, http://www.cde.state.co.us/cdereval/suspend-expelcurrent.
Figure 21School Expulsions—Colorado
Source: Colorado Department of Education, http://www.cde.state.co.us/cdereval/suspend-expelcurrent.
21
vantage of loose marijuana laws. More recently,
various news articles say housing prices in Col-
orado (particularly around Denver) are soaring
at growth rates far above the national average,
perhaps as a consequence of marijuana legaliza-
tion. One analyst went so far as to say that mari-
juana has essentially “kick-started the recovery
of the industrial market in Denver” and led to
record-high rent levels.85
Figure 23 sheds doubt on these extreme claims
by presenting the Case-Shiller Home Price Index
for Denver, Seattle, and Portland, along with the
national average.86 Data show that home prices
in all three cities have been rising steadily since
mid-2011, with no apparent booms after mari-
juana policy changes. Housing prices in Denver
did rise at a robust rate after January 2014, when
marijuana shops opened, but this increase was in
step with the national average.
Furthermore, marijuana legalization in all
four legalizing states had, at most, a trivial ef-
fect on population growth.87 Whereas some
people may have moved across states for mari-
juana purposes, any resulting growth in popu-
lation has been small and unlikely to cause
noticeable increases in housing prices or total
economic output.
Advocates also argue that legalization boosts
economic activity by creating jobs in the mari-
juana sector, including “marijuana tourism”
and other support industries, thereby boost-
ing economic output.88 Marijuana production
and commerce do employ many thousands of
people, and Colorado data provide some hint
of a measurable effect on employment. As Fig-
ure 24 indicates, the seasonally adjusted unem-
ployment rate began to fall more dramatically
after the start of 2014, which coincides with
the opening of marijuana stores.89 These gains,
however, have yet to be seen in Washington, Or-
egon, and Alaska. One hypothesis may be that
Colorado, as the first state to open retail shops,
benefitted from a “first mover advantage.” If
more states legalize, any employment gains will
become spread out more broadly, and marijuana
tourism may diminish.
Figure 22Washington Standardized Test Scores
Source: Washington State Office of the Superintendent of Public Instruction, http://reportcard.ospi.k12.wa.us/.
22
Figure 23Case Shiller Home Price Index
Source: S&P Core Logic Case-Shiller Home Price Indices, http://us.spindices.com/index-family/real-estate/sp-corelogic-case-shiller.
Figure 24Unemployment Rates
Source: Bureau of Labor Statistics, Local Area Unemployment Statistics, http://www.bls.gov/lau/.
Note: Rates are seasonally adjusted.
23
Figure 25Marijuana Tax Revenues—Colorado (all values are nominal)
Source: Colorado Department of Revenue, https://www.colorado.gov/pacific/revenue/colorado-marijuana-tax-data.
Figure 26Marijuana Tax Revenues—Washington (all values are nominal)
Source: Washington State Department of Revenue, http://dor.wa.gov/Content/AboutUs/StatisticsAndReports/stats_MMJTaxes.aspx; Initiative
502 Data, http://www.502data.com/.
24
Figure 27State Correctional Expenditures (all values are nominal)
Source: United States Census Bureau, American FactFinder Database, http://factfinder.census.gov/.
Figure 28State Police Protection Expenditures (all values are nominal)
Source: United States Census Bureau, American FactFinder Database, http://factfinder.census.gov/.
25“One area where legal marijuana has reaped unexpectedly large benefits is state tax revenue.”
Data from the Bureau of Economic Analysis
show little evidence of significant gross domes-
tic product (GDP) increases after legalization
in any state.90 Although it is hard to disentan-
gle marijuana-related economic activity from
broader economic trends, the surges in eco-
nomic output predicted by some proponents
have not yet materialized. Similarly, no clear
changes have occurred in GDP per capita.
One area where legal marijuana has reaped
unexpectedly large benefits is state tax revenue.
Colorado, Washington, and Oregon all impose
significant excise taxes on recreational marijuana,
along with standard state sales taxes, other local
taxes, and licensing fees. As seen in Figure 25, Col-
orado collects well over $10 million per month
from recreational marijuana alone.91 In 2015 the
state generated a total of $135 million in recre-
ational marijuana revenue, $35 million of which
was earmarked for school construction projects.
These figures are above some pre-legalization
forecasts, although revenue growth was disap-
pointingly sluggish during the first few months of
sales.92 A similar story has unfolded in Washing-
ton, as illustrated in Figure 26, where recreational
marijuana generated approximately $70 million
in tax revenue in the first year of sales93—double
the original revenue forecast.94 Oregon only
began taxing recreational marijuana in January
2016, so data are still preliminary; however, state
officials report revenues of $14.9 million so far,
well above the initial estimate of $2.0 million to
$3.0 million for the entire calendar year.95 The
tax revenues in these states may decline.
Limited post-legalization data prevent us
from ruling out small changes in marijuana use
or other outcomes. As additional post-legal-
ization data become available, expanding this
analysis will continue to inform the debate.
The data so far provide little support for the
strong claims about legalization made by ei-
ther opponents or supporters.
NOTES
1. In November 2014, the District of Columbia
voted overwhelmingly in favor of Initiative 71,
which legalized the use, possession, and cultiva-
tion of limited amounts of marijuana in the pri-
vacy of one’s home. It also permitted adults age 21
and over to “gift”—or transfer—up to two ounces
of marijuana provided no payment or other ex-
change of goods or services occurred. Selling mar-
ijuana or consuming it in public, however, remain
criminal violations. In addition, because of ongo-
ing federal prohibition, marijuana remains illegal
on federal land, which makes up 30 percent of the
District. Therefore, we do not examine data for
D.C. For more, see http://mpdc.dc.gov/marijuana.
2. In June 2016, the California secretary of state an-
nounced that a ballot referendum on marijuana legal-
ization would occur in November, after a state cam-
paign amassed enough signatures to put the question
to a vote. Other likely candidates include Arizona,
Florida, Maine, Massachusetts, Michigan, Missouri,
Nevada, New York, Rhode Island, and Vermont. Or-
ganizations and private citizens in additional states
have raised the idea of ballot initiatives but have not
yet garnered the requisite signatures to hold a vote.
See Jackie Salo, “Marijuana Legalization 2016: Which
States Will Consider Cannabis This Year,” Interna-
tional Business Times, December 30, 2015, http://www.
ibtimes.com/marijuana-legalization-2016-which-
states-will-consider-cannabis-year-2245024.
3. Ethan Nadelmann, for example, has asserted
that legalization is a “smart” move that will help end
mass incarceration and undermine illicit criminal
organizations. See Nadelmann, “Marijuana Legal-
ization: Not If, But When,” HuffingtonPost.com,
November 3, 2010, http://www.huffingtonpost.
com/ethannadelmann/marijuana-legalization-
no_b_778222.html.
Former New Mexico governor and current Lib-
ertarian Party presidential candidate Gary Johnson
has also advocated marijuana legalization, predicting
that the measure will lead to less overall substance
abuse because individuals addicted to alcohol or other
substances will find marijuana a safer alternative. See
Kelsey Osterman, “Gary Johnson: Legalizing Mari-
juana Will Lead to Lower Overall Substance Abuse,”
RedAlertPolitics.com, April 24, 2013, http://redalertpo
litics.com/2013/04/24/gary-johnson-legalizing-mar
ijuana-will-lead-to-less-overall-substance-abuse/.
26
Denver Police Chief Robert White argues that
violent crime dropped almost 9 percent in 2012.
See Sadie Gurman, “Denver’s Top Law Enforce-
ment Officials Disagree: Is Crime Up or Down?”
Denver Post, January 22, 2014, http://www.denver
post.com/2014/01/22/denvers-top-law-enforce
ment-officers-disagree-is-crime-up-or-down/.
4. Colorado governor John Hickenlooper (D)
opposed initial efforts to legalize marijuana be-
cause he thought the policy would, among other
things, increase the number of children using drugs.
See Matt Ferner, “Gov. John Hickenlooper Oppos-
es Legal Weed,” HuffingtonPost.com, September 12,
2012, http://www.huffington post.com/2012/09/12/
gov-john-hickenlooper-opp_n_1879248.html.
Former U.S. attorney general Edwin Meese
III, who is now the Heritage Foundation’s Ron-
ald Reagan Distinguished Fellow Emeritus, and
Charles Stimson have argued that violent crime
surges when marijuana is legally abundant and
that the economic burden of legalization far out-
strips the gain. See Meese and Stimson, “The Case
against Legalizing Marijuana in California,” Heri-
tage Foundation, October 3, 2010, http://www.
heritage.org/research/commentary/2010/10/the-
case-against-legalizing-marijuana-in-california.
Kevin Sabet, a former senior White House
drug policy adviser in the Obama administration,
has called Colorado’s marijuana legalization a mis-
take, warning that potential consequences may
include high addiction rates, spikes in traffic acci-
dents, and reductions in IQ. See Sabet, “Colorado
Will Show Why Legalizing Marijuana Is a Mis-
take,” Washington Times, January 17, 2014, http://
www.washingtontimes.com/news/2014/jan/17/
sabet-marijuana-legalizations-worst-enemy/.
The former director of the Drug Enforcement
Administration, John Walters, claims that “what
we [see] in Colorado has the markings of a drug
use epidemic.” He argues that there is now a thriv-
ing black market in marijuana in Colorado and
that more research on marijuana’s societal effects
needs to be completed before legalization should
be considered. See Walters, “The Devastation
That’s Really Happening in Colorado,” Weekly
Standard, July 10, 2014, http://www.weeklystandard
.com/the-devastation-thats-really-happening-in-
colorado/article/796308.
John Walsh, the U.S. attorney for Colorado, de-
fended the targeted prosecution of medical mari-
juana dispensaries located near schools by citing
figures from the Colorado Department of Educa-
tion showing dramatic increases in drug-related
school suspensions, expulsions, and law enforce-
ment referrals between 2008 and 2011. See John
Ingold, “U.S. Attorney John Walsh Justifies Fed-
eral Crackdown on Medical-Marijuana Shops,”
Denver Post, January 20, 2012, http://www.denver
post.com/2012/01/19/u-s-attorney-john-walsh-
justifies-federal-crackdown-on-medical-marijuana-
shops-2/.
Denver District Attorney Mitch Morrissey
points to the 9 percent rise in felony cases submit-
ted to his office during the 2008–11 period, after
Colorado’s marijuana laws had been partially lib-
eralized, as evidence of marijuana’s social effects.
See Sadie Gurman, “Denver’s Top Law Enforce-
ment Officials Disagree: Is Crime Up or Down?”
Denver Post, January 22, 2014, http://www.denver-
post.com/2014/01/22/denvers-top-law-enforce-
ment-officers-disagree-is-crime-up-or-down/.
Other recent news stories that report criticisms
of marijuana liberalization include Jack Healy,
“After 5 Months of Legal Sale, Colorado Sees the
Downside of a Legal High,” New York Times, May
31, 2014, http://www.nytimes.com/2014/06/01/us/
after-5-months-of-sales-colorado-sees-the-down-
side-of-a-legal-high.html, and Josh Voorhees, “Go-
ing to Pot, Slate.com, May 21, 2014, http://www.slate.
com/articles/news_and_politics/politics/2014/05/
colorado_s_pot_experiment_the_unintended_
consequences_of_marijuana_legalization.html.
Also, White House policy research indicates
that marijuana is the drug most often linked to
crime. See Rob Hotakainen, “Marijuana Is Drug
Most Often Linked to Crime,” McClatchy News
Service, May 23, 2013, http://www.mcclatchydc.
com/news/politics-government/article24749413.
html.
5. MacCoun et al. (2009) review the decriminaliza-
tion literature from the first wave of decriminaliza-
tions in the 1970s, noting a lack of response. See
MacCoun et al.,“Do Citizens Know Whether Their
State Has Decriminalized Marijuana? Assessing the
27
Perceptual Component of Deterrence Theory.” Re-
view of Law and Economics 5 (2009): 347–71. Analysis
of the recent U.S. state legalizations is more limited.
Some noteworthy studies include Jeffrey
Miron, “Marijuana Policy in Colorado,” Cato Insti-
tute Working Paper no. 24, 2014; Andrew A. Monte
et al., “The Implications of Marijuana Legalization
in Colorado,” Journal of the American Medical Asso-
ciation 313, no. 3 (2015): 241–42; Stacy Salomonsen-
Sautel et al., “Trends in Fatal Motor Vehicle Crash-
es Before and After Marijuana Commercializa-
tion in Colorado,” Drug and Alcohol Dependence
140 (2014): 137–44, which found a statistically sig-
nificant uptick in drivers involved in a fatal motor
vehicle crash after commercialization of medical
marijuana in Colorado; Beau Kilmer et al., “Altered
State?: Assessing How Marijuana Legalization in
California Could Influence Marijuana Consump-
tion and Public Budgets,” Occasional Paper, Rand
Drug Policy Research Center, Santa Monica, CA,
2010; Angela Hawken et al., “Quasi-Legal Cannabis
in Colorado and Washington: Local and National
Implications,” Addiction 108, no. 5 (2013): 837–38;
and Howard S. Kim et al., “Marijuana Tourism and
Emergency Department Visits in Colorado,” New
England Journal of Medicine, 374 (2016): 797–98.
For an analysis of whether Colorado has im-
plemented its legalization in a manner consistent
with the law, see John Hudak, “Colorado’s Rollout
of Legal Marijuana Is Succeeding,” Governance
Studies Series, Brookings Institution, Washing-
ton, D.C., July 31, 2014, http://www.brookings.
edu/~/media/research/files/papers/2014/07/colo
rado-marijuana-legalization-succeeding/cepm
mjcov2.pdf. International evidence from Portu-
gal (Glenn Greenwald, “Drug Decriminalization
in Portugal,” Cato Institute White Paper, 2009,
http://object.cato.org/sites/cato.org/files/pubs/
pdf/greenwald_whitepaper.pdf), the Netherlands
(Robert J. MacCoun, “What can we learn from
the Dutch cannabis coffeeshop system,” Addic-
tion 2011: 1-12 and Ali Palali and Jan C. van Ours,
“Distance to Cannabis Shops and Age of Onset
of Cannabis Use,” Health Economics 24, 11 (2015):
1482-1501, parts of Australia (Jenny Williams and
Anne Line Bretteville-Jensen, “Does Liberalizing
Cannabis Laws Increase Cannabis Use?” Journal
of Health Economics 36 (2014): 20-32) and parts of
London (Nils Braakman and Simon Jones, “Can-
nabis Depenalization, Drug Consumption and
Crime–Evidence from the 2004 Cannabis Declas-
sification in the UK,” Social Science and Medicine
115(2014): 29-37) suggest little to no effects of
these laws on drug use. Jérôme Adda et al., “Crime
and the Depenalization of Cannabis Possession:
Evidence from a Policing Experiment,” Journal of
Political Economy, 122, no. 5 (2014): 1130-1201 con-
sider depenalization in a London borough, find-
ing declines in crime caused by the police shifting
enforcement to non-drug crime.
6. Opium, cocaine, coca leaves, and other deriva-
tives of coca and opium had been essentially out-
lawed in 1914 by the Harrison Narcotic Act. See
C. E. Terry, “The Harrison Anti-Narcotic Act,”
American Journal of Public Health 5, no. 6 (1915): 518,
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC
1286619/?page=1.
7. “When and Why Was Marijuana Outlawed,”
Schaffer Library of Drug Policy, http://druglibrary.
org/schaffer/library/mj_outlawed.htm.
8. Ibid.
9. Mathieu Deflem, ed., Popular Culture, Crime, and
Social Control, vol. 14, Sociology of Crime, Law and
Deviance (Bingley, UK: Emerald Group Publishing,
2010), p. 13, https://goo.gl/ioAoVY.
10. Kathleen Ferraiolo, “From Killer Weed to
Popular Medicine: The Evolution of Drug Control
Policy, 1937–2000,” The Journal of Policy History 19
(2007): 147–79, https://muse.jhu.edu/article/ 217587.
11. David Musto, “Opium, Cocaine and Marijuana
in American History,” Scientific American 20-27 (July
1991), http://www.ncbi.nlm.nih.gov/pubmed/1882226.
12. United Nations Office on Drugs and Crime,
“Traffic in Narcotics, Barbiturates and Amphet-
amines in the United States,” https://www.unodc.
org/unodc/en/data-and-analysis/bulletin/bulle-
tin_1956-01-01_3_page005.html.
13. “Drug Schedules,” U.S. Drug Enforcement
28
Administration, https://www.dea.gov/druginfo/
ds.shtml.
14. The 11 states were Oregon (1973), Alaska (1975),
California (1975), Colorado (1975), Maine (1975),
Minnesota (1976), Ohio (1976), Mississippi (1977),
New York (1977), North Carolina (1977), and Ne-
vada (1978). See Rosalie Pacula et al., “Marijuana
Decriminalization: What Does It Mean for the
United States?” (National Bureau of Economic
Research Working Paper no. 9690, NBER and
RAND Corporation, Cambridge, MA, January
2004), http://www.rand.org/content/dam/rand/
pubs/working_papers/2004/RAND_WR126.pdf.
15. Not all states followed such a straightforward
path towards marijuana liberalization. Alaska, for
example, decriminalized marijuana use and posses-
sion in one’s home in 1975. In 1990, however, a voter
initiative recriminalized possession and use of mari-
juana. See the section on Alaska for more details.
16. “States That Have Decriminalized,” National
Organization for the Reform of Marijuana Laws,
http://norml.org/aboutmarijuana/item/states-
that-have-decriminalized.
17. “The Legalization of Marijuana in Colorado:
The Impact. A Preliminary Report,” Rocky Moun-
tain HIDTA 1 (August 2013): 3, http://www.rm
hidta.org/html/final%20legalization%20of%20
mj%20in%20colorado%20the%20impact.pdf.
18. David Ogden, the deputy attorney general at
the time, issued a memorandum stating it would
be unwise to “focus federal resources . . . on indi-
viduals whose actions are in clear and unambiguous
compliance with existing state law providing for the
medical use of marijuana.” See “Memorandum for
Selected United State Attorneys on Investigations
and Prosecutions in States Authorizing the Medical
Use of Marijuana,” U.S. Department of Justice, Oc-
tober 19, 2009. https://www.justice.gov/opa/blog/
memorandum-selected-united-state-attorneys-
investigations-and-prosecutions-states.
19. The Ogden Memorandum did not perma-
nently resolve confusion about the role of federal
law in state marijuana policy. In 2011, the Depart-
ment of Justice issued another memo entitled
the “Cole Memo” which somewhat backpedaled
on the Ogden Memo’s position; it cautioned that
“the Ogden Memorandum was never intended to
shield such activities from federal enforcement ac-
tion and prosecution, even where those activities
purport to comply with state law.” It was not until
2013 when those in the marijuana industry received
a clear answer. A third memo unambiguously out-
lined the eight scenarios in which federal authori-
ties would enforce marijuana laws in states where
the substance was legal. Beyond those eight priori-
ties, the federal government would leave marijuana
law enforcement to local authorities. For more, see
“Guidance Regarding the Ogden Memo in Juris-
dictions Seeking to Authorize Marijuana for Medi-
cal Use,” U.S. Department of Justice, June 29, 2011,
https://www.justice.gov/sites/default/files/oip/
legacy/2014/07/23/dag-guidance-2011-for-medical-
marijuana-use.pdf. See also “Guidance Regarding
Marijuana Enforcement,” U.S. Department of Jus-
tice, August 29, 2013, https://www.justice.gov/iso/
opa/resources/30520 13829132756857467.pdf.
20. “The Legalization of Marijuana in Colorado:
The Impact. A Preliminary Report,” Rocky Moun-
tain HIDTA 1 (August 2013): 4, http://www.rm
hidta.org/html/final%20legalization%20of%20
mj%20in%20colorado%20the%20impact.pdf.
21. “Amendment 64: Use and Regulation of Mari-
juana,” City of Fort Collins, Colorado, http://
www.fcgov.com/mmj/pdf/amendment64.pdf.
22. Ibid.
23. Numerous counties, including Denver County
and others, have enacted local taxes on top of state
taxes. In Denver, retail marijuana products are
subject to a local sales tax of 3.65 percent in addi-
tion to a special marijuana tax of 3.5 percent. See
“City and County of Denver, Colorado: Tax Guide,
Topic No. 95,” City of Denver (revised April 2015),
https://www.denvergov.org/Portals/571/documents/
TaxGuide/Marijuana-Medical_and_Retail.pdf.
24. This system of three separate taxes was eventu-
29
ally replaced by a single, 37 percent excise tax levied
at the retail point of sale in July 2015. See “FAQs on
Taxes,” Washington State Liquor and Cannabis
Board, http://www.liq.wa.gov/mj2015/faqs-on-
taxes. See also Rachel La Corte, “Washington State
Pot Law Overhaul: Marijuana Tax Reset at 37 Per-
cent,” Associated Press, The Cannabist, July 1, 2015,
http://www.thecannabist.co/2015/07/01/washing-
ton-state-pot-law-overhaul-marijuana-tax-reset-at-
37-percent/37238/.
25. “State by State Laws: Oregon,” National Orga-
nization for the Reform of Marijuana Laws, 2006,
http://norml.org/laws/item/oregon-penalties-2.
26. See “Oregon Legislature Ends 24 Years of Mari-
juana Decriminalization,” National Organization
for the Reform of Marijuana Laws, news release,
July 3, 1997, http://norml.org/news/1997/07/03/
oregon-legislature-ends-24-years-of-marijuana-
decrimnalization/. See also “State by State Laws:
Oregon,” National Organization for the Reform of
Marijuana Laws, 2006.
27. “Medical Marijuana Rules and Statutes: Or-
egon Medical Marijuana Act,” Oregon Health
Authority, June 2016, http://public.health.oregon.
gov/DiseasesConditions/ChronicDisease/Medical
MarijuanaProgram/Pages/legal.aspx#ors.
28. “Oregon Medical Marijuana Allowance Mea-
sure 33 (2004),” Ballotpedia, https://ballotpedia.
org/Oregon_Medical_Marijuana_Allowance_
Measure_33_(2004).
29. “Oregon Medical Marijuana Program Statis-
tics,” Oregon Health Authority, July 2016, https://
public.health.oregon.gov/diseasesconditions/
chronicdisease/medicalmarijuanaprogram/pages/
data.aspx.
30. “Oregon Marijuana Legalization for Personal
Use, Ballot Measure 5 (1986),” Ballotpedia, https://
ballotpedia.org/Oregon_Marijuana_Legalization_
for_Personal_Use,_Ballot_Measure_5_(1986).
31. “Oregon Cannabis Tax Act Initiative, Measure 80
(2012),” Ballotpedia, https://ballotpedia.org/Oregon_
Cannabis_Tax_Act_Initiative,_Measure_80_(2012).
32. “Measure 91,” Oregon Liquor Control Com-
mission, https://www.oregon.gov/olcc/marijuana/
Documents/Measure91.pdf.
33. Several counties in Oregon have enacted their
own local taxes.
34. As of June 2016, 87 municipalities and 19 coun-
ties in Oregon had prohibited recreational marijua-
na businesses or producers in their jurisdiction. See
“Record of Cities/Counties Prohibiting Licensed
Recreational Marijuana Facilities,” Oregon Liquor
Control Commission, https://www.oregon.gov/
olcc/marijuana/Documents/Cities_Counties_RMJ
OptOut.pdf.
35. “Medical Marijuana Dispensary Directory,”
Oregon Health Authority http://www.oregon.gov/
oha/mmj/Pages/directory.aspx.
36. Ravin v. State, 537 F.2d 494 (Alaska 1975).
37. “Alaska Marijuana Criminalization Initiative,
Measure 2 (1990),” Ballotpedia, https://ballotpedia.
org/Alaska_Marijuana_Criminalization_Initiative_
Measure_2_(1990).
38. “Ballot Measure 8: Bill Allowing Medical Use
of Marijuana,” Alaska Division of Elections, http://
www.elections.alaska.gov/doc/oep/1998/98bal8.
htm.
39. Recent work includes the following: D. Mark
Anderson et al., “Medical Marijuana Laws and
Suicides by Gender and Age,” American Journal of
Public Health 104, no. 1 (December 2014): 2369–76;
D. Mark Anderson et al., “Medical Marijuana Laws
and Teen Marijuana Use,” American Law and Eco -
nomic Review 17, no. 2 (2015): 495–528; Choo, Esther
K et al., “The Impact of State Medical Marijuana
Legislation on Adolescent Marijuana Use,” Journal
of Adolescent Health, forthcoming.
Yu-Wei Luke Chu, “Do Medical Marijuana Laws
Increase Hard-Drug Use?” Journal of Law and Eco-
nomics 58, no. 2 (May 2015): 481–517; Gorman, Dennis
M. and J. Charles Huber, Jr. “Do Medical Cannabis
30
Laws Encourage Cannabis Use?” The International
Journal of Drug Policy, 18, no. 3 (Ma7 2007): 160–67;
S. Harper et al., “Do Medical Marijuana Laws In-
crease Marijuana Use? Replication Study and Ex-
tension,” Annals of Epidemiology 22(2012): 207-212;
Sarah D. Lynne-Landsman et al., “Effects of State
Medical Marijuana Laws on Adolescent Marijuana
Use,” American Journal of Public Health, 103(2013):
1500-1506; Karen O’Keefe and Mitch Earleywine,
“Marijuana Use by Young People: The Impact of
State Medical Marijuana Laws,” manuscript, Mari-
juana Policy Project (2011) and Hefei Wen et al.,
“The Effect of Medical Marijuana Laws on Mari-
juana, Alcohol, and Hard Drug Use,” NBER Work-
ing Paper no. 20085, National Bureau of Economic
Research, Cambridge, MA, 2014, which found that
medical marijuana laws led to a relatively small in-
crease in marijuana use by adults over age 21 and did
nothing to change use of hard drugs.
Rosalie Liccardo Pacula et al., “Assessing the
Effects of Medical Marijuana Laws on Marijuana
and Alcohol Use: The Devil Is in the Details,”
NBER Working Paper no. 19302, National Bu-
reau of Economic Research, Cambridge, MA,
2015, found that legalizing home cultivation and
medical marijuana dispensaries were associated
with higher marijuana use, while other aspects of
medical marijuana liberalization were not.
Choo et al., “The Impact of State Medical Mari-
juana Legislation on Adolescent Marijuana Use,”
Journal of Adolescent Health 55, no. 2 (2014): 160–66,
found no statistically significant differences in
adolescent marijuana use after state-level medical
marijuana legalization.
40. Data are reported as two-year averages. Data
are from “National Survey on Drug Use and Health
2002–2014,” Center for Behavioral Health Sta-
tistics and Quality, Substance Abuse and Mental
Health Services Administration, http://www.icpsr.
umich.edu/icpsrweb/content/SAMHDA/help/
nsduh-estimates.html.
41. No post-legalization data were available for
Alaska.
42. State-level data from “National Survey on
Drug Use and Health, 2002–2014,” Center for
Behavioral Health Statistics and Quality.
43. Dale H. Gieringer, director, California
NORML, “Testimony on the Legalization of
Marijuana,” Testimony before the California As-
sembly Committee on Public Safety, October 28,
2009, http://norml.org/pdf_files/AssPubSafety_
Legalization.pdf.
44. Rand Corporation, “Legalizing Marijuana in
California Would Sharply Lower the Price of the
Drug,” news release, July 7, 2007, http://www.rand.
org/news/press/2010/07/07.html.
45. These analyses consider legalization at both
the federal and state levels which would allow ad-
ditional avenues for lower prices such as economies
of scale, although also additional avenues for higher
prices because of federal taxation and advertising.
46. The website Price of Weed allows anyone to
submit anonymous data about the price, quantity,
and quality of marijuana he or she purchases, as well
as where the marijuana was purchased. Founded in
2010, the website has logged hundreds of thousands
of entries across the country, and many analysts and
journalists look to it as a source of marijuana price
data. It has obvious limitations: the data are not a
random sample; the consumer reports do not dis-
tinguish between marijuana bought through legal
means and through the black market; self-reported
data may not be accurate; and the data are probably
from a self-selecting crowd of marijuana enthusi-
asts. Nevertheless, Price of Weed provides large
samples of real-time data. To reduce the impact of
inaccurate submissions, the website automatically
removes the bottom and top 5 percent of outliers
when calculating its average prices. We were not
able to calculate meaningful marijuana price aver-
ages from Alaska because of a relatively low num-
ber of entries from that state.
47. One further trend we observe in all three
states is a widening price gap between high-qual-
ity and medium-quality marijuana. Among other
things, this gap may be the result of fewer infor-
mation asymmetries in the marijuana market. On
the black market, it can be hard to know the true
31
quality of a product. Marijuana trade is complex,
with hundreds of different strains and varieties.
Yet in the black market, consumers often have a
difficult time differentiating between them and
may end up paying similarly high prices for medi-
um- and high-quality marijuana. In all three states,
the gap between the prices rose after legalization,
suggesting that consumers have had an easier
time distinguishing between different qualities
and strains of marijuana.
48. Anderson, Rees, and Sabia, “Medical Marijua-
na Laws and Suicides by Gender and Age.”
49. D. Mark Anderson et al., “High on Life?: Medi-
cal Marijuana and Suicide,” Cato Institute Research
Briefs in Economic Policy, no. 17, January 2015,
http://www.southerncannabis.org/wp-content/up
loads/2015/01/marijuana-suicide-study.pdf.
David Powell et al., “Do Medical Marijuana
Laws Reduce Addictions and Deaths Related to
Pain Killers?” NBER Working Paper no. 21345,
National Bureau of Economic Research, Cam-
bridge, MA, July 2015.
50. See, for example, Zammit et al., “Self-reported
Cannabis Use as a Risk Factor for Schizophrenia in
Swedish Conscripts of 1969,” British Medical Jour-
nal 325 (2002); Henquet et al., “Prospective Cohort
Study of Cannabis Use, Predisposition for Psycho-
sis, and Psychotic Symptoms in Young People,”
British Medical Journal (December 2004); Gold-
berg, “Studies Link Psychosis, Teenage Marijuana
Use,” Boston Globe, January 26, 2006; Shulman,
“Marijuana Linked to Heart Disease and Depres-
sion,” U.S. News, May 14, 2008.
See also Jan C. van Ours et al., “Cannabis Use
and Suicidal Ideation,” Journal of Health Economics
32, no. 3 (2013): 524–37; Jan C. van Ours and Jenny
Williams, “The Effects of Cannabis Use on Physi-
cal and Mental Health,” Journal of Health Econom-
ics 31, no. 4 (July 2012): 564–77; Jan C. van Ours and
Jenny Williams, “Cannabis Use and Mental Health
Problems,” Journal of Applied Econometrics 26, no. 7
(November 2011): 1137–56; and Jenny Williams and
Christopher L. Skeels, “The Impact of Cannabis
Use on Health,” De Economist 154, no. 4 (December
2006): 517–46.
51. National Institute on Drug Abuse, “What Are
Marijuana’s Long-Term Impacts on the Brain?”
Research Report Series, March 2016, https://www.
drugabuse.gov/publications/research-reports/mar
ijuana/how-does-marijuana-use-affect-your-brain-
body. Kelly and Rasul evaluate the depenalization
of marijuana in a London borough and find large in-
creases in hospital admissions related to hard drug
use, particularly among younger men. See Elaine
Kelly and Imran Rasul, “Policing Cannabis and
Drug Related Hospital Admissions: Evidence from
Administrative Records,” Journal of Public Economics
112 (April 2014): 89–114.
52. “Detailed Mortality Statistics,” Centers for Dis-
ease Control and Prevention, WONDER Online
Databases, http://wonder.cdc.gov/.
53. Ibid.
54. The link between medical marijuana and low-
er suicide rates may stem partly from the fact that
medical marijuana can substitute for other, more
dangerous painkillers and opiates. Research by
Anne Case and Angus Deaton found suicides and
drug poisonings led to a marked increase in mor-
tality rates of middle-aged white non-Hispanic
men and women in the United States between
1999 and 2013. Other studies have linked opioid
and painkiller overdoses to a recent surge in self-
inflicted drug-related deaths and suicides. Medi-
cal marijuana, as a less risky pain reliever, may thus
help lessen the rate of drug deaths and suicides.
For more, see Case and Deaton, “Rising Morbid-
ity and Mortality in Midlife among White Non-
Hispanic Americans in the 21st Century,” National
Academy of Sciences 112, no. 49 (November 2015),
http://www.pnas.org/content/112/49/15078.
55. Kevin Wong and Chelsey Clarke, The Legal-
ization of Marijuana in Colorado: The Impact Vol. 3
(Denver: Rocky Mountain High Intensity Drug
Trafficking Area, September 2015), http://www.
rmhidta.org/html/2015%20final%20legaliza
tion%20of%20marijuana%20in%20colorado
%20the%20impact.pdf.
56. Caleb Banta-Green et al., “Drug Abuse
32
Trends in the Seattle-King Country Area: 2014,”
Report, University of Washington Alcohol and
Drug Abuse Institute, Seattle, June 17, 2015,
http://adai.washington.edu/pubs/cewg/Drug%20
Trends_2014_final.pdf.
57. David Musto, “Opium, Cocaine and Marijua-
na in American History,” Scientific American, no. 1
(July 1991): 40–47, http://www.ncbi.nlm.nih.gov/
pubmed/1882226.
58. U.S. Drug Enforcement Administration, “The
Dangers and Consequences of Marijuana Abuse,”
U.S. Department of Justice, Washington, May
2014, p. 24, https://www.dea.gov/docs/dangers-con
sequences-marijuana-abuse.pdf.
59. For example, Sheriff David Weaver of Douglas
County, Colorado, warned in 2012, “Expect more
crime, more kids using marijuana, and pot for sale
everywhere.” See Matt Ferner, “If Legalizing Mari-
juana Was Supposed to Cause More Crime, It’s Not
Doing a Very Good Job,” The Huffington Post, July 17,
2014, http://www.huffingtonpost.com/2014/07/17/
marijuana-crime-denver_n_5595742.html.
60. Jeffrey Miron, “Marijuana Policy in Colorado,”
Cato Institute Working Paper, October 23, 2014,
http://object.cato.org/sites/cato.org/files/pubs/pdf/
working-paper-24_2.pdf.
61. “Marijuana Is Safer Than Alcohol: It’s Time
to Treat It That Way,” Marijuana Policy Project,
Washington, https://www.mpp.org/marijuana-is-
safer/. See also Peter Hoaken and Sherry Stewart,
“Drugs of Abuse and the Elicitation of Human
Aggressive Behavior,” Addictive Behaviors 28:
(2003): 1533–54, http://www.ukcia.org/research/
AgressiveBehavior.pdf.
62. Denver Police Department, Uniform Crime
Reporting Program, “Monthly Citywide Data—
National Incident-Based Reporting System,” http://
www.denvergov.org/police/PoliceDepartment/Crime
Information/CrimeStatisticsMaps/tabid/441370/
Default.aspx.
63. Fort Collins crime data yield similar factual
conclusions, showing no consistent rise in crime
following either the November 2012 legalization
or the January 2014 opening of stores.
64. “Crime Dashboard,” Seattle Police Depart-
ment, http://www.seattle.gov/seattle-police-depart
ment/crime-data/crime-dashboard.
65. Sierra Rayne, “Seattle’s Post-Marijuana Legal-
ization Crime Wave,” American Thinker, Novem-
ber 13, 2015, http://www.americanthinker.com/
blog/2015/11/seattles_postmarijuana_legalization_
crime_wave.html.
66. Elsewhere in Washington State, this conclu-
sion seems equally robust. Tacoma, a large city
in northeastern Washington where stores have
opened, has generally seen stable crime trends be-
fore and after legalization. Total monthly offens-
es, violent crime, and property crime have shown
no significant deviation from their recent trends.
See Kellie Lapczynski, “Tacoma Monthly Crime
Data,” Washington Association of Sheriffs and
Police Chiefs, 2015, p377–78, http://www.waspc.
org/assets/CJIS/crime%20in%20washington%20
2015.small.pdf.
67. “City of Portland—Neighborhood Crime Sta-
tistics,” Portland Police Bureau, http://www.port
landonline.com/police/crimestats/.
68. In Salem, Oregon, violent crime, property
crime, and drug offenses show no significant jumps
post-legalization. Although Salem is farther from
the border with Washington, there are no indica-
tions of major spillover effects between 2012 and
2014. See Linda Weber, “Monthly Crime Statistics,”
Salem Police Department, 2015, http://www.cityof
salem.net/Departments/Police/HowDoI2/Pages/
CrimeStatistics.aspx. Alaska is not covered in this
section because reliable recent crime data for major
Alaskan cities were unavailable at the time of writing.
69. For a review of this issues, see Rune Elvik,
“Risk of Road Accident Associated with the Use
of Drugs: A Systematic Review and Meta-Anal-
ysis of Evidence from Epidemiological Studies,”
Accident Analysis and Prevention 60 (2013): 254–67,
33
doi:10.1016/j.aap.2012.06.017, http://www.ncbi.
nlm.nih.gov/pubmed/22785089.
70. Academic studies examining this issue have
suggested a possible substitution effect. A 2015
report by the Governors Highway Safety Organi-
zation cited one study revealing that marijuana-
positive fatalities rose by 4 percent after legaliza-
tion in Colorado. However, another study from
the same report discovered no change in total
traffic fatalities in California after its decriminal-
ization of the drug in 2011. See also Andrew Sewell
et al., “The Effect of Cannabis Compared with Al-
cohol on Driving,” American Journal on Addictions
18, no. 3 (2009): 185–93, http://www.ncbi.nlm.nih.
gov/pmc/articles/PMC2722956/.
71. Kevin A. Sabet, “Colorado Will Show Why
Legalizing Marijuana Is a Mistake,” Washington
Times, January 17, 2014, http://www.washington
times.com/news/2014/jan/17/sabet-marijuana-legal
izations-worst-enemy/.
72. Associated Press, “Fatal Crashes Involving
Marijuana Doubled in Washington after Legaliza-
tion,” The Oregonian, August 20, 2015, http://www.
oregonlive.com/marijuana/index.ssf/2015/08/fa-
tal_crashes_involving_mariju.html.
73. Noelle Phillips and Elizabeth Hernandez,
“Colorado Still Not Sure Whether Legal Marijua-
na Made Roads Less Safe,” Denver Post, December
29, 2015, http://www.denverpost.com/2015/12/29/
colorado-still-not-sure-whether-legal-marijuana-
made-roads-less-safe/.
74. Radley Balko, “Since Marijuana Legaliza-
tion, Highway Fatalities in Colorado Are at Near-
Historic Lows,” Washington Post, August 5, 2014,
https://www.washingtonpost.com/news/the-watch/
wp/2014/08/05/since-marijuana-legalization-high
way-fatalities-in-colorado-are-at-near-historic-lows/.
75. These data include any kinds of crashes on all
types of roads, as recorded by each state’s depart-
ment of transportation. See Colorado Department
of Transportation’s “Fatal Accident Statistics by
City and County,” http://www.coloradodot.info/
library/traffic/traffic-manuals-guidelines/safety-
crash-data/fatal-crash-data-city-county/fatal-
crashes-by-city-and-county.
76. Annual crash data from the National Highway
Traffic Safety Administration (NHTSA) confirm
these findings. Our analysis uses state-level traffic
accident data from individual state transporta-
tion departments because their data are mostly
reported monthly and have a shorter reporting
time lag than NHTSA data. For NHTSA data,
see “State Traffic Safety Information,” NHTSA,
http://www-nrd.nhtsa.dot.gov/departments/nrd-
30/ncsa/STSI/8_CO/2014/8_CO_2014.htm.
77. We additionally analyzed fatality rates for acci-
dents involving alcohol impairment. Similarly, this
time series shows no clear signs of significant swings
after marijuana policy changes, suggesting that any
substitution effect associated with marijuana has
been small compared to overall drunk driving.
78. Washington Traffic Safety Commission, 2015,
http://wtsc.wa.gov/research-data/crash-data/.
79. Washington State police routinely test drivers
involved in car crashes for traces of various sub-
stances. The official legalization of marijuana use at
the end of 2012 appears to have had at most a neg-
ligible effect on crash fatalities. The Washington
Traffic Safety Commission recorded a total of 62
marijuana-related crash fatalities in 2013, compared
to 61 in 2012. There does seem to be a temporary
increase in fatalities caused by marijuana-related
crashes around the same time as the establishment
of Washington’s first marijuana shops. Neverthe-
less, any sort of spike seems to have been tempo-
rary. In the first six months following the opening
of stores, 46 crash fatalities were tied to using mari-
juana while driving; over the following six months,
that number dropped to 32.
80. Monthly data on fatal crashes themselves
were not available. Monthly 2015 data were also
not available at the time of writing.
81. For instance, Meier et al. analyze a large sample
of individuals tracked from birth to age 38 and find
34
that those who smoked marijuana most heavily
prior to age 18 lost an average of eight IQ points, a
highly significant drop. See Madeline Meier et al.,
“Persistent Cannabis Users Show Neuropsycho-
logical Decline from Childhood to Midlife,” Pro -
ceedings of the National Academy of Sciences 109, no.
40 (2012): E2657–E2664, http://www.ncbi.nlm.
nih.gov/pubmed/22927402.
However, other studies have found results that
rebut Meier et al. Mokrysz et al. examine an even
larger sample of adolescents and, after control-
ling for many potentially confounding variables,
discover no significant correlation between teen
marijuana use and IQ change. See Claire Mokrysz
et al., “Are IQ and Educational Outcomes in Teen-
agers Related to Their Cannabis Use? A Prospective
Cohort Study,” Journal of Psychopharmacology 30,
no. 2 (2016): 159–68, http://jop.sagepub.com/con
tent/30/2/159.
82. Cobb-Clark et al. show that much of relation-
ship between marijuana use and educational out-
comes is likely due to selection, although there is
possibly some causal effect in reducing university
entrance scores. See Deborah A. Cobb-Clark et
al., “‘High’-School: The Relationship between
Early Marijuana Use and Educational Outcomes,”
Economic Record 91, no. 293 (June 2015): 247–66.
Evidence in McCaffrey et al. supports this selec-
tion explanation of the association between mari-
juana use and educational outcomes. See Daniel F.
McCaffrey et al., “Marijuana Use and High School
Dropout: The Influence of Unobservables,” Health
Economics 19, no. 11 (November 2010): 1281–99.
Roebuck et al. suggest that chronic marijuana
use, not more casual use, likely drives any relation-
ship between marijuana use and school attendance.
See M. Christopher Roebuck et al., “Adolescent
Marijuana Use and School Attendance,” Economics
of Education Review 23, no. 2 (2004), 133–41.
Marie and Zölitz estimate grade improvements
are likely due to improved cognitive functioning
among students whose nationalities prohibited
them from consuming marijuana. See Olivier Marie
and Ulf Zölitz, “‘High’ Achievers? Cannabis Access
and Academic Performance,” CESifo Working Pa-
per Series no. 5304, Center for Economic Studies
and Ifo Institute, Munich, 2015.
Van Ours and Williams review the literature
concluding that cannabis may reduce educational
outcomes, particularly with early onset of use. See
Jan van Ours and Jenny Williams, “Cannabis Use
and Its Effects on Health, Education and Labor
Market Success,” Journal of Economic Surveys, 29,
no. 5 (December 2015): 993–1010.
For additional evidence on likely negative effects
of early onset of use see also Paolo Rungo et al., “Pa-
rental Education, child’s grade repetition, and the
modifier effect of cannabis use,” Applied Econom-
ics Letters 22(3)(2015): 199-203; Jan C. van Ours and
Jenny Williams, “Why Parents Worry: Initiation
into Cannabis Use by Youth and Their Educational
Attainment,” Journal of Health Economics 28, no. 1
(2009): 132–42; and Pinka Chatterji, “Illicit Drug
Use and Educational Attainment,” Health Economics
15, no. 5 (2006): 489–511.
83. “Suspension/Expulsion Statistics,” Colorado
Department of Education, 2015, http://www.cde.
state.co.us/cdereval/suspend-expelcurrent.
84. “Washington State Report Card, 2013–14 Re-
sults,” Washington State Office of the Superin-
tendent of Public Instruction, http://reportcard.
ospi.k12.wa.us/summary.aspx?groupLevel=Distr
ict&schoolId=1&reportLevel=State&year=2013-
14&yrs=2013-14.
85. Sarah Berger, “Colorado’s Marijuana Indus-
try Has a Big Impact on Denver Real Estate:
Report,” International Business Times, October 20,
2015, http://www.ibtimes.com/colorados-marijua-
na-industry-has-big-impact-denver-real-estate-
report-2149623.
86. “S&P/Case-Schiller Denver Home Price In-
dex,” S&P Dow Jones Indices, http://us.spindices.
com/indices/real-estate/sp-case-shiller-co-denver-
home-price-index/.
87. U.S. Department of Commerce, Bureau of
Economic Analysis, http://www.bea.gov/iTable/
iTable.cfm?reqid=70&step=1&isuri =1&acrdn=1#
reqid=70&step=30&isuri=1&7022=36&7023=0&7
024=non-indust3000&7027=1&7001=336&7028=-
&7031=0&7040=-083=levels&7029=36&7090=70.
35
88. As an example, Oregon state legislator Ann
Lininger wrote an op-ed predicting a “jobs
boom” in southern Oregon after marijuana le-
galization. See Lininger, “Marijuana: Will Le-
galization Create an Economic Boom?” The
Huffington Post. October 1, 2015. http://www.
huffingtonpost.com/ann lininger/marijuana-
will-legalizati_b_8224712.html.
89. “Local Area Unemployment Statistics,” Bureau
of Labor Statistics, http://www.bls.gov/lau/.
90. U.S. Department of Commerce, Bureau of
Economic Analysis, http://www.bea.gov/iTable/
iTa blecfm?reqid=70&step=1&isuri=1&acrdn=1#r
eqid=70&step=10&isuri=1&7003=200&7035=-.
91. Colorado Department of Revenue, “Colorado
Marijuana Tax Data,” Colorado Official State Web
Portal, https://www.colorado.gov/pacific/revenue/
colorado-marijuana-tax-data.
92. Tom Robleski, “Up in Smoke: Colorado Pot
Biz Not the Tax Windfall Many Predicted,” Janu-
ary 2015, http://www.silive.com/opinion/columns/
index.ssf/2015/01/up_in_smoke_colorado_pot_
biz_n.html.
93. Washington State Department of Revenue,
“Marijuana Tax Tables,” http://dor.wa.gov/Content/
AboutUs/StatisticsAndReports/stats_MMJTaxes.
aspx and http://www.502data.com/.
94. “Washington Rakes in Revenue from
Marijuana Taxes,” RT (Russia Today televi-
sion channel), July 13, 2015, https://www.rt.com/
usa/273409-washington-state-pot-taxes/.
95. Oregon Department of Revenue, “Marijuana
Tax Program Update,” Joint Interim Committee
on Marijuana Legalization, May 23, 2016, https://
olis.leg.state.or.us/liz/2015I1/Downloads/Com-
mit teeMeetingDocument/90434.
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www.thelancet.com/psychiatry Vol 2 July 2015 601
Articles
Medical marijuana laws and adolescent marijuana use in
the USA from 1991 to 2014: results from annual, repeated
cross-sectional surveys
Deborah S Hasin, Melanie Wall, Katherine M Keyes, Magdalena Cerdá, John Schulenberg, Patrick M O’Malley, Sandro Galea, Rosalie Pacula,
Tianshu Feng
Summary
Background Adolescent use of marijuana is associated with adverse later eff ects, so the identifi cation of factors
underlying adolescent use is of substantial public health importance. The relationship between US state laws that
permit marijuana for medical purposes and adolescent marijuana use has been controversial. Such laws could convey
a message about marijuana acceptability that increases its use soon after passage, even if implementation is delayed
or the law narrowly restricts its use. We used 24 years of national data from the USA to examine the relationship
between state medical marijuana laws and adolescent use of marijuana.
Methods Using a multistage, random-sampling design with replacement, the Monitoring the Future study conducts
annual national surveys of 8th, 10th, and 12th-grade students (modal ages 13–14, 15–16, and 17–18 years, respectively),
in around 400 schools per year. Students complete self-administered questionnaires that include questions on
marijuana use. We analysed data from 1 098 270 adolescents surveyed between 1991 and 2014. The primary outcome
of this analysis was any marijuana use in the previous 30 days. We used multilevel regression modelling with
adolescents nested within states to examine two questions. The fi rst was whether marijuana use was higher overall in
states that ever passed a medical marijuana law up to 2014. The second was whether the risk of marijuana use
changed after passage of medical marijuana laws. Control covariates included individual, school, and state-level
characteristics.
Findings Marijuana use was more prevalent in states that passed a medical marijuana law any time up to 2014 than in
other states (adjusted prevalence 15·87% vs 13·27%; adjusted odds ratio [OR] 1·27, 95% CI 1·07–1·51; p=0·0057).
However, the risk of marijuana use in states before passing medical marijuana laws did not diff er signifi cantly from
the risk after medical marijuana laws were passed (adjusted prevalence 16·25% vs 15·45%; adjusted OR 0·92,
95% CI 0·82–1·04; p=0·185). Results were generally robust across sensitivity analyses, including redefi ning marijuana
use as any use in the previous year or frequency of use, and reanalysing medical marijuana laws for delayed eff ects or
for variation in provisions for dispensaries.
Interpretation Our fi ndings, consistent with previous evidence, suggest that passage of state medical marijuana laws
does not increase adolescent use of marijuana. However, overall, adolescent use is higher in states that ever passed
such a law than in other states. State-level risk factors other than medical marijuana laws could contribute to both
marijuana use and the passage of medical marijuana laws, and such factors warrant investigation.
Funding US National Institute on Drug Abuse, Columbia University Mailman School of Public Health, New York
State Psychiatric Institute.
Introduction
In the USA, adolescent marijuana use has increased
since the mid-2000s.1,2 Adolescent use, especially regular
use, is associated with increased likelihood of harmful
eff ects, including short-term impairments in memory,
coordination, and judgment, and longer-term risks of
altered brain development, cognitive impairments,3–5
unemployment,6 psychiatric symptoms and substance
addiction.1,7 Therefore, identifi cation of factors underlying
adolescent use is of substantial importance. To aff ect
prevalence nationally, factors must aff ect wide segments
of the population; state laws permitting the use of
marijuana for medical purposes have been proposed as
one such factor.8–10 Since 1996, 23 US states and the
District of Columbia have passed medical marijuana
laws, and other states are considering such laws. Although
the specifi c provisions of state medical marijuana laws
diff er,11 they all have a common purpose: to legalise the
use of marijuana for medical purposes. However, by
conveying a message about acceptability or an absence of
harmful health consequences, passage of such laws could
aff ect youth perception of harms, leading to increased
prevalence of marijuana use in the years immediately
after the law has passed, even with delayed implementation
or narrow limits on use.
Whether medical marijuana laws are associated with
increased use of marijuana by adolescents has been
debated. Some commentators have suggested that these
Lancet Psychiatry 2015;
2: 601–08
Published Online
June 16, 2015
http://dx.doi.org/10.1016/
S2215-0366(15)00217-5
See Comments page 572
See Online for a podcast
interview with Deborah Hasin
Department of Epidemiology
(Prof D S Hasin PhD,
K M Keyes PhD, M Cerdá Dr PH,
Prof S Galea MD) and
Department of Biostatistics
(Prof M Wall PhD), Mailman
School of Public Health,
Columbia University, New York,
NY, USA; Department of
Psychiatry, Columbia
University Medical Center,
New York, NY, USA
(Prof D S Hasin, Prof M Wall);
New York State Psychiatric
Institute, New York, NY, USA
(Prof D S Hasin, Prof M Wall);
Research Foundation of Mental
Hygiene, New York, NY, USA
(T Feng MS); Department of
Psychology
(Prof J Schulenberg PhD) and
Institute for Social Research
(Prof J Schulenberg,
Prof P M O’Malley PhD),
University of Michigan,
Ann Arbor, MI, USA; RAND
Corporation, Santa Monica, CA,
USA (Prof R Pacula PhD); and
National Bureau of Economic
Research, Cambridge, MA, USA
(Prof R Pacula)
Correspondence to:
Prof Deborah Hasin, Department
of Psychiatry, Columbia
University Medical Center,
New York, NY 10032, USA
deborah.hasin@gmail.com
Articles
602 www.thelancet.com/psychiatry Vol 2 July 2015
laws have no eff ect, or actually discourage use.12,13 Others
suggest that these laws increase adolescent use of
marijuana through various mechanisms,8 such as
sending a message that use is acceptable.9,10 In 2013, 19%
of high school seniors (generally aged 17 and 18 years)
reported that they would try marijuana or use it more
often if it were legalised for general use.14 In a study of
adolescents in paediatric practices in states that had not
passed medical marijuana laws,15 55% thought that
passing such a law would “make it easier for teens to
start to smoke marijuana for fun”. These fi ndings
suggest that the legal status of marijuana, including
medical marijuana laws, could increase adolescent use of
marijuana.
Previously, we showed that adolescent16 and adult17
marijuana use was more prevalent in US states with
medical marijuana laws than in states without such laws.
However, we examined only fairly short periods, and the
studies did not address whether this increased prevalence
preceded or followed passage of the law.18,19 One study
suggested that after 2009, a confl uence of federal and
local factors predicted greater adolescent marijuana use
in Colorado, a state with a medical marijuana law, than in
39 other states without such laws.20 Other studies (of
four21 and fi ve states;22 seven states in total because of
overlap) did not show increased adolescent use after
medical marijuana laws were passed. All these studies
were limited by the small sample sizes, the few states
included with medical marijuana laws, and years
examined, leaving questions about whether the absence
of eff ect might be due to insuffi cient statistical power or
the particular states studied. Examination of a greater
number of participants, years, and states should more
defi nitively establish whether the passage of medical
marijuana laws predicts a subsequent increase in
adolescent marijuana use.
We therefore examined the relationship between state
medical marijuana laws and adolescent marijuana use
using 24 years of yearly survey data (1991–2014) from
repeated annual, cross-sectional surveys that included
more than 1 million adolescents in the 48 contiguous
states, of which 21 had passed medical marijuana laws
Research in context
Evidence before this study
If passage of a state law legalising marijuana for medical use
conveyed a public message to adolescents that marijuana use
was acceptable or did not lead to adverse eff ects, this law could
quickly increase adolescent use of marijuana, even if the law was
implemented slowly or had provisions that tightly restricted
marijuana use. To identify studies relevant to this issue, we
searched PubMed for English-language articles with the term,
“medical marijuana”. As of April 6, 2015, 449 articles with this
term were published, the fi rst in 1978, and all the rest since
1994. Most articles were opinion pieces about the pros and cons
of medical marijuana use, regarding either its medicinal
benefi ts, or implications for society. To be considered relevant to
the present study, we reviewed reports with empirical fi ndings
that were based on general-population surveys with state-based
samples, had marijuana use as an outcome, and compared
states with and without medical marijuana laws, or states
before and after passage of such laws. We identifi ed two reports
showing overall higher rates of marijuana use in states with
medical marijuana laws, one in adolescents and the other in
adults, with one replication of the adolescent result. Comparison
of Colorado, a state with a medical marijuana law, with states
without medical marijuana laws found suggestive but
inconclusive evidence regarding the eff ects of the law on
adolescent marijuana use. Two studies, that in combination
examined seven states that passed medical marijuana laws did
not show increased prevalence of adolescent marijuana use after
the laws were passed, relative to the prevalence before the laws
were passed. However, limitations in the number of states
examined, number of years, and sample sizes left unclear
whether the absence of diff erences in marijuana use pre-law and
post-law were real or due to limitations of the methods.
Added value of this study
Our study, which included data from annual national surveys
spanning 24 years (1991–2014) for 1 098 270 adolescents in
48 US states, provides two pieces of defi nitive evidence about
medical marijuana laws and adolescent use of marijuana.
First, across all survey years, overall adolescent marijuana use
was higher in states that had ever passed medical marijuana
laws than in states that did not have these laws, but the
increased use was present in states both before and after the
laws were passed. Second, our comprehensive study showed
no evidence for an increase in adolescent use of marijuana in
the year of passage of a medical marijuana law, or in the fi rst
or second years after passage. These results were consistent
across several sensitivity analyses that used a diff erent
defi nition of the marijuana outcome variable, that removed
one state at a time from the sample to establish whether one
state was unduly aff ecting the overall results (none did), or
whether a state medical marijuana law provided for
dispensaries.
Implications of all the available evidence
Our two main fi ndings, in conjunction with other evidence,
suggest that state-level factors other than medical marijuana
laws infl uence adolescent marijuana use. Because both
human studies and animal models show that early adolescent
use of marijuana increases the risk of important adverse
eff ects in adulthood, the identifi cation of large-scale societal
factors that increase the risk of early use is crucial. Our study
fi ndings suggest that the debate over the role of medical
marijuana laws in adolescent marijuana use should cease, and
that resources should be applied to identifying the factors
that do aff ect risk.
Articles
www.thelancet.com/psychiatry Vol 2 July 2015 603
by 2014 (fi gure 1). Controlling for individual-level,
school-level, and state-level factors, we addressed two
questions. The fi rst was whether adolescents were
generally at higher risk for marijuana use in states that
ever passed a medical marijuana law by 2014 than
adolescents in other states. This question extends our
previous work16,17 by greatly increasing the number of
years considered and controlling for potentially
important state and individual covariates. The second
question was whether adolescents in states that had
passed medical marijuana laws were at higher risk of
marijuana use in the years immediately after passage of
the law than adolescents in those states before passage
of the law.
Methods
Study design and participants
Since 1991, the Monitoring the Future study has conducted
national, annual cross-sectional surveys of adolescents in
school grades 8, 10, and 12 (modal ages 13–14, 15–16, and
17–18 years, respectively), in about 400 schools each year
(mean schools per year 409·3 [SD 17·34]; range 377–435
schools per year) in the 48 contiguous US states.
Monitoring The Future surveys use a multistage, random
sampling design with replacement. The stages include
geographical area, schools within area (with probability
proportionate to school size), and students within school.
Up to 350 students per grade, per school are included,
with classrooms randomly selected within schools.
Schools participate for two consecutive years. Non-
participating schools are replaced with others matched for
location, size, and urbanicity.
Data were collected from students via self-administered
questionnaires.23 Measures24 and data collection pro-
cedures have remained consistent across years.14 Students
completed questionnaires in classrooms or larger
group administrations. Monitoring the Future study re-
presentatives distributed and collected question naires
using standardised procedures to maintain con fi dentiality.14
Self-administered forms and the data collection procedures
are designed to maximise the validity of substance use
reporting. Low quantities of non-responses, high pro-
portions of students consistently reporting illicit drug use,
and strong construct validity have previously been reported
for the Monitoring the Future study.21
Advance notice to parents and students about the study
included that participation was voluntary and responses
were either anonymous (for 8th and 10th graders) or
confi dential (for 12th graders; responses of 12th graders
are not anonymised so that they can participate in follow-
up studies).14 All Monitoring the Future study procedures
were reviewed and approved by the University of
Michigan Institutional Review Board.14
Measures
The primary outcome was any marijuana use within the
previous 30 days versus no use, a binary individual-level
variable previously used in time-trend analysis of
Monitoring the Future data.25 We also examined any
marijuana use within the past 12 months, similarly
dichotomised, in sensitivity analyses.
Our main exposure was “state-level medical marijuana
law”, represented in the analysis by two state-level
variables. The fi rst was a binary variable that showed
whether a state passed a medical marijuana law by 2014
(21 had passed such laws), irrespective of the year that it
passed. We used this variable to compare risk of
adolescent marijuana use in states that had ever passed a
medical marijuana law with risk in states that had not.
The second was a time-varying binary variable for each
year (1991–2014) and state (48 states) indicating whether
the state had passed a medical marijuana law that year or
not, as established through review of state policies by
legal scholars, economists, and policy analysts at the
RAND Corporation.11 We defi ned the variable for state–
year as the year that the law was passed (appendix p 1).
This variable enabled us to examine adolescents within
states before and after passage of medical marijuana
laws, in conjunction with adolescents in states that never
passed a medical marijuana law.
States that have passed medical marijuana laws
permitting medical marijuana dispensaries might diff er
from states whose medical marijuana laws do not permit
dispensaries in terms of marijuana availability, public
perceptions, and potency.26 We therefore explored an
alternative defi nition11 of our yearly state medical
marijuana law variable, re-coding it as a three-level
variable: no medical marijuana law, a medical marijuana
law not permitting dispensaries, and a medical marijuana
law permitting dispensaries. The latter category was
defi ned as implicitly permitting dispensing via caregivers
and amounts per patient, or explicit acknowledgment of
dispensaries as either permitted or not declared illegal
(p 1 of the appendix shows the years that states were
coded positive by this defi nition).
See Online for appendix
Figure 1: US states with medical marijuana laws as of 2014, and years of passage
WA
OR
NV
(2000)
CA
(1996)
AZ
(2010) NM
(2007)
CO
(2000)
MT
(2004)
IL
(2013)
MI
(2008)
ME
(1999)
ID
WY
UT
ND
SD
NE
KS
OK
TX
IA
MO
AR
LA
MS
AL
TN
NC
VA
WV
PA
NY
(2014)
OH
IN
KY
SC
GA
FL
MN
(2014)
WI
NH
(2013)
VT
(2004)
MA
(2012)
RI
(2006) CT
(2012)
NJ
(2010) DE
(2006)
MD
(2003)
(1998)
(1998)
States with medical marijuana laws
For Monitoring the Future see
www.monitoringthefuture.org
Articles
604 www.thelancet.com/psychiatry Vol 2 July 2015
School-level control variables included the number of
students per grade within school; public versus private
school; and urban or suburban (ie, within metropolitan
statistical areas)27 versus rural schools. State-level control
variables included the proportion of each state’s population
who were male, white, aged 10–24 years, and older than
25 years without high-school education. We used US
census values from 1990, 2000, and 2010 for survey years
1991–95, 1996–2005, and 2006–14, respectively.
Individual covariates included age, gender, ethnic
origin (white, black, Hispanic, Asian, mixed, and other),
grade (when combining grades), and socioeconomic
status (highest parental education categorised as high
school not completed, high-school graduate or equivalent,
some university education, or a 4-year university degree
or higher).
Statistical analysis
We conducted multilevel logistic regression modelling of
adolescents nested within states to address whether
marijuana use was higher overall in states that passed a
medical marijuana law at any point between 1991 and
2014 than in other states; and whether the risk of
marijuana use changed after a medical marijuana law
was passed compared with the risk before the law passed,
controlling for the contemporaneous risk of use overall
in other states (appendix pp 6 and 7). For these analyses,
we used SAS Proc Glimmix code (version 9.4). We
controlled for the non-linear historical trend in marijuana
use across the 24 years with a piece-wise cubic spline.
Covariates at an individual, school, and state level were
controlled (appendix pp 6 and 7). We fi tted a single
multilevel model to the entire study dataset that
simultaneously addressed both research questions
through specifi cation of the two primary predictors:
a dichotomous indicator of whether a state passed a
medical marijuana law any time between 1991 and 2014,
coded 1 for all individuals in the states with a law before
2014 (irrespective of year passed) and 0 for all others; and
a time-varying indicator coded 0 for individuals in states
in the years before a medical marijuana law passed
(including states with no medical marijuana laws before
2014) and 1 for individuals in states in the years during
and after the law passed). The time-varying indicator
provides a diff erence-in-diff erence estimator of change
in risk due to marijuana laws in which the contrast is
between the average within-state change in risk of use
before versus after the law passed, compared with the
aggregated contemporaneous average change in risk of
use in states that do not pass such a law. We fi rst fi tted
the multilevel model combining 8th, 10th, and
12th grades, and then refi tted the model including and
testing an interaction with grade to obtain grade-specifi c
medical marijuana law eff ects. The latter was done
because the prevalence of marijuana use diff ers by grade,
and thus risk factors could diff er as well.
We present adjusted odds ratios (ORs) and 95% CIs for
the combined and grade-specifi c eff ects, and state-
specifi c log OR estimates (pre-law vs post-law) for the
21 states that passed such laws. We derived adjusted
prevalence estimates aggregated for the states with and
without medical marijuana laws for each year from the
multilevel logistic model, aggregating across years and
also plotted by year. State-specifi c log OR estimates in the
post-passage years compared with the pre-passage years
are presented for the 21 states that passed laws.
Estimation and testing of the state-level predictors
with the multilevel model did not require inclusion of
sampling weights, because the model directly in-
corporated all individual-level and school-level variables
related to the sampling design.28 Within the Monitoring
the Future study, not all states had data available for
every year and grade; the multilevel model addresses
this diffi culty by smoothing eff ects across missing years
and grades with state-level random eff ects (allowing for
the eff ects of covariates—eg, ethnic origin—to vary by
state). We used multiple imputation (Proc MI, SAS
version 9.4) at the individual level to handle missing
covariate data (range 2·98% [age] to 8·05% [parental
education]; appendix pp 2, 6).
We conducted fi ve sets of sensitivity analyses to
determine the robustness of the fi ndings. First, the
binary marijuana use variable was replaced with an
ordered categorical outcome indicating frequency of
past-month use (0, 1–2, 3–5, 6–9, 10–19, 20–39, or 40 +
occasions), modelled with cumulative odds. Second, the
time-varying variable indicating medical marijuana law
was re-coded as positive in three diff erent ways to allow
for delayed eff ects (lag) between passage of the law and
changes in population behaviour: recoding the state–
year variable positive starting the year following passage
Adjusted prevalence Adjusted odds
ratio (95% CI)
p value
Medical
marijuana
law passed
by 2014
Medical
marijuana
law not passed
by 2014
Combined grades 15·87% 13·27%1·27 (1·07–1·51)0·0057
8th grade 7·22% 6·95%1·18 (0·98–1·44)0·0871
10th grade 18·02% 15·04%1·23 (1·01–1·49)0·0352
12th grade 22·36% 17·83%1·35 (1·11–1·63)0·0024
Table shows marijuana use in the previous 30 days. Modal ages of students:
8th grade 13–14 years; 10th grade 15–16 years; 12th grade 17–18 years. Adjusted
prevalences encompassing years 1991 to 2014 were derived from the multilevel
model, with distributions of covariates fi xed at grade-specifi c overall US
distributions averaged across all 24 years. The model controlled for sex, age, race,
education of parents, class size, whether educated at an urban or rural school,
public or private school, and state-aggregated percentage who were male,
percentage who were white, percentage with no high school education, and
percentage aged 11–24 years. The model also included a state random intercept,
and state-specifi c cubic spline polynomials to control for trend with a knot at the
years 1998 and 2006. See appendix p 4 for absolute numbers.
Table 1: Adolescent use of marijuana in the 48 US contiguous states
between 1991 and 2014
Articles
www.thelancet.com/psychiatry Vol 2 July 2015 605
if the medical marijuana law was passed after July;
recoding the variable as positive in the year following
passage for all states with medical marijuana laws;
recoding the variable as positive 2 years following
passage for all states with medical marijuana laws
(appendix p 7). Third, we replaced the binary state–year
law variable with the three-level dispensary variable.
Fourth, we replaced use in the past month with use in
the past year. Fifth, to ensure that no state unduly
infl uenced the results, the multilevel model was refi tted
48 times, removing one state each time. Sensitivity
analyses used a model that combined eff ects across
grades, and a model with grade-by-law interaction to
identify grade-specifi c eff ects.
Role of the funding source
The funders of the study had no role in study design,
data collection, data analysis, data interpretation, or
writing of the report. The corresponding author had full
access to all the data in the study and had fi nal
responsibility for the decision to submit for publication.
Results
By 2014, 21 of the 48 contiguous states had passed a
medical marijuana law (fi gure 1, appendix p 1). Across
the 21 states, the mean number of years since the law
was passed was 6·76 (SD 6·06), and the median number
of years was 4·0 (see appendix, p 7 for more detail).
Between 1991 and 2014, the Monitoring the Future
study surveyed a total of 1 134 734 (408 942 in 8th grade,
370 449 in 10th grade, and 355 343 in 12th grade). After we
excluded students who were missing marijuana data,
1 098 270 (96·8%) remained for analysis: 396 310 8th
graders (96·9%), 361 400 10th graders (97·6%), and
340 560 12th graders (95·8%). Of all selection sample
units, 95–99% obtained one or more participating
schools in all study years. Previous studies have shown
no time trend in school participation.29 Student response
rates were 81–91% for almost all years and grades (mean
response rates for 1991–2013). Most non-responses were
because of absenteeism; less than 1% of students
declined participation in the survey when asked in the
school to complete the questionnaire.
Marijuana use in the previous 30 days was more
prevalent in states that passed a medical marijuana law
between 1991 and 2014 than in those that had not
(adjusted prevalence 15·87% vs 13·27%; adjusted
OR 1·27, 95% CI 1·07–1·51, p=0·0057). This fi nding did
not diff er by grade (table 1; interaction of grade and state
medical marijuana law status, p=0·33). This eff ect,
aggregated across years before and after passage of
marijuana laws, suggests that, overall, states with a
medical marijuana law had an increased prevalence of
marijuana use even before the law was passed (fi gure 2).
Aggregating across grade, the risk of marijuana use did
not signifi cantly change after passage of a medical
marijuana law (adjusted prevalence 16·25% pre-law vs
15·45% post-law; adjusted OR 0·92, 95% CI 0·82–1·04,
p=0·185). The interaction between grade and risk before
and after the law passed was signifi cant (p=0·001),
suggesting diff erential results by grade (table 2). Among
8th graders, marijuana use decreased signifi cantly after
passage of medical marijuana laws (table 2), but no
signifi cant change was found before versus after passage
in 10th or 12th graders (table 2). Substantial state-to-state
variability was found for pre- passage versus post-passage
risk of adolescent marijuana use (fi gure 3). States also
varied in whether the eff ects of medical marijuana laws
diff ered signifi cantly by grade.
Adjusted prevalence Adjusted odds
ratio (95% CI)
p value
Before law
passed
After law
passed
Combined grades 16·25% 15·45%0·92 (0·82–1·04)0·185
8th grade 8·14% 6·05%0·73 (0·63–0·84)<0·0001
10th grade 17·94% 18·27%1·02 (0·90–1·17)0·738
12th grade 22·68% 22·02%0·96 (0·84–1·10)0·581
Table shows marijuana use in the previous 30 days. Modal ages of students: 8th
grade 13–14 years; 10th grade 15–16 years; 12th grade 17–18 years. Adjusted
prevalences derived from the multilevel model that also includes states that did
not pass medical marijuana laws to control for historical trends. Distributions of
covariates were fi xed at grade-specifi c overall US distributions averaged over
varying numbers of years before and after the law was passed, depending on
when the change in law occurred. See appendix p 5 for absolute numbers.
Table 2: Adolescent use of marijuana before and after passage of medical
marijuana in the 21 US contiguous states that passed medical marijuana
laws up to 2014
Figure 2: Adjusted prevalence of US adolescent marijuana use* by year (1991–2014), school grade, and
whether states had medical marijuana laws
*Marijuana use refers to use in the previous 30 days. Modal ages of students: 8th grade 13–14 years; 10th grade
15–16 years; 12th grade 17–18 years. Adjusted prevalence estimates are derived from the multilevel model, fi t to all
24 years of Monitoring the Future data from the 48 contiguous US states, with individual, school, and state-
level covariates fi xed at the age-specifi c overall US distributions each year. The 21 states with medical marijuana
laws passed them in varying years, thus the yearly prevalence estimates for these states are aggregated
irrespective of whether the state had passed a law yet.
0
Year Year Year1990199520002005201020151990199520002005201020151990199520002005 201020150·05
0·10Adjusted prevalence0·15
0·20
0·25
0·30
ABCGrade 8 Grade 10 Grade 12
Average across 27 states without medical marijuana laws
Average across 21 states with medical marijuana laws
Articles
606 www.thelancet.com/psychiatry Vol 2 July 2015
Sensitivity analyses did not meaningfully aff ect results
(appendix p 3). Modelling frequency of use in the previous
30 days, the overall eff ect of medical marijuana laws on
adolescent use before versus after passage of the law
remained non-signifi cant, although (as for the overall
results), use was signifi cantly reduced in 8th but not
10th or 12th graders. Recoding the year of passage to model
delayed eff ects did not change the fi ndings for adolescents
overall, nor did our re-analyses that incorporated
dispensary information or use of marijuana in the previous
year. Finally, rerunning 48 models with interaction by
grade, removing one state at a time, results were all
signifi cant for 8th graders (adjusted OR 0·69–0·75) but
not for 10th or 12th graders (data available on request).
Discussion
In this analysis of repeated annual, cross-sectional survey
data we examined whether adolescent use of marijuana
was greater in US states that eventually passed medical
marijuana laws, and whether adolescent marijuana use
increased in these states after passage of such laws.
Compared with previous reports, we used data from a
much larger sample, and included many more states (48)
and years (24). Controlling for important covariates,
states that had ever enacted a medical marijuana law up
to 2014 had higher prevelance of adolescent marijuana
use than did other states. However, importantly, the
analyses of use pre-law versus post-law did not indicate
that adolescent marijuana use increased after passage of
NM
OR
MA
WA
VT
ME
MD
RI
IL
AZ
MN
CT
NJ
CA
MI
NY
CO
US overall
MA
AZ
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OR
MD
MN
VT
CA
NM
NV
IL
DE
CO
NY
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CT
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NH
MI
US overall
MT
WA
RI
OR
MA
MN
CO
DE
ME
NM
NH
MD
IL
CT
NJ
CA
NY
MI
AZ
US overall
MT
WA
MA
NM
OR
DE
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NV
VT
MN
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AZ
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US overall
–0·75US stateUS state–0·50 –0·25 0 0·25 –1·0 –0·5 0 0·5
–0·75 –0·50 –0·25 0 0·25 0·50 –0·5 0 0·5
A Combined grades
C 10th graders
B 8th graders
B 12th graders
Figure 3: State-specifi c risk of adolescent marijuana use before versus after passage of state medical marijuana laws
Modal ages of students: 8th grade 13–14 years; 10th grade 15–16 years; 12th grade 17–18 years. Figure shows log odds ratio (95% CI) for marijuana use in the previous
30 days. Values >0 indicate increased log odds ratios of the last month of marijuana use in the post-passage year compared with the pre-passage years; values <0 indicate
a decrease. Post-passage includes the year in which the medical marijuana law was passed. State estimates for each grade are not shown when a state did not have
pre-passage or post-passage data from the Monitoring the Future study within that grade. For 8th graders, NV did not have pre-law data and VT did not have any data
for this grade. For 10th graders, MT did not have pre-law data and RI did not have any data for this age group. For 12th graders DE, MT, and NV did not have pre-law data
and NH did not have post-law data.
Articles
www.thelancet.com/psychiatry Vol 2 July 2015 607
medical marijuana laws. To our knowledge, these
fi ndings, consistent with those from earlier studies,10,21,22
provide the strongest empirical evidence yet that medical
marijuana laws do not account for increased use of
marijuana in US adolescents.
Whether medical marijuana laws increase availability
through diversion, or change adolescent approval of
marijuana, is unknown. Irrespective of this point, our
fi ndings suggest that medical marijuana laws did not
infl uence these factors suffi ciently to raise adolescent
marijuana use. However, because adolescent norms could
aff ect risk of later adult marijuana use, and because
national trends in marijuana use might yield diff erent
results in the future, the eff ects that these laws could have
on adolescent attitudes towards the acceptability and
riskiness of marijuana use (also assessed in the Monitoring
the Future study) warrant further investigation.
Compared with states that had never passed a medical
marijuana law by 2014, adolescent marijuana use overall
was higher in states that had passed such a law, a
diff erence particularly noticeable in 12th graders. Because
this diff erence did not occur after the law was passed,
these states might diff er from the others on common
factors yet to be identifi ed (eg, norms surrounding
marijuana use25 or marijuana availability). Investigation
of these factors is warranted.
The post-law decrease in marijuana use among
8th graders was unexpected but robust across main and
sensitivity analyses (appendix p 3). One explanation for
this fi nding is that 10th and 12th graders had already
formed attitudes towards marijuana and hence were not
infl uenced by medical marijuana laws, but the younger
8th graders had more modifi able attitudes and beliefs
about marijuana, and were less likely to view marijuana
as recreational after states authorised its use for medical
purposes. Unlike 10th and 12th graders, 8th graders
show little evidence of an increase in use since 2005
(fi gure 3). Also, perhaps the passage of medical
marijuana laws and increasingly positive public attitudes
towards marijuana have focused parental vigilance and
counter-eff orts against use in the youngest adolescents.
These and other explanations should be investigated.
Until 2011, no states allowed recreational marijuana
use, but four states (Colorado, Washington, Alaska, and
Oregon) and the District of Columbia have now passed
laws permitting adult recreational use. Concerns exist
that, at least to some extent, eff orts to legalise medical
marijuana are actually concealed eff orts to eventually
legalise recreational use.30,31 Because we examined only
laws governing medical use, this report does not address
the debate about legal recreational use. Research into
the relationship between legalisation of recreational
marijuana and adolescent marijuana use is important,
but such associations cannot be inferred from the
present study.
Our study has several limitations. We did not examine
additional variations in state medical marijuana laws (eg,
the amount of marijuana permitted, or approved
illnesses), but they merit future investigation. Marijuana
use was self-reported, which is a shortcoming of large-
scale surveys. However, data were collected in confi dential
circumstances, and fi ndings from methodological studies
support the validity of this method in the Monitoring the
Future study.29 The survey did not include adolescents
who were temporarily absent from or do not attend
school; this population should also be studied. Also, some
states had only short periods after passage of medical
marijuana laws, which limited the detection of longer-
term eff ects in those states. Thus, analyses should be
repeated after more years of data have accumulated.
Finally, results might not be generalisable to states that
are considering but have not passed medical marijuana
laws. These states have lower prevalences of marijuana
use than do states with these laws, so the eff ect of medical
marijuana laws on adolescent use in these states could
diff er. Analyses should be repeated if more states pass
medical marijuana laws.
However, our study also has notable strengths. We
analysed a sample of more than 1 million adolescents
from 48 US states, with the most comprehensive time
span yet in terms of years examined. Consistency in
measures, data collection methods over time, and
consistently excellent response rates ruled out many
issues with the methods as alternative explanations of
study fi ndings, as did the sophisticated statistical
methods that we used along with controls for important
state, school, and individual covariates. In a large set of
54 sensitivity analyses, only one model suggested a
diff erent result, lending support to the robustness of our
fi ndings. Self-administered forms and data collection
procedures were designed to maximise the validity of
substance-use reporting. The validity of our report is
supported by low quantities of non-responses, high
proportions of students consistently reporting illicit
drug use, and strong construct validity. The absence of a
time trend in school participation suggests that school
non-response did not aff ect trends.
In conclusion, the results of this study showed no
evidence for an increase in adolescent marijuana use
after passage of state laws permitting use of marijuana
for medical purposes. Whether access to a substance for
medical purposes should be determined by legislation
rather than biomedical research and regulatory review
is debatable.30 However, concerns that increased
adolescent marijuana use is an unintended eff ect of
state medical marijuana laws seem unfounded. In view
of the potential for harm from early use,3–5,32–35 other
factors infl uencing wide segments of the population
need to be investigated.
Contributors
DSH, MW, KMK, MC, JS, PMO’M, SG, and RLP designed the study.
MW took particular responsibility for the statistical analysis plan, and
KMK, JS, and PMO’M for use of datasets from Monitoring the Future
study to address the research questions. DSH was responsible for
obtaining funds and prepared the fi rst and fi nal drafts of the report.
Articles
608 www.thelancet.com/psychiatry Vol 2 July 2015
15 Schwartz RH, Cooper MN, Oria M, Sheridan MJ.
Medical marijuana: a survey of teenagers and their parents.
Clin Pediatr 2003; 42: 547–51.
16 Wall MM, Poh E, Cerdá M, Keyes KM, Galea S, Hasin DS.
Adolescent marijuana use from 2002 to 2008: higher in states with
medical marijuana laws, cause still unclear. Ann Epidemiol 2011;
21: 714–16.
17 Cerdá M, Wall M, Keyes KM, Galea S, Hasin D. Medical marijuana
laws in 50 states: investigating the relationship between state
legalization of medical marijuana and marijuana use, abuse and
dependence. Drug Alcohol Depend 2012; 120: 22–27.
18 Harper S, Strumpf EC, Kaufman JS. Do medical marijuana laws
increase marijuana use? Replication study and extension.
Ann Epidemiol 2012; 22: 207–12.
19 Wall MM, Poh E, Cerdá M, Keyes KM, Galea S, Hasin DS.
Commentary on Harper S, Strumpf EC, Kaufman JS. Do medical
marijuana laws increase marijuana use? Replication study and
extension. Ann Epidemiol 2012; 22: 536–37.
20 Schuermeyer J, Salomonsen-Sautel S, Price RK, et al. Temporal
trends in marijuana attitudes, availability and use in Colorado
compared to non-medical marijuana states: 2003–11.
Drug Alcohol Depend 2014; 140: 145–55.
21 Lynne-Landsman SD, Livingston MD, Wagenaar AC. Eff ects of state
medical marijuana laws on adolescent marijuana use.
Am J Public Health 2013; 103: 1500–06.
22 Choo EK, Benz M, Zaller N, Warren O, Rising KL, McConnell KJ.
The impact of state medical marijuana legislation on adolescent
marijuana use. J Adolesc Health 2014; 55: 160–66.
23 University of Michigan. The Interuniversity Consortium for
Political and Social Research, Monitoring the Future (MTF) Series.
https://www.icpsr.umich.edu/icpsrweb/ICPSR/series/35 (accessed
June 1, 2015).
24 Johnston LD, Bachman JG, O’Malley PM, Schulenberg JE.
Monitoring the Future: a continuing study of American ICPSR
33902 youth (8th-grade and 10th-grade surveys), 2011. http://www.
icpsr.umich.edu/fi les/NAHDAP/33902-User_guide.pdf (accessed
June 1, 2015).
25 Keyes KM, Schulenberg JE, O’Malley PM, et al. The social norms of
birth cohorts and adolescent marijuana use in the United States,
1976–2007. Addiction 2011; 106: 1790–800.
26 Sevigny EL, Pacula RL, Heaton P. The eff ects of medical marijuana
laws on potency. Int J Drug Policy 2014; 25: 308–19.
27 United States Census Bureau. Metropolitan and micropolitan
statistical areas main. https://www.census.gov/population/metro/
(accessed April 15, 2014).
28 Little RJA. To model or not to model? Competing modes of
inference for fi nite population sampling. J Am Stat Assoc 2004;
99: 546–56.
29 Johnston LD, O’Malley PM, Bachman JG, Schulenberg JE.
Monitoring the Future national survey results on drug use,
1975–2010: Volume 1, secondary school students. Ann Arbor:
Institute for Social Research, The University of Michigan; 2011.
30 Kleber HD, DuPont RL. Physicians and medical marijuana.
Am J Psychiatry 2012; 169: 564–68.
31 Fischer B, Kuganesan S, Room R. Medical marijuana programs:
implications for cannabis control policy—observations from
Canada. Int J Drug Policy 2015; 26: 15–9.
32 Degenhardt L, Whiteford HA, Ferrari AJ, et al. Global burden of
disease attributable to illicit drug use and dependence: fi ndings
from the Global Burden of Disease Study, 2010. Lancet 2013;
382: 1564–74.
33 Brook JS, Adams RE, Balka EB, Johnson E. Early adolescent
marijuana use: risks for the transition to young adulthood.
Psychol Med 2002; 32: 79–91.
34 Chatterji P. Illicit drug use and educational attainment. Health Econ
2006; 15: 489–511.
35 Lynskey M, Hall W. The eff ects of adolescent cannabis use on
educational attainment: a review. Addiction 2000; 95: 1621–30.
MW did the analyses and supervised the work of TF in doing the
analyses. RLP provided defi nitions of medical marijuana laws and their
variations as determined by herself and her group of experts at RAND.
All authors contributed to subsequent versions of the report, and
approved the fi nal version.
Declaration of interests
We declare no competing interests.
Acknowledgments
The design, data collection, and management of the Monitoring the
Future study was sponsored by the National Institute on Drug Abuse
(NIDA), US National Institutes of Health, and done at the Institute for
Social Research at the University of Michigan (MI, USA; grant number
R01DA001411). The analysis, interpretation of the data, and preparation,
review, and approval of the report was funded by NIDA grant
R01DA034244. We received additional support from the National
Institute on Alcohol Abuse and Alcoholism (grant numbers
K05AA014223 for DSH and K01AA021511 for KMK); NIDA (grant
number K01DA030449 for MC), the Department of Epidemiology,
Mailman School of Public Health (SG), and the New York State
Psychiatric Institute (DH, MW).
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The press has been lapping it up like….well, water: the allegation that marijuana cultivation in
California is contributing to the state’s drought crisis. The situation has led to local governments
passing “urgency” ordinances naming the drought as an emergency, and stepping up enforcement
against medical marijuana gardens with the same claim.
Police are issuing press releases tallying up the supposed water usage for eradicated crops (which, like
their dollar amounts, seem quite inflated). A recent release from the Tulare county sheriff’s
department alleged that a 12,000-plant marijuana grow (raided by, among other agencies, the
National Guard) was slurping up 61,555 gallons of water a day.
Let’s look at the numbers:
It’s estimated by the Emerald Growers Association that, based on final yield, growing marijuana
requires an average of one gallon of water per pound, per day. With a 150-day outdoor growing cycle,
that amounts to 150 gallons per pound. Indoor growers have estimated their water use at 150-450
gallons per pound, including flushing.
With a pound weighing 454 grams, that means cannabis uses, at most, one gallon per gram, and
possibly only 1/3 that much. One joint is about a half a gram, so that the water needed to produce
one joint is somewhere between 1/6 and ½ gallon.
How does this compare to other crops, or inebriants? A glass of wine takes 15-30 gallons of water per
glass to produce; beer slightly less. A tomato requires 3.3 gallons of water, on average, while a
handful of almonds takes 5 gallons (one gallon per nut), and a 1/3-pound hamburger requires 330
gallons.
This chart compares the water consumption for single servings of different foods and beverages with
that of cannabis, in gallons:
Statewide, what is the water footprint for cannabis versus other crops? Cal NORML estimates that
in-state annual consumption for California is about 2 million pounds, or one billion grams. That figure
could be multiplied by a factor of four to account for marijuana that is diverted out of state. At the
high-end estimate of one gallon per gram, that means the cannabis crop in California, licit and illicit,
uses around 12,000 acre-feet of water yearly if grown indoors; one third of that if grown outdoors.
That compares favorably to grapes, which use 2.2 million acre-feet, rice at 2.8 million-acre feet, and
almonds, which soak up 3.7 million acre-feet of water yearly. Overall 35-45 million acre-feet of water
is used for agriculture in California, some 80% of the state's developed water supply. (Sources:
http://www.motherjones.com/environment/2014/02/wheres-californias-water-... and
http://www.nrdc.org/water/files/ca-water-supply-solutions-ag-efficiency-...)
This chart compares total water consumption by crop in California to cannabis’s consumption (in
millions of acre-feet):
The biggest users alfalfa, which requires over 5 million acre-feet of water yearly, 70% of which goes
to feed dairy cows. According to an estimate by professor Robert Glennon from Arizona College of
Law, California is exporting 100 billion gallons of water a year to China in the form of alfalfa hay.
Fracking uses an estimated 80 billion gallons of water yearly, about the same as strawberries.
Certainly, there are localized problems regarding water and cannabis cultivation in California. Cal
NORML and other groups are in favor of sound environmental regulations and licensing of
commercial-sized crops. But put into context, we can see that we can’t use the drought as an excuse
to further vilify marijuana.
Also see: Is Pot Cultivation Starving Us of Water? Keith Humphreys, July 2, 2015
Image from "The Humorous Hemp Primer," published by the German government in 1942, the same
year the US Government published Hemp for Victory.
August 3, 2015 - California NORML has written to Scott Bauer of California Fish and Wildlife
questioning his often-repeated estimation that marijuana plants use 5-10 gallons of water every day
throughout their growing season (June-October). This figure has been extrapolated to cause law
enforcement to overestimate the water consumption of gardens they raid, much as they have always
overestimated plant yields and prices.
Public officials such as Sacramento County supervisor Roberta MacGlashen have cited the figure as a
reason to double fines on marijuana patients, meaning growing even a single outdoor plant in the
county can be cause for a fine of up to $1000/day. The Sacramento Bee has editorialized against using
water on any outdoor cannabis plants.
From what Cal NORML has been able to uncover, Fish and Wildlife did not measure or
calculate their water usage estimate, but rather lifted data from a 2010 paper from the Humboldt
Growers Association and other sources, such as a paper from Chris Van Hook of Clean Green
Certification that was written in 2013 to encourage cannabis farmers to store water.
Articles co-authored by Bauer in Bioscience and PLOS both cite a 2010 Humboldt Growers Association
calculation of six gallons/plant each day, based on commonly used irrigation methods (towards the
end of the document).
But while HGA farmers tend to grow extremely large plants, those eradicated in the wild generally
receive far less attention, meaning they are much smaller and therefore require only a fraction of the
water used on plants that look more like trees (see photos).
The authors averaged an estimate by Mendocino Sheriff Tom Allman that large marijuana plants
require one gallon of water per day and Van Hook's statement that in extremely hot weather, large
plants can use up to 15 gallons per day to bolster their figure.
In an email communication, Van Hook told Cal NORML that at the time he collected data (in 2010) for
his 2013 paper, "water was not an issue. I have seen some real improvements since then which is a
testament to California agriculture. Just like any agriculture when a problem arises responsible
farmers work to improve. I would like to see a new study with some of the water saving
improvements I have seen out in the field.”
Bauer and his co-authors state:
Water use data for marijuana cultivation are virtually nonexistent in the published literature, and both
published and unpublished sources for this information vary greatly, from as low as 3.8 liters up to
56.8 liters per plant per day.
This is quite a wide range. They continue:
The 22.7 liter (6 gallon) figure falls near the middle of this range, and was based on the soaker hose
and emitter line watering methods used almost exclusively by the MCSs we have observed.
However, how long or often the crops were watered cannot be known from this information. They
continue:
Because these water demand estimates were used to evaluate impacts of surface water diversion from
streams, we also excluded plants and greenhouses in areas served by municipal water districts.
Which is exactly what the Sacramento Board of Supervisors oversees. Legal experts say it’s
questionable whether or not growers charged criminally can also be subjected to fines under local
ordinances, so it’s likely that Sacramento’s ordinance will affect only backyard growers.
COMING UP WITH BETTER DATA
So far, Sacramento NORML and Cal NORML have canvassed growers from 11 outdoor farms in El
Dorado, Placer, Humboldt and Mendocino counties. Water usage has ranged from 1 gallon/plant to 3.5
gallons, although plants were not necessarily watered daily, and less water was used while the plants
were still immature. Growers also often scale back on watering at the end of the season, to encourage
flowering. Six gallons a day is possible for July and August, but not for 150 days, said one farmer from
Mendocino county. The average number of gallons used on plants daily was 2.30 in NORML’s
study.
The more pertinent way to look at the issue is in gallons of water per gram of marijuana
bud produced. A representative from the Mendocino Cannabis Policy Council said his members tend
to grow 2-4 pound plants, with the yield directly related to the amount of water used. Roughly, MCPC
and Emerald Growers Association estimate that an average of 1 pound (454 grams) is yielded using
an average of one gallon per growing day. So a two-pound plant would require an average of two
gallons per growing day, and a four-pound plant would use four gallons.
Using the gallon/day/pound ratio means one gallon yields about two grams of processed bud at a
growing season of 240 days (a figure which can be reduced down to 90 days with the use of
light-depravation techniques). Two growers in Humboldt county said that they reliably grow
two-pound plants watering with 2.5 gallons/day (but not necessarily every day). Taken in total, both
estimated that it took an average 2/3 of a gallon daily to yield one pound of bud, one saying he
multiplied that by 100 growing days. A farmer in Mendocino who uses water conservation techniques
estimates using only 0.3 daily gallons per pound of bud. Adding in two farms in the Sacramento area,
one that got 1.22 grams/gallon (using Smart Pots that may have lead to evaporation) and a second
that yielded 0.87 grams/gallon, Cal NORML calculates an average of 0.72 gallons of water is
needed to produce a gram of marijuana, no matter how many plants are grown or how big
they are.
Since a “joint” of marijuana is about 1/2 of a gram, this means a dose of medical marijuana requires
less than half a gallon of water. A hamburger requires over 100 gallons of water to produce, and a
serving of rice takes around 50 gallons. (Source: UNESCO via LA Times).
TURNING WATER INTO WINE VS. WEED
We have also investigated the often-repeated statement that marijuana uses twice as much water as
do wine grapes, from the Bioscience article.
Using the author’s figure of 22 L (6 gallons) of water per plant per day from June - October, they
state:
...if we assume a planting density of 130,000 plants per km2, water application rates would be
approximately 430 million L per km2 of outdoor-grown marijuana per growing season. For
comparison, wine grapes on the California north coast are estimated to use a mean of 271 million L of
water per km2 of vines per growing season. Marijuana is therefore estimated to be almost two times
more “thirsty” than wine grapes, the other major irrigated crop in the region.
But let’s look at the output from those acres planted, and the total acreage.
Estimates say that about 150-160 gallons of wine are produced per ton of grapes. The amount of
grapes grown per acre of land can vary from 2-30 tons, with 4 tons seeming to be the most commonly
used figure. Using 8 tons of grapes per acre, we calculate that 26 gallons of water are required to
produce a 4-ounce glass of wine. This comes close to the 26-29 gallons/serving of wine from UNESCO
data. (For some reason the LA Times, citing UNESCO, says it takes 3.48 gallons of water to produce
an ounce of wine, which is why we had previously reported it took about 15 gallons of water per glass;
calculating directly from UNESCO the figure is 7 gallons per ounce and 28 gallons per glass.)
By contrast, we estimate that between 1-1.5 tons of marijuana are produced per acre. Using Fish &
Wildlife’s figure of 430 million L per km2, this means between 0.63-0.95 gallons of water are
used per 1/2 gram serving of marijuana, or 27-41 times less than the water it takes to
produce a glass of wine.
Now let’s look total acreage. In 2014, the USDA reports that the total acreage of wine grapes grown in
California was 615,000. Our estimates for total acreage of marijuana required for California
consumption is 800 acres (with no space between plants); 3000 acres would be a ballpark figure. That
ups the differential by a factor of 200, meaning overall wine production uses 5000-8000 times
more water than does marijuana in California.
Wine production has been extremely damaging to rivers and creeks in critical salmon-spawning
streams. For the past several years, Emerald Growers and other groups have been educating farmers
about fish-friendly growing practices and the Small Farmers Association drought management plan
calls for goals of 1/2 gallon to 1 gallon per plant for daily use.
CULTIVATION BANS IMPEDE WATER REGULATORS
Certainly, Cal NORML is concerned about severe, localized problems regarding large marijuana farms
and water use. Bauer's articles are about local problems that the press has wildly extrapolated on.
PLOS study co-author Lori Pottinger said in answer to an email from Cal NORML "I hope we conveyed
that this was a localized problem, that was certainly the intent."
Taking a statewide view, even using Bauer’s figures marijuana uses a tiny portion of the water used
yearly in the state on almonds (3.7 million acre-feet); grapes (2.8 million acre-feet) and rice (2.2
million acre-feet). Commercial agriculture in California uses an estimated 25-45 million acre-feet of
water. By comparison, the cannabis industry is estimated to use a mere 3000-15,000 acre feet of
water per year. That means cannabis cultivation uses 0.04 percent or less of all the water
used for agriculture in California.
In fact, at a recent hearing in the Capitol on the drought, all the fisheries experts spoke about the
problems in the Delta (e.g. Shasta Dam and the Thermolito) but all the law enforcement panelists
focused on the Emerald Triangle. Big Ag, in the form of rice farmer and Congressman Doug LaMalfa
and his successor Sen. Jim Nielsen, and billionaire pomegranate and pistachio farmer Stuart Resnick
via his contributee Sen. Dianne Feinstein, have been instrumental in keeping water flowing to farms.
Coincidentally(?) LaMalfa, Nielsen and Feinstein are all against marijuana legalization.
Ironically, counties like Sacramento, Butte, Shasta, Tehama and Fresno that have cultivation bans will
be unable to sign up farmers for the Central Valley Water Board’s pilot program regulating water use
and discharge, due to be finalized in October.
Cal NORML has long worked for regulation of commercial marijuana gardens at a state level, and is
participating in discussions about AB 266 and AB 243, which would finally provide oversight on the
state’s 19-year-old medical marijuana law.
Marijuana Odor Perception: Studies Modeled
From Probable Cause Cases
Richard L. Doty,1,3 Thomas Wudarski,1 David A. Marshall,1,2
and Lloyd Hastings1
The 4th Amendment of the United States Constitution protects American citizens against
unreasonable search and seizure without probable cause. Although law enforcement
officials routinely rely solely on the sense of smell to justify probable cause when entering
vehicles and dwellings to search for illicit drugs, the accuracy of their perception in this
regard has rarely been questioned and, to our knowledge, never tested. In this paper, we
present data from two empirical studies based upon actual legal cases in which the odor of
marijuana was used as probable cause for search. In the first, we simulated a situation in
which, during a routine traffic stop, the odor of packaged marijuana located in the trunk of
an automobile was said to be detected through the driver’s window. In the second, we
investigated a report that marijuana odor was discernable from a considerable distance
from the chimney effluence of diesel exhaust emanating from an illicit California grow
room. Our findings suggest that the odor of marijuana was not reliably discernable by
persons with an excellent sense of smell in either case. These studies are the first to
examine the ability of humans to detect marijuana in simulated real-life situations
encountered by law enforcement officials, and are particularly relevant to the issue of
probable cause.
KEY WORDS: marijuana; psychophysics; law; olfaction; magnitude estimation.
The 4th Amendment of the United States Constitution protects American citizens against
unreasonable search and seizure without probable cause. Probable cause for search
occurs when known facts and circumstances of a reasonably trustworthy nature are
sufficient to justify a person of reasonable caution and prudence in the belief that a
crime has been or is being committed (Draper v. United States, 1959). Although this
definition is common to most legal textbooks, the subjective nature of this justification
can be problematic in practical application. This issue becomes
1Smell and Taste Center, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania. 2Dr. David A.
Marshall is deceased.
3To whom correspondence should be addressed to Smell and Taste Center, University of Pennsylvania Medical
Center, 5 Ravdin Building, 3400 Spruce Street, Philadelphia, Pennsylvania 19104; e-mail: doty@
mail.med.upenn.edu.
Law and Human Behavior, Vol. 28, No. 2, April 2004 ( C° 2004)
223
0147-7307/04/0400-0223/1 C° 2004 American Psychology-Law Society/Division 41 of the American Psychology Association
particularly troubling when the sensory perception of weak stimuli, such as faint odors,
is the basis for search.
Law enforcement officers often justify searches with their sense of smell when
other more tangible criteria are not present. This type of encounter often occurs when
the odor of marijuana (Cannabis sativa L.) is the basis for probable cause for entering
vehicles and dwellings to search for illicit drugs (e.g., United States of America v. Boger,
1990; United States of America v. Ellis, 1998; United States of America v. Reilly, 1994; United
States of America v. Shates, 1995). Unfortunately, little research exists on the human
capacity to detect marijuana’s odor in either laboratory or specific real-life situations,
despite its widespread acceptance by law enforcement. This dearth of information bears
considerable legal consequence, because courts often accept the argument, prima facie,
that marijuana’s odor can always be detected. In one instance, for example, police officers
reported the smell of marijuana when a subsequent search revealed only cocaine (United
States of America v. Harris, 1994). This case exemplifies the misappropriate use of smell
for probable cause, and clearly illustrates a grave problem that must be addressed.
It is generally believed that the characteristic marijuana odor can be discerned from
a wide variety of C. sativa plants, regardless of their geographic origin, strain, extent of
processing, and tetrahydrocannabinol (THC) content. However, such beliefs are based largely
on anecdote, and there is a disturbing absence of quantitative information on this topic.
One study reports that all volatile oils prepared from freshly collected C. Sativa buds have a
characteristic marijuana smell (Ross & El Sohly, 1996), although no formal organoleptic
investigation was made. It is not clear whether subtle differences exist in the smell of these
oils, but it has been suggested that the essential oil of C. sativa may differ enough
among geographic locations to serve as a chemical marker for general origin or type
(Hemphill, Turner, & Mahlberg, 1980). However, the considerable variability in the
chemical composition of such volatiles among plants even from the same location may
make such discernment extremely difficult, if not impossible (Hood & Barry, 1978).
The present studies arose from the need to better understand the nature of marijuana’s
odor and whether humans can discern this odor in situations modeled from “real-life” law
enforcement encounters. The first set of experiments investigated a situation in which
the arresting officer reportedly discerned processed marijuana within an automobile
trunk from the passenger compartment. In this work, we initially determined whether
marijuana odor was discernible through the walls of the plastic bag containing the
marijuana. Following confirmation of this point, we determined whether this discernment
could occur inside the passenger’s compartment of a car when the trunk contained the same
packaged marijuana.
The second set of experiments was based upon a situation present in an illicit
marijuana grow house in northern California. In the grow house, odors from immature
Cannabis sativa plants were combined with diesel exhaust from a generator and expelled out
through a chimney. Law enforcement officials reported being able to smell the marijuana
from a road several hundred yards away, and subsequently used this odor as probable cause
for a search. In this second set of studies, we first sought to determine whether the odor of
immature marijuana plants differs in quality or intensity from that of mature marijuana
plants. We then investigated whether participants
224 Doty, Wudarski, Marshall, and Hastings
were able to smell marijuana odor from a mixture emanating from immature C. sativa
plants when combined with diesel engine exhaust. The ratio of marijuana odor to exhaust
was modeled from the chimney effluence of the illicit California grow room.
EXPERIMENT 1
Study 1
The purpose of this study was to determine whether a group of men and women could
distinguish the odor of packaged marijuana from that of a matched blank odor source.
Methods
Participants. Five men and four women recruited from advertisements placed on
community bulletin boards served as participants. None reported being a smoker of
marijuana, and all were nonusers of tobacco products. Most were in their “20s”
(median = 27 years) and all reported being in good general health. All were
medication-free, and scored within normal limits on the University of Pennsylvania Smell
Identification Test (UPSIT), a standardized olfactory test (Doty, 1995; Doty, Shaman,
& Dann, 1984).
Test Procedures. Prior to formal testing, the participants familiarized themselves
with the odor of a sample of processed Mexican marijuana supplied by the New Jersey
Attorney General’s Office. A State law enforcement official was present during the testing
and was custodian of the marijuana. Formal testing was performed in a 14 £ 17 ft2 room
with excellent air circulation. Each participant was blindfolded and led in one at a time at
approximately 5-min intervals, at which point they were asked to sniff two garbage
bags in succession (“Hefty” brand, 2-ply, 1.5 mil). One contained five 1-pound
packets of pressed and processed Mexican marijuana and the other newspapers
crushed and bundled in a similar fashion. Each participant was then required to report
the bag that smelled most like marijuana. Half of the participants received the
marijuana-containing bag first, so as to counterbalance test order.
Results
All nine participants reliably and unequivocally reported the garbage bag containing
marijuana to have a marijuana-like smell, and none reported the control garbage bag as
having such an odor (Binomial test, p < .002).
Study 2
The purpose of this study was to assess whether participants can reliably smell, from the
driver’s compartment of an automobile, the odor of the marijuanacontaining garbage
bag housed in the trunk.
Marijuana Odor Perception 225
Methods
Participants. The nine participants described in Experiment 1, who were now
experienced in recognizing the odor of marijuana, participated in this study.
Test Procedures. This experiment was designed to simulate the conditions present
when a 1983 2-door Chevrolet was searched for the presence of marijuana. Thus, the
same automobile was provided by the State of New Jersey for this study, and the
temperature at testing was only 0.6±C different than on the day of the arrest. In the real-
life situation, the estimated time that the marijuana had remained in the closed trunk prior
to driving away from the procurement site was 20 min, followed by 10 min within the
trunk with the heater on and the windows shut.
In this study, four test sessions were conducted with either the marijuana or blank
bag in the trunk compartment of the automobile. The bag was placed in the trunk for 20
min, and then the automobile was driven for 10 min. The automobile was then parked in
the street where an experimenter monitored the participants and recorded their responses.
This study was conducted double blind with neither the tester nor the participant knowing
what was in the trunk. A technician was aware of which bag was placed in the trunk during
each of the trials, and did not communicate this to anyone else involved until after the study.
During each of the four test sessions, the nine panel members were led individually
at 2-min intervals to the driver’s side of the automobile. The following instructions were
then read to the participant: “When the driver gets out, sniff in the front seat area, and in
the back seat area, and tell me if you smell the odor of marijuana. Tell me your response,
yes or no, after you have finished sampling and the driver has gotten back into the car and
closed the door.” This process was repeated three times within each test session, providing
a total of 27 trials per session. The participants were sequestered out of view of the
automobile between trials, so they had no knowledge as to whether the odorant stimulus
was changed or remained the same during the test session. After each session was completed,
the stimulus bag was removed from the trunk and the trunk lid remained open for 5 min to
permit airing out before the subsequent session.
Results
Six of the nine participants reported no marijuana odor being present on any of the
six marijuana trials or any of the six nonmarijuana trials (Table 1). In aggregate the
number of false positives (9.26%; 5 of 54 trials) was essentially the same as the number of
correct positives (12.96%; 7 of 54 trials). A one-tailed Fisher exact probability test revealed no
meaningful difference between the hit and false positive rates (p > .20).
EXPERIMENT 2
Experiment 2 was conducted in a state sanctioned medical Cannabis growing
facility in Northern California. We first addressed whether nonbudding and budding
226 Doty, Wudarski, Marshall, and Hastings
Table 1. Hit and False Positive Rates for Identifying the
Odor of Marijuana in Experiment 1, Study 2
Participant Gender Hit rate False alarm rate
1 Male 0 of 6 0 of 6
2 Male 0 of 6 0 of 6
3 Male 0 of 6 0 of 6
4 Female 0 of 6 0 of 6
5 Female 0 of 6 0 of 6
6 Female 0 of 6 0 of 6
7 Male 2 of 6 3 of 6
8 Male 1 of 6 0 of 6
9 Female 4 of 6 2 of 6
Totals 7 of 54 5 of 54
marijuana plants produce similar odors. We then investigated if low levels of diesel
exhaust fumes could mask the odor of immature marijuana plants.
Study 1
Methods
Participants. Five men and one woman, ranging in age from 20 to 57 (M = 41.5
years, SD = 14.3), served as participants. These individuals were recruited by word of
mouth from the neighborhood surrounding the California grow facility, and all
reported being in good general health. All exhibited above average smell function, as
measured by the UPSIT (Doty, 1995; Doty, Shaman, & Dann, 1984)
Stimuli and Test Procedures. The test stimuli consisted of four immature (nonbudding)
female Cannabis plants, one mature (budding) female Cannabis plant, one female
tomato plant (Lycopersicon), and one empty container containing planting soil. Only
one mature Cannabis plant was used because the odor from this Cannabis plant was
distinctive. Female plants were used because they produce more flower biomass than
male plants, and are preferred by marijuana growers. Cannabinoids, such as 19-
tetrahydrocannabinal, tend to be particularly concentrated in the flowerrelated bracts (Turner,
Hemphill, & Mahlberg, 1980).
Polyethylene bags with no discernable odor were placed over each of the plants or the
planting pot containing soil. The bags were positioned to collect the vapors emanating
from the plant and associated potting soil. These vapors were sniffed by participants
through a 20-cm long, 2.54-cm odorless PVC tube inserted through a slit in the bags.
The temperature of the room in which testing occurred was
»21±C.
Although all six participants indicated that they were aware of the smell of marijuana, we
provided a sample to ensure familiarization with the odor. The participants were not
informed of the positioning of the stimulus pots on the sampling table, and wore opaque
goggles to preclude visual input.
Each participant was guided to the stimulus plant by an experimenter, who
inserted the tube into the plant environs. The experimenter then positioned the participant’s
hands on the tube so as to enabling them to sniff through its end. The order of smelling the
stimuli was systematically counterbalanced both between participants
Marijuana Odor Perception 227
and within trial sessions of the same participant to preclude confounding by order
effects. At least 45 s was interspersed between trials to minimize possible adaptation
effects. The sniffing tubes were also cleaned with ethanol and water after use to eliminate any
residual odors that accumulated during the test session.
The task of the participants was to report not only whether or not marijuana odor
was present, but to quantitatively compare the relative intensity of the total odor using a
magnitude estimation procedure. In this procedure odors are related relative to one another
without a standardized scale (termed the free-modulus method). Because magnitude
estimation numbers are ratio in nature, an assignment by a given participant of 25 to a
stimulus theoretically is perceived half as intense as an assignment of 50. This method is well
documented in the psychophysical and organoleptic sensory literature (Doty, 1975; Marks, 1988;
Moskowitz, Dravnieks, Cain, & Turk, 1974). The judgments were collected on three separate
occasions, resulting in a total of 126 trials within the whole study. The median of the three
intensity judgments for each participant was used as the intensity test measure.
Results
The identification data of the six participants revealed that: (i) the mature Cannabis
plant was always rated as having a characteristic marijuana odor; (ii) three of the four
immature Cannabis plants never were found to have a distinctive marijuana odor; (iii)
one of the four immature Cannabis plants was always rated as having a marijuana-like
smell; and (iv) the potting soil alone was always reported as having an odor, but never as
having a marijuana-like odor.
The median magnitude estimates of the odor intensity for the potting soil, immature
marijuana, mature marijuana, and tomato plant stimuli were calculated, and because
magnitude estimation numbers are arguably ratio in nature, we determined ratios of the rated
intensities relative to the baseline estimates of potting soil. These ratios are presented in Table
2.
Table 2. Magnitude Intensity Estimates Adjusted in Relation
to the Intensity Estimates of Potting Soil for Participants in
Study 1 of Experiment 2
Median odor intensity estimates in relation
to those of potting soil
Participant
Immature
Cannabis
Mature
Cannabis
Immature
Lycopersicon
(Tomato plant)
1 1.28 57.14 0.57
2 2.00 10.00 2.00
3 1.00 2.00 1.00
4 0.97 1.11 0.69
5 0.83 3.33 1.33
6 2.00 5.00 1.50
Note. For example, the first participant found the odor of immature
marijuana to be 1.28 times more intense than the odor of potting soil
alone, whereas the second found this odor to be two times more intense
than that of the potting soil.
228 Doty, Wudarski, Marshall, and Hastings
It is clear from Table 2 that all six participants found the volatiles emanating from
the mature marijuana plant to be more intense than the volatiles emanating from the
immature marijuana plants or from the tomato plant. Statistical analysis using the
nonparametric Wilcoxin matched-pairs signed ranks test revealed that volatiles
emanating from the mature Cannabis plant were judged as having a significantly
stronger odor than both the volatiles from the immature Cannabis plant and the tomato
plant (p < .025). Additionally, the intensities of the immature Cannabis plants did not differ
significantly from the tomato plant.
Study 2
The purpose of Experiment 2 was to determine whether diesel exhaust odor could
mask the odor of volatiles from Cannabis sativa L under a specific set of “realworld”
circumstances. We aimed to conservatively model, within reasonable bounds, a situation
present in the aforementioned California grow room where the exhaust of volatiles from
immature Cannabis sativa plants were combined with diesel exhaust from a generator
and expelled outside through a chimney. In effect, we sought to determine whether
the odor of marijuana volatiles could be discerned from the background of diesel exhaust
odor under conditions similar, or even more stringent, to those in this specific situation.
Methods
Participants. Five of the 10 participants in this experiment were the male par-
ticipants of Study 1. One new participant was a female, and the other four new
participants were male. The UPSIT was administered to three of these additional
individuals and all were within normal limits. The remaining participants reported no
problems smelling, although their sense of smell was not formally evaluated. Three of
the five new participants reported having intimate knowledge of the smell of
marijuana and admitted to being occasional or regular marijuana smokers.
Procedures. We employed an olfactometer capable of providing, for nasal sam-
pling, a mixture of diesel exhaust and Cannabis volatiles in the relative proportions
estimated to have been present within the chimney effluence of the illicit marijuana grow
room (see Fig. 1). In this system, clean room air was pumped into two identical 114-l
galvanized steel chambers at a rate of 68 l/min. In one of the 114-l chambers, two
marijuana plants (»38 cm high) were situated; the other housed identical containers
and potting soil, but no plants. To produce and maintain a temperature in these
chambers equivalent to that present in the illicit grow room (approximately 27±C),
digital temperature probes and 150-watt light bulbs were placed within them. The chamber
temperatures were continuously monitored and the intensity of the light bulbs
adjusted via a rheostat to maintain the temperatures at the desired level
(range: 25±–28±C).
It should be noted that the two Cannabis plants employed in this study were
selected from a larger number of similar plants available to us at the growing facility. We did
not wish to bias the selection procedure, so none of these plants had been
Marijuana Odor Perception 229
Fig. 1. Schematic diagram of olfactometer that allowed for mixing of diesel odor and
marijuana volatiles for sampling by participants. signifies ball valves.
previously smelled. Each was assigned a number, and the two numbers chosen were
determined using a random process.
The output of the olfactometer was channeled through a PVC pipe to a sampling
port from which the participants made their observations. During the intertrial intervals, the
test mixture was directed from the sniffing port. The basic parameters that had to be met or
exceeded in the simulation were derived from measurements of the illicit California grow
room and were as follows: (i): the volume of the air in the grow room (190.5 m3); (ii) the
number of immature plants reportedly housed in the grow room (440); (iii) the air flow
through the grow room (calculated at 65.14 l/min); and (iv) the empirically determined flow
rate of diesel engine exhaust (3.8 m3 per minute at 19±C). The degree of dispersion of
chimney effluent into the ambient air, which would dilute the effluent considerably and
make detection even more difficult, was not included in the model.
In the original situation, one plant occupied 0.43 m3. However, the plants in the original
illicit grow room were somewhat larger than those available to us for study. Therefore, because
one plant originally occupied 0.43 m3, we placed two plants in the galvanized steel container
(114 l). This provided a cushion of error to compensate for differences in plant density and
any minor errors that may be present elsewhere in the model (e.g., differences between
actual and measured flow rates). Additionally, a higher ratio of marijuana (or potting soil
chamber) air to diesel exhaust effluent was employed to make even more conservative the
test as to whether marijuana odor could be discerned within diesel exhaust.
The psychophysical paradigm consisted of 20 test trials given to 17 of the test
participants. The number of trials of three participants was abbreviated because of
schedule conflicts, resulting in 19 trials in two cases and 15 trials in the remaining case.
In sum, 193 total trials were completed in the experiment. On half of the trials the diesel
exhaust was presented with no marijuana odor (i.e., just the odor of potting
230 Doty, Wudarski, Marshall, and Hastings
soil), and on the other half the diesel exhaust was presented with the volatiles emitted
from the marijuana plants and their potting soil. After switching the valves to a new test
condition, 3–5 min were allowed to pass before testing commenced to insure adequate
purging of the odors from the previous test condition.
The entire test session lasted approximately 3 hr. Each participant was tested
individually and was instructed not to discuss his or her responses with the other
participants. No information regarding the probability of a marijuana trial relative to a
blank trial was provided. All participants received testing on a specific trial before the
olfactometer was reset for the next trial. The task of each participant on each trial was
to answer two basic questions: (i) do you smell diesel exhaust?; and (ii) do you smell
marijuana odor?
Results
No convincing evidence was present in the data that any of the participants could
reliably detect the marijuana odor embedded in the diesel fumes. A onesided Fisher
exact probability test revealed no meaningful difference between the hit (6 of 96
trials) and false positive (3 of 96 trials) rates, implying that this level of responding to
the diesel + marijuana vapor stimulus is within a range expected by chance. Hence,
the data provided no statistical support for the notion that human participants can
discern marijuana odor from diesel odor under the conditions of this experiment.
GENERAL DISCUSSION
In Experiment 1, we demonstrated that the odor arising from 2.5 kg of processed
Mexican C. sativa is clearly discernable through a tightly sealed garbage bag sniffed at point-
blank range. However, when the marijuana-containing garbage bag was placed in the
trunk of an automobile under conditions analogous to those present in an actual search and
seizure operation, there was no convincing evidence that the marijuana odor could be
discerned.
In Experiment 2, we demonstrated that odors emanating from immature female
marijuana plants are much less intense on average than odorous volatiles emanating from
mature female marijuana plants. We also discovered no marijuana-like odor could be
discerned in most immature marijuana plants. Consequently, participants were also
unable to discern the odor of immature marijuana plants when they are mixed with
diesel exhaust fumes in a ratio modeled from a real-life growing situation in an illicit
California grow room. This failure to accurately discern marijuana was nearly
absolute, with low false alarm and false positive rates. This presumably reflects, on the
part of participants familiar with this odor, the expectation of a distinct marijuana smell that
rarely, if ever, presented itself. A more liberal criterion, that is, a tendency to make
both higher hit and false alarm rates, would be expected in persons who would have
greater benefit in detecting the presence of marijuana, as might occur in some law
enforcement situations.
These studies represent the first step in better understanding the nature of marijuana’s
odor and situations in which it can be perceived. However, these experiments
Marijuana Odor Perception 231
are potentially limited to the rather specific conditions under which they were per-
formed, and by the relatively small number of participants tested. Thus, their findings need
not necessarily generalize to other, even seemingly similar, situations. For example,
temperature is known to influence the release and diffusion of molecules from plant
products. The inability to detect marijuana located in the trunk of a car from the driver’s
window may be different in on a hot summer day than under the winter conditions present
in Experiment 1.
The participants of Experiment 1 had limited experience with marijuana odor, unlike the
participants of Experiment 2. The degree to which use, or long-term experience with,
marijuana-containing products on the ability of participants to recognize marijuana odor is
unknown. In general, participants who are formally trained to recognize tastes and odors
perform better on psychophysical tests, suggesting that training can alter some indices of
performance (Smith, Doty, Burlingame, & McKeown, 1993). The contention that law
enforcement officers may be more accurate than laypersons in detecting marijuana by
odor, however, requires substantiation. Other factors, including gender and age, may have
a much more salient influence on the ability to smell and to detect marijuana at low
concentrations (Doty et al., 1984). Just as with canines, standardized procedures are needed
to establish the smell ability of law enforcement officers who are called on to testify about
odors of elicit drugs.
Importantly, one must not overlook the fact that expectation or suggestion can often
dictate the likelihood of a person believing that they smell an odor, a common problem in
environmental annoyance issues. In the field of olfactory psychophysics, some participants
report detecting odors even on blank trials (van Langenhove & Schamp, 1989). This
phenomenon is illustrated by a demonstration described by William James, the eminent
nineteenth Century psychologist (James, 1890). Professor James told a classroom of
students that he was about to open a small bottle with a very strong odor in it, and that
they were to raise their hands when they first noticed the smell. A few minutes after
removing the bottle top, students in the first rows of the lecture hall began raising their hands,
and in a matter of minutes the whole room was filled with raised hands. In fact, the bottle
had no discernible smell, containing only the vapors of water and a dying agent used to the
make the water look dark!
The present findings throw into question, in two specific instances, the validity of
observations made by law enforcement officers using the sense of smell to discern the
presence of marijuana. Although these instances reflect a very small set of studies with
very specific constraints, they do suggest that a blanket acceptance of testimony based
upon reported detection of odors for probable cause is questionable and that empirical data to
support or refute such testimony in specific cases is sorely needed.
ACKNOWLEDGMENTS
This work was supported, in part, by funds from the Attorney General’s Office of
the State of New Jersey and from the United States District Court, Northern District of
California, San Francisco, California.
232 Doty, Wudarski, Marshall, and Hastings
Marijuana Odor Perception 233
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Marijuana Equivalency
in Portion and Dosage
August 10, 2015
Prepared for the Colorado Department of Revenue
An assessment of physical and pharmacokinetic relationships
in marijuana production and consumption in Colorado
The authors are grateful for suggestions
and assistance from Lewis Koski, Ron
Kammerzell, Jim Burack, Dr. Franjo
Grotenhermen, M.D., Dr. Kari Franson,
M.D., and all the businesses that hosted
the team and contributed information
to this study. Any omissions or errors
are the sole responsibility of the report
team.
This report was commissioned under
Colorado HB 14-1361. The Colorado
Department of Revenue retained the
University of Colorado, Leeds School of
Business, Business Research Division,
in partnership with the Marijuana
Policy Group, and BBC Research &
Consulting, to produce an unbiased
and scientifi c report for the purpose of
rulemaking by Colorado stakeholders.
Version 12 / August 10, 2015
Corresponding author:
Adam Orens
aorens@mjpolicygroup.com
Authors
Adam Orens
Miles Light
Jacob Rowberry
Jeremy Matsen
Brian Lewandowski
MPG
Marijuana Policy Group
Marijuana Equivalency
in Portion and Dosage
An assessment of physical and pharmacokinetic relationships
in marijuana production and consumption in Colorado
4 Equivalency Report
Table of Contents
EXECUTIVE SUMMARY 6
Physical Equivalency 6
Pharmacokinetic Equivalency 7
Market Price Equivalency 8
OVERVIEW AND MOTIVATION 11
Production, Price, and Dosing Equivalencies 11
Use of Metrc™ Data 12
PREVAILING MIP PRODUCTION TECHNIQUES 13
THC vs. THCa 13
Production Technique Summary 13
Hydrocarbon Extraction Process 14
Carbon Dioxide Extraction Process 15
Butter and Cooking Oils 15
Other Solvents 16
PHYSICAL EQUIVALENCY CALCULATIONS 17
Alternate Methodology 21
PHARMACOLOGICAL EQUIVALENCIES 23
Enumeration of THC Uptake Methods for Marijuana 23
THC, THCa, 11-OH-THC and THC-COOH 24
Identifi cation of THC Uptake and Benchmarking 24
Role of the Blood-Brain-Barrier (BBB) 27
Constructing Dosing Equivalencies for Marijuana Products 28
Identifi cation of Parameter Values 30
A Worked Example 33
Resulting Equivalency Tables 34
Oils, Tinctures, Lotions, and Less Common Uptake Methods 35
MARKET PRICE COMPARISON 36
REFERENCES 41
TERMS & ACRONYMS 44
6 Equivalency ReportEXECUTIVE SUMMARYgrown in Colorado and may not share similarities with
product in other regions. Overall, the study is designed
to meet the requirements of Colorado House Bill 14-1361
and focuses solely on the retail adult-use marijuana
market in Colorado.
PHYSICAL EQUIVALENCY
Physical equivalencies were calculated in two ways – a
THC equivalency, and a physical production equivalency.
Physical equivalencies were calculated for the major
concentrate and infused product manufacturing tech-
niques, including butane hash oil, CO2 oil, ethanol, and
water. Physical production equivalency is calculated by
isolating the marijuana trim and shake inputs and deter-
mining a yield ratio. The THC methodology provides an
equivalent amount of THC in various forms of marijuana
products based on recent state testing information Table
ES-1 shows equivalency factors for both methodologies
by solvent type.
The physical equivalencies in Table ES-1 show that
between 347 and 413 edibles of 10mg strength can be
produced from an ounce of marijuana, depending on the
solvent type and production method. For concentrates,
between 3.10 and 5.50 grams of concentrate are equiv-
alent to an ounce of fl ower marijuana.
The THC equivalency factors in Table ES-1 can be inter-
preted as showing units with equivalent amounts of THC
based on recent state testing data. For instance, given
the uniform dosage amounts of edibles in Colorado,434
edibles of 10mg strength and one ounce of fl ower mari-
juana at average potency have an equivalent amounts
of THC. For concentrates, between 6.91 and 8.50 grams
of concentrate (depending on solvent) and an ounce of
fl ower marijuana at average potency have an equivalent
amount of THC.
The original legislation to legalize and regulate marijuana
in Colorado does not explicitly restrict marijuana concen-
trates and infused edibles. Over time, these marijuana
products have become more popular, prompting new
legislation to remedy the omission. House Bill 14-1361
now stipulates limits upon marijuana fl ower portions, “or
their equivalent.”
This study provides scientifi c and data driven evidence
in order to understand these equivalencies. The results
provide comparisons between marijuana fl ower, concen-
trates and infused products specifi cally for Colorado’s
marijuana market.
Equivalency can be viewed from three perspec-
tives: production, dosing, and market price. The fi rst
perspective relates to physical production, where infused
edibles or concentrates are traced back into their corre-
sponding weight of fl ower or trim inputs. This enables
the conversion from non-fl ower products into a common
fl ower-based denominator, so that aggregate use can be
measured across different marijuana product types.
The second perspective uses pharmacology to develop
a dose-equivalent measure across product types. The
results equate the dosing effects between inhaled and
ingested marijuana products. Finally, the third perspective
uses Colorado potency and market data to convert mari-
juana retail prices into their unit-THC equivalents. These
THC-based prices are then compared across product
types. A powerful and reassuring fi nding is that Colo-
rado’s market prices refl ect, almost identically, the dosing
equivalencies found in the pharmacological review. The
pricing perspective is a new methodology, made possible
by analyzing recently collected data from Colorado’s retail
marijuana market.
The information contained in this report is specifi c to
Colorado in 2015. Production techniques are constantly
evolving, and the marijuana included in this study was
Executive Summary
Equivalency Report 7 EXECUTIVE SUMMARYThe conversion factors described above are the fi rst of
their kind. They can be useful for state-level production
management. The conversions allow units of infused
edibles and concentrates to be denominated by fl ower
weight, and then added to fl ower sales, in order to
determine retail market demand and supply.
PHARMACOKINETIC EQUIVALENCY
An important compliment to the physical THC relation-
ships identifi ed in this study is the pharmacological
perspective. If the purpose of the equivalency legislation is
to limit transactions or possession to a reasonable “dose”
of concentrates and marijuana products for residents and
non-residents, then the medical effects described here
will be useful to construct a set of equivalencies between
marijuana product types.
Pharmacokinetic equivalency incorporates fi ndings from
medical and pharmacological publications to inform
marijuana stakeholders about the dosing process. The
authors created a new mathematical construct that can
compare ingested and smoked marijuana products in a
consistent manner.
The pharmacokinetic model compares inhaled and
ingested products using a dose ratio. The calculations
are based upon different uptake routes and speeds for
the psychoactive compounds related to marijuana use
(e.g., THC and 11-OH-THC). Other compounds, such
as cannabinoids, are not included here because the
legislation relates only to retail use. The base pharma-
cokinetic equivalency ratio is 1 to 5.71. This means that
one milligram of THC in edible form, is equivalent to 5.71
milligrams of THC in smokable form.
Table ES-1. One Ounce Equivalents by Solvent Type
Source: Author calculations based on metrc™ data.
1-Ounce Flower Equivalents
Physical Equivalency THC Equivalency
Amount Amount Amount Amount
Edibles Concentrate (g) Edibles Concentrate (g)
Solvent Type (10mg) (Avg. Potency) (10mg) (Avg. Potency)
Butane 391.07 5.46 434.35 6.91
CO2 346.96 4.84 434.35 8.07
Butter/Lipid 413.49 N/A 434.35 N/A
Ethanol N/A 5.44 N/A 7.37
Water N/A 3.10 N/A 8.50
8 Equivalency ReportEXECUTIVE SUMMARYtypical prices for the products themselves. The middle
portion shows the price after conversion—in cents per
milligram THC (₵/MGTHC). Finally, the bottom portion
computes the price-ratio between products using the
THC price measure.
Table ES-3 shows the price of marijuana fl ower, or buds,
is $14.03 when purchased by the gram, or $264 when
an ounce is purchased. When converted to THC, the
same product costs 8.25 cents per milligram THC when
purchased by the gram, and 6.10 ₵/MGTHC for an ounce,
refl ecting some volume-pricing. Similarly, a typical 100mg
THC edible product costs $24.99, a 40mg product is
$19.81, and a single-serve 10mg THC edible costs $6.60.
When converted, the THC price for these products equals
24.99 ₵/MGTHC, 35.00 ₵/MGTHC, and 66.00 ₵/MGTHC
respectively, for these goods. Finally, concentrates cost
$55.00 for a typical 1 gram wax portion, and a typical
500mg vaporizing cartridge costs $66.00. The THC
prices are 8.46 ₵/MGTHC and 18.86 ₵/MGTHC, respectively.
Using the THC prices, the edibles to fl ower price ratio is
3.03 (edible THC per fl ower THC) for the 100mg edible
product, 3.00 for the 80mg product, and 4.24 for the 40mg
product. The 10mg single-serving ratio is 8.00, which we
believe refl ects a minimum price for small portions.
Table ES-2 shows the pharmacokinetic equivalencies,
and the corresponding serving equivalencies, using data
from Colorado.
Pharmacokinetic equivalencies indicate that 83 ten-
milligram infused edible products is equivalent to one
ounce of marijuana fl ower in Colorado. About 7.72
grams of concentrate is equivalent to an ounce of fl ower
marijuana.
MARKET PRICE EQUIVALENCY
For comparison, a third equivalency approach was
developed by the study team. This is the “market price
equivalency” method. As with the physical equivalencies,
this methodology was previously not possible. We use
metrc™ data to convert retail store market prices into a
price per unit of THC across different products. These
new THC-based prices refl ect the inherent value of each
product from a psychoactive dose viewpoint. They reveal
the price that consumers are willing to pay for the psycho-
active experience (the high) yielded from each type of
product.
Table ES-3 below shows representative marijuana product
pricing in Colorado’s retail market. The top portion shows
Table ES-2. Pharmacokinetic Dosage Equivalency
Source: Author calculations based on metrc™ data.
Average THC
Potency
Effective Uptake
Ratio
1 Gram
Equivalent
1 Ounce
Equivalent
Buds/Flower 17.1% 1.00 1 Gram 1 Ounce
Edibles N/A 5.71 3 Servings 83 Servings
Concentrates 62.1% 1.00 0.28 Grams 7.72 Grams
Equivalency Report 9 EXECUTIVE SUMMARYThe ratio for wax/shatter is 1.03 for a 1 gram container,
and 2.28 for a 500mg vaporizer cartridge. The higher
price ratio for vaporizing equipment may refl ect higher
packaging costs.
In general, the price ratios shown in Table ES-3 are
notable because they match—quite closely—to the phar-
macokinetic equivalency ratios. This means that although
the market participants may not have completed their
own pharmacokinetic research, they naturally have gravi-
tated toward this result, based simply upon trial and error.
The remainder of this report provides details regarding
the data, the methodologies, and previous scientifi c
fi ndings used to construct our results.
10 Equivalency ReportEXECUTIVE SUMMARYTable ES-3. THC Market Price Equivalencies
Note: 1. Prices taken from a sample of online retail menus for Colorado stores.
2. Ratios may not necessarily apply to other states..
Source: Colorado Storefront menus, calculations by the report study team.
THC Market Price Ratios in Colorado
Indicative Prices by Weight ($)
Buds/Flower
1 Gram 1/8 Oz 1/4 Oz 1 Ounce
Most Common $14.03 $41.27 $82.54 $264.14
Discounted $12.38 $33.03 $66.06 $239.43
Edibles
100 MG 80 MG 40 MG 10 MG
Edible Variety $24.99 $19.81 $14.00 $6.60
Concentrates
1 Gram 500 MG 250 MG
Wax / Shatter $55.00 -- -- --
Vape Cartridge -- $66.00 $46.00 --
Equivalent Market Price (Cents per MG THC)
Buds/Flower
1 Gram 1/8 Oz 1/4 Oz 1 Ounce
Most Common 8.25 6.94 6.94 6.10
Discounted 7.28 5.55 5.55 5.53
Edibles
100 MG 80 MG 40 MG 10 MG
Edible Variety 24.99 24.76 35.00 66.00
Concentrates
1 Gram 500 MG 250 MG
Wax / Shatter 8.46 -- -- --
Vape Cartridge -- 18.86 26.29 --
THC Market Price Equivalencies (Price Ratios in THC Units)
Buds/Flower
1 Gram 1/8 Oz 1/4 Oz 1 Ounce
Most Common 1.00 1.00 1.00 1.00
Edibles
100 MG 80 MG 40 MG 10 MG
Edible Variety 3.03 3.00 4.24 8.00
Concentrates
1 Gram 500 MG 250 MG
Wax / Shatter 1.03 -- -- --
Vape Cartridge -- 2.28 3.19 --
Equivalency Report 11 SECTION ISECTION IISECTION IIISECTION IVSECTION VThe fi rst perspective is from a physical production view-
point, where servings of infused edibles or concentrates
are converted into the respective weight of marijuana
fl ower or trim needed as inputs to production. To construct
these equivalencies, average yield and potency is esti-
mated by the consultants after a series of interviews with
Marijuana Infused Product (MIP) manufacturers, and by
analyzing the state’s Marijuana Enforcement Tracking
Reporting Compliance (metrc™) database to isolate input
and output packages at MIPs for various concentrates
and infused edibles. This metric will provide a bridge
between concentrate and infused edible output and plant
material inputs.
The second perspective computes equivalencies from
a dosing viewpoint. The dosing perspective provides
stakeholders with a pharmacological model that equates
the dosing effect between inhaled and ingested mari-
juana products. The pharmacological approach resolves
the disparity between weight-based THC content in mari-
juana products, so that a dose-equivalent measure can
be established.
Finally, the third perspective computes the market price
of THC across product types in the Colorado market-
place. The pricing perspective is a new methodology. It
was made possible by manipulating recently collected
data from Colorado’s retail marijuana market. By using
statewide inventory and testing data, the study team can
convert retail marijuana store price for fl ower, concen-
trates, and infused edibles into a price with a common
denominator—THC. The study team found that the pricing
structure in stores refl ects, almost exactly, the phar-
macokinetic dosing equivalencies found in this report.
This suggests that although no individual has explicitly
measured the dosing effect of different products, that the
marketplace refl ects the dosing value for each product
implicitly.
The original legislation to legalize and regulate marijuana
in Colorado for adult use did not include explicit purchase
restrictions on marijuana concentrates and infused
edibles. As these marijuana products grew more popular
in 2014, up to 35 percent1 of statewide retail sales, legis-
lation was enacted under House Bill 14-1361 to remedy
the omission. The legislation does so by stipulating limits
upon marijuana fl ower portions, “or their equivalent.”
This study provides unbiased, scientifi c information
that can be used to suggest appropriate equivalencies
between fl ower and alternative marijuana products. It
is a summary of how different marijuana products are
produced and consumed in accordance with House Bill
14-1361, which requires the state to conduct a study to
establish equivalencies.
The information in this study can be used to convert
concentrate and infused products into their fl ower weight
equivalents from both a production and consumption
viewpoint. From a production viewpoint, the fi ndings can
be used to translate marijuana product unit sales into their
weight equivalent. This will improve the measurement
of aggregate marijuana demand, by using a common
denominator. From a consumption viewpoint, the fi ndings
here can be used to establish an equivalent “dose”
amount between non-fl ower products and fl ower weight.
Overall, the study is designed to meet the requirements
of House Bill 14-1361 and focuses solely on the retail
adult-use marijuana market. Issues related to medical
marijuana are not addressed in this study.
PRODUCTION, PRICE, AND DOSING
EQUIVALENCIES
This study investigates marijuana equivalencies from
three perspectives: production, price, and dosing.
1 Based upon statewide retail sales, May – September 2014.
Overview and Motivation
12 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION Vremove outliers and questionable records. The sample
sizes used in the analysis represent the largest samples
we could pull from the system that we believed would
give reliable results.
The report is organized as follows: Section II provides
a summary of prevailing MIP production techniques,
followed by the calculation of production equivalencies
in Section III. In Section IV, a pharmacokinetic model
is developed and dosing equivalencies are defi ned.
Section V explains the market price equivalency methods
and fi ndings, and Section VI provides a brief summary of
the study fi ndings. Following Section VI is a dictionary of
marijuana terms used here, as well as a reference list for
the interested reader.
The science and data related to marijuana, its use, and
regulation are inherently complex. The purpose of this
report is to synthesize state-level marijuana data with
existing manufacturing and medical research in order to
construct easy-to-understand ratios between marijuana
product types. The resulting information can be used
to establish a set of rules that are defensible, operable,
transparent and systematic. Over time, as new information
evolves, these fi ndings may be reviewed and adjusted to
refl ect the most current research available.
This analysis and report is developed for use by stake-
holders in Colorado’s retail marijuana market. It is assumed
that the reader of this report is an informed, intelligent
public policy offi cial or individual with experience and
understanding of Colorado’s retail and medical marijuana
markets. The objective of this report is to provide a clear
and understandable synthesis of relationships between
marijuana product types.
USE OF METRC™ DATA
This study would not have been possible before the state
inventory tracking system was established. The system
allows a viewpoint of the entire state marketplace from
“seed to sale”, providing a powerful data arena from
which to determine key statistics, such as potency levels,
production ratios, and consumption rates, to name a few.
Colorado’s inventory tracking platform, metrc™, requires
data to be uploaded from every cannabis business. As
a result, there is some underlying variability due to user
input error by MIPs, cultivations, and retail stores.
During this study and during previous studies over the
past 18 months, the study team has reconciled most
disparities by conducting thorough checks, and through
vendor interviews to ensure that data is being interpreted
correctly. Over the course of this research, the investi-
gators applied generally accepted statistical methods to
Equivalency Report 13 SECTION ISECTION IISECTION IIISECTION IVSECTION Vthrough various refi ning techniques to produce a refi ned
oil in various consistencies. Potential solvents include
hydrocarbons, carbon dioxide, butter/cooking oils/
lipids, ether, ethanol, isopropyl alcohol, water, and dry
extraction methods. Several extraction methods involving
hydrocarbons and carbon dioxide were borrowed from
long-standing methods used in the fragrance and food
industries.
Over the course of the interviews, it became apparent that
while any of the aforementioned solvents can produce
a marijuana concentrate or other infused product,
commercial producers prefer hydrocarbon, carbon
dioxide, and butter/lipid extraction processes. Inter-
viewees cited solvent costs, effi ciencies in production,
This section provides descriptions of marijuana infused
product concentrate production techniques used in
commercial MIPs in Colorado. The information contained
in this section was obtained through a series of interviews
conducted between April 24 and June 18, 2015.
The voluntary industry outreach process consisted of 11
in-person interviews, facility tours, and phone interviews
with MIP operators and testing facilities. No identi-
fying information of specifi c facilities is included in this
report to protect the privacy and intellectual property of
interviewees. The interviews consisted of the following
business types organized by primary production process:
• Butane/hydrocarbon concentrates (4);
• Carbon dioxide concentrates (2);
• Butter-based edibles (2);
• Butane/hydrocarbon edibles (2); and
• Carbon dioxide edibles (1).
In addition to the individual interviews, the study team
attended two industry group meetings at the request of
the Marijuana Industry Group (MIG) and the Cannabis
Business Alliance (CBA). The meetings allowed member
businesses to ask questions and provide their input to the
study in group format.
PRODUCTION TECHNIQUE
SUMMARY
Several cannabinoid extraction techniques are used
in the production of marijuana concentrates and
edibles. The majority involve using a solvent process
where solvents are introduced to marijuana plant material
to form a concentrate. The solvents are then removed
THC vs. THCa
Marijuana fl ower is often said to contain THC,
but this is not technically true. The plant
contains “THCa”, which is not psychoactive
in its natural state. THC is created through
decarboxylation.
Decarboxylation is the process of heating
THCa, which naturally occurs in cannabis
plants, to activate THC that can be absorbed
in the body through ingestion. In the process,
the THCa loses carbon and oxygen mole-
cules, and about 12.3 percent of its weight.
This weight reduction is calculated using the
molecular weight of THCa and THC.
Although the report authors refer to both THC
and THCa throughout the report, the reader
can interpret the terms as synonomous.
Prevailing MIP Production
Techniques
14 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION Vand output product quality as reasons for using these
preferred solvents.
Metrc™ data confi rmed that these three solvents account
for over 93 percent of edibles production in the state.
The interview participants used variations on the three
major solvent processes shown above. Each process is
described in more detail below.
HYDROCARBON EXTRACTION
PROCESS
Hydrocarbon extraction uses any number of hydro-
carbons as the principal solvent. Butane and propane are
the most common solvents used in commercial opera-
tions. When cannabis plant matter comes in contact with
the hydrocarbons; cannabinoids, terpenes, and other
compounds dissolve into the solvent. The hydrocarbon
solvent and cannabinoid mixture is purged using vacuum
ovens to remove the solvents.
The purging process leaves only cannabinoids and other
desired compounds in a refi ned concentrate. Hydro-
carbon concentrates are often called butane hash oil
Table II-1. Butane Extraction Weight Yields and THCa Potency
Product Type Primary Input
Input Potency
(% THCa) Weight Yield (%)
Output Potency
(% THCa)
MIP 1 BHO Wax/Shatter Trim 12-20 12-22 60-80
MIP 2 BHO Wax/Shatter Trim 15-20 10-25 70-95
MIP 3 BHO Wax/Shatter Trim 10-20 10-20 65-90
MIP 4 BHO (edibles) Trim 10-17 15-20 65-80
Source: MIP interviews April - June 2015.
(BHO), shatter, or wax. All of these products refer to
slightly different refi ning techniques that occur after the
BHO is extracted from the plant matter. BHO and other
variants contain a high concentration of THCa, often
between 60 percent and 95 percent, depending on the
amount of refi nement and quality of inputs.
If BHO is used to make infused edible products, it must be
decarboxylated. Decarboxylation converts the THCa in
cannabis plants into psychoactive THC. Decarboxylation
requires heating the BHO to 240°F–250°F until bubbling
dissipates to achieve desired results. BHO sold for
smoking or vaporizing does not require decarboxylation.
Table II-1 shows information on weight yields and THCa
potency for hydrocarbon extractions obtained during the
industry outreach process. Weight yield is the ratio of
output weight to input weight. THCa potency is obtained
from metrc™ as part of the mandatory testing for potency
and safety. Table II-1 presents THCa for all establishments
regardless if the end product is a concentrate or edible.
Equivalency Report 15 SECTION ISECTION IISECTION IIISECTION IVSECTION VThe refi ning process removes plant waxes, chlorophyll, or
other undesirable elements.
Similar to BHO, CO2 oil contains THCa concentrations
between 60 percent and 85 percent, depending on the
amount of refi nement and quality of inputs.
CO2 extractions must be decarboxylated to make edible
products. An increasing number of edible products are
made with decarboxylated CO2 oil as the active ingre-
dient. The decarboxylation process with CO2 oil is similar
to BHO.
Table II-2 shows weight yields and THCa potency for
CO2 extractions obtained during the industry outreach
process. Table II-2 presents THCa for all establishments
regardless if the end product is a concentrate or edible.
BUTTER AND COOKING OILS
Perhaps the most widely known method for extracting
cannabis for edible preparations involves the use of
butter, coconut oil, and other cooking oils. Cannabinoids
are fat soluble, and MIPs add cannabis to butter and
other oils and the mixture is heated to 240°F–250°F.
CARBON DIOXIDE EXTRACTION
PROCESS
Carbon dioxide (CO2) fl uid extraction techniques have
been used for various industrial applications in the food
and cosmetic industries. CO2 at very high (supercritical)
or low (subcritical) pressures is used to extract canna-
binoids from plant material. Different combinations of
temperature and pressure are used in the extraction.
CO2 is a popular solvent due to its lack of toxicity and
its perception as a less dangerous form of cannabis
concentrate. CO2 oils are a popular ingredient in vapor-
izing concentrates for use with a stationary vaporizer or a
portable vaporizer pen.
CO2 fractionations2 at different pressures in the production
process can yield different product consistencies and
compositions. Plant waxes remain in varying amounts
in the raw extraction, which is often refi ned further using
various techniques involving an ethanol wash or refrig-
eration techniques called winterization.
2 Fractionation is a separation process in which a certain quantity of
a mixture (gas, solid, liquid, suspension or isotope) into a number of
smaller quantities (fractions) in which the composition varies accord-
ing to a pressure or temperature gradient.
Product Type Primary Input
Input Potency
(% THCa) Weight Yield (%)
Output Potency
(% THCa)
MIP 1 CO2 Oil Trim 12-17 10-15 80-85
MIP 2 CO2 Oil Trim 15-17 8-12 70-80
MIP 3 CO2 Oil (edibles) Trim 10-15 8-10 60-65
Table II-2. CO2 Extraction Weight Yields and THCa Potency
Source: MIP interviews April - June 2015.
16 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VProduct Type Primary Input
Input Potency
(% THCa) Weight Yield (%)
Output Potency
(% THC)
MIP 1 Butter edibles Trim 10-15 3-4 1.9-2.5
MIP 2 Butter edibles Trim 15-22 2.75-3.25 2.0-2.8
Table II-3. Butter and Oil Extraction Weight Yields and THCa Potency
Source: MIP interviews April - June 2015.
While these methods are employed in Colorado for some
commercial production, no MIPs in the interview group
reported use of these methods on a commercial scale.
These extraction methods are in use for small production
batches and represent less than 7 percent of the market.3
The interviewees often referred to these products as a
“cottage” or “artisanal” market.
In the following section, metrc™ data is used to provide
production equivalency calculations for alcohol and water
based extraction methods in addition to the methods
encountered in the interviews (hydrocarbon, CO2, and
butter/oil).
3 Based upon author calculations from metrc™ data.
Some MIPS vary this process by decarboxylating the
plant material before adding it to the butter. Then plant
material is strained and the butter is brought back to room
temperature.
MIPs are required to test each batch of cannabis butter
or oil for potency. After a batch of butter is made and
tested for potency, the MIP may add additional butter or
oil if necessary to adjust the potency in accordance to
its recipe. Then the cannabis butter or oil is measured in
the recipe to determine the appropriate potency for each
batch of baked edible products. The butter MIP oper-
ators indicated that they have formed relationships with
wholesale suppliers for trim, and they generally know the
potency range of their raw cannabis butter, but natural
variation exists in each package of plant material used to
produce butter-based edibles.
Table II-3 shows weight yields and THC potency for butter
and oil extractions obtained during the industry outreach
process.
OTHER SOLVENTS
Marijuana concentrates and infused products can also be
manufactured using a host of other solvents, including
isopropyl alcohol, ethanol, vegetable glycerin, water, and
dry/solventless (kief).
Equivalency Report 17 SECTION ISECTION IISECTION IIISECTION IVSECTION VThe study team built a genealogy of packages that traces
them through the production process and correlates input
packages of trim and fl ower to output packages of mari-
juana concentrates and infused products at MIP facilities.
Once an input and output package is linked, the study
team mines the state inventory data to obtain identifying
information about the production process and package
contents. Equivalency calculations are provided for
extraction processes that use butter and cooking oils,
butane/hydrocarbons, CO2, water, and alcohol/ethanol
as primary solvent. The calculations provide information
on the yield on weight and input/output THC amounts for
each production process.
For example, in butane hash oil (BHO) manufacturing, if
a production batch starts with 1,000 grams of trim and
yields 180 grams of BHO, then we calculate a weight
yield of 18 percent. The study team then queries the
testing database to obtain THCa and THC fi gures for trim,
fl ower, concentrates, and edibles to obtain potency infor-
mation for production inputs and outputs. The process
diagram in Figure III-1 shows the data collection process
in metrc™ for weight yield and potency.
In this section, metrc™ data is used to identify statewide
average conversions of marijuana plant inputs into mari-
juana product outputs. Together with the MIP production
structure defi ned above, these two sections combine to
produce conversion rates between plant-based inputs
and infused or concentrated outputs.
The study team developed two types of physical equiva-
lency calculations: a simple THC conversion and a more
nuanced physical conversion. The physical conversion
traces the marijuana through the concentrate and edible
production process and matches inputs (marijuana
plant material) with outputs (concentrates and infused
products). The THC conversion presents a more basic
equivalency that quantifi es equal amounts of THC in
marijuana concentrates, edibles, and plant material. The
equivalencies are organized by the major solvents used
in production.
Inventory tracking data is used to trace the path between
cultivation centers, marijuana infused products (MIP)
manufacturers, and fi nal retail centers. Disparate data
sources needed to be translated and combined in order
to complete this task. For example, marijuana packaging
data provides information about product contents and
source, facility information is used to categorize package
owners and transfers. Transfer manifests provide an
accounting of shipments of intermediate and fi nal
products between facilities, and testing results are used
to establish potency among product types.
After plants are harvested and cured, marijuana fl ower
and trim are registered as “packages.” The packages are
transferred to retail stores for sale or to MIPs for further
processing. Package records contain identifying infor-
mation about package contents and the facilities on either
end of a package transfer.
Physical Equivalency Calculations
18 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VFigure III-1. Physical Equivalency Calculation Process
●Output package
●Concentrate amount (g)
●Input amount use (g)
●Category name
(concentrate)
●Extraction method
●Category name
(bud, shake/trim)
INPUT PACKAGE
REPACKS
OUTPUT PACKAGE
FACILITY INFO
PACKAGES
TRANSFER & REPACKS
YIELD ON WEIGHT
By extraction method (solvent)
THC/THCa POTENCY
By extraction method (solvent)
POTENCY TEST
POTENCY TEST
Equivalency Report 19 SECTION ISECTION IISECTION IIISECTION IVSECTION VThe fi gures in Table III-2 show between 9.7 and 17.1
percent concentrate weight yield rates on non-butter
solvents with relatively narrow confi dence intervals.
Using butane as an example, a 1,000-gram production
batch of trim yields on average 171 grams of BHO with a
mean potency of 71.7 percent THCa. These calculations
have a sample size of over 11,500 for weight yield and
over 5,600 for potency.
The calculation process provides the weight yield and
potency fi gures in Table III-2. Table III-2 provides the
mean weight yield, 95 percent confi dence interval range
and sample size for each solvent type included in the
analysis. Table III-2 also provides information on potency
testing for each solvent type. Marijuana fl ower and shake/
trim potency is also included.4
4 Testing results display combined THCa and THC for each solvent
type. Butter and oil potency is listed as amounts of THC due to decar-
boxylation. All other solvent types contain almost exclusively THCa.
Solvent
Yield Calculations Potency Calculations
Bud %
Shake/
Trim %
Mean
Weight
Yield
95%
Lower
Bound
Weight
Yield
95%
Upper
Bound
Weight
Yield (n)
Mean
THC/
THCa
%
95%
Lower
Bound
% THC/
THCa
95%
Upper
Bound
% THC/
THCa (n)
Butane 17.11% 16.76% 17.46% 11,514 71.67% 71.20% 72.14% 5,606 11.43% 88.57%
CO2 15.18% 14.80% 15.55% 7,257 61.39% 60.27% 62.51% 1,950 3.51% 96.49%
Butter 504.50% 484.69% 524.32% 599 2.57% 2.04% 3.09% 216 9.72% 90.28%
Water 9.72% 9.01% 10.43% 1,270 58.30% 56.34% 60.26% 266 9.91% 90.09%
Alcohol/
Ethanol 17.06% 14.37% 19.76% 241 67.17% 64.08% 70.25% 201 16.46% 83.54%
Flower 17.47% 17.41% 17.53% 26,023
Shake/Trim 15.53% 15.26% 15.80% 1,591
Table III-2. Marijuana Concentrate Yield and Potency
Source: Author calculations based on metrc™ data.
20 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VThe butter “yield” rate differs from other solvents because
it is a different production process. The butter yield
results can be interpreted as the weight of cannabis
butter produced per weight of plant input. For example,
100 grams of cannabis in a production batch would yield
on average 502 grams of cannabis butter at a mean THC
of 2.57 percent or 25 mg of THC per gram of butter.)5
The yield and potency fi gures described above are inputs
to the physical equivalency calculations. For concentrates
sold or transferred directly to retail stores, the fi gures in
Table III-2 provide the information for an equivalency. For
marijuana edibles, these fi gures are supplemented by
several intermediate calculations shown in Table III-3.
All fi gures from Table III-2 are converted from percentages
into milligrams per gram, as shown in Table III-3. This
conversion is necessary because edibles in the adult use
5 The butter yield rate was the most difficult to interpret because of
the many weight units that can be used to describe the prepared can-
nabis butters. There is also the possibility that some manufacturers re-
port the output units after additional non-psychoactive butter is added
to the cannabis butter. The 5-to-1 yield ratio is somewhat higher than
what was discussed in our interviews. The authors have elected to use
the metrc™ data due to the amount of data (1,623 records) that sup-
port the figures in Table III-2.
Table III-3. Edibles Intermediate Calculations
Source: Author calculations based on metrc™ data.
Solvent
mg THC/g
Solvent
g Solvent per
10 mg Edible
g Trim per 10
mg Edible
Butter 25.70 0.39 0.08
Butane 716.70 0.014 0.08
CO2 613.90 0.016 0.09
retail market are sold in two standard sizes (10mg and
100mg)6 based on the amount of THC contained in the
edible product.
The calculations in Table III-3 show the average potency
of each solvent used in edibles production, the amount
of solvent necessary to produce an edible product with
10mg of THC, and the amount of marijuana plant material
necessary to produce 10mg edible product. On average,
between .08 and .09 grams (or 80–90 mg) of plant material
is required to make an edible product containing 10mg of
THC.
Table III-4 shows equivalency calculations based on the
physical approach described in Table III-3. Equivalencies
are organized by solvent type and shown for edibles
and concentrates. The process estimates the amount of
plant material used in each 10 mg and 100 mg edible
package and provides a calculation of the amount of
edible packages that can be produced from an ounce of
dried marijuana fl ower.
For concentrates available directly for sale, the study team
provides estimates of the amount of plant material used
to make one gram of concentrate at average potency for
each solvent type. Similar conversions for an ounce and a
quarter-ounce of marijuana fl ower are provided.
Table III-4 provides estimates of the amount of trim used in
each production process and then converts trim amounts
to fl ower equivalents using a THC-based conversion
factor derived from the testing data presented in Table
III-2.7
6 Two dosages are outlined in state statute. One is 10mg., which
represents a standard dose of THC. The second is 100 mg., which
contains 10 servings and represents the maximum amount of THC
allowed in an edible retail marijuana infused product.
7 Trim has on average 15.53 percent THC and flower has on aver-
age 17.47 percent THC; therefore, a conversion ratio is calculated at
1.125.
Equivalency Report 21 SECTION ISECTION IISECTION IIISECTION IVSECTION VALTERNATE METHODOLOGY
A second, simpler methodology is presented in Table
III-5 that employs THC as the common unit for conversion
between the various forms of marijuana products. This
methodology calculates an equivalent amount of THC in
various forms of marijuana products based on the testing
information shown in Table III-2.
The equivalency factors in Table III-5 can be interpreted
as showing units with equivalent amounts of THC. For
instance, given the uniform dosage amounts of edibles
The physical equivalencies in Table III-4 show that about
between 347 and 413 edibles of 10 mg strength can be
produced from an ounce of marijuana, depending on the
solvent type and production method. For concentrates,
between 3.10 and 5.50 grams of concentrate are equiv-
alent to an ounce of fl ower marijuana.
The conversion factors described above can be useful
for state-level production management. The conversions
allow units of infused edibles and concentrates to be
expressed in equivalent fl ower weight, and then added to
fl ower sales, in order to determine retail market demand
and supply.
Product Type Solvent
Purchase
Amount
Trim Used in
Production
Flower
Equivalency
Ratio
Ounce
Equivalent
Quarter-Oz
Equivalent
Edible Butter 10 mg 0.08 g 0.07 g 413.49 each 103.37 each
Edible Butter 100 mg 0.77 g 0.69 g 41.35 each 10.34 each
Edible Butane 10 mg 0.08 g 0.07 g 391.07 each 97.77 each
Edible Butane 100 mg 0.82 g 0.72 g 39.11 each 9.78 each
Edible CO2 10 mg 0.09 g 0.08 g 346.96 each 86.74 each
Edible CO2 100 mg 0.92 g 0.82 g 34.70 each 8.67 each
Concentrate Butane 1 g 5.84 g 5.20 g 5.46 g 1.36 g
Concentrate CO2 1 g 6.59 g 5.86 g 4.84 g 1.21 g
Concentrate Ethanol 1 g 5.86 g 5.21 g 5.44 g 1.36 g
Concentrate Water 1 g 10.29 g 9.15 g 3.10 g 0.77 g
Table III-4. Physical Equivalency Calculations
Source: Author calculations based on metrc™ data.
22 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VTable III-5. Simple THC Equivalency Calculations
Source: Author calculations based on metrc™ data.
Product Type Solvent
Purchase
Amount
THC
Amount
THCa
Amount
Flower
Equivalency
Ratio
Ounce
Equivalent
Quarter-Oz
Equivalents
Edible Butter 10 mg 10 mg 11.40 mg 0.07 g 434.35 each 108.59 each
Edible Butter 100 mg 100 mg 114.03 mg 0.65 g 43.43 each 10.86 each
Edible Butane 10 mg 10 mg 11.40 mg 0.07 g 434.35 each 108.59 each
Edible Butane 100 mg 100 mg 114.03 mg 0.65 g 43.43 each 10.86 each
Edible CO2 10 mg 10 mg 11.40 mg 0.07 g 434.35 each 108.59 each
Edible CO2 100 mg 100 mg 114.03 mg 0.65 g 43.43 each 10.86 each
Concentrate Butane 1 g 0.72 g 0.72 g 4.10 g 6.91 g 1.73 g
Concentrate CO2 1 g 0.61 g 0.61 g 3.51 g 8.07 g 2.02 g
Concentrate Ethanol 1 g 0.67 g 0.67 g 3.84 g 7.37 g 1.84 g
Concentrate Water 1 g 0.58 g 0.58 g 3.34 g 8.50 g 2.12 g
For retail concentrates equivalency calculations, the THC/
THCa conversion is not necessary because concentrates
are not decarboxylated for direct retail sale. The THC in
one gram of concentrate is equivalent to between 3.05g
and 3.75g of marijuana fl ower at average potency. Ounce
and quarter-ounce equivalents are also provided in Table
III-5.
in Colorado, all 10mg strength edibles have an amount of
THC equivalent to 60 mg (0.06 g) of fl ower marijuana at
the average potency. A conversion rate of 1.14 is applied
to convert THC in infused products back to THCa in
fl ower due to weight loss in the decarboxylation process
involved in manufacturing edibles.8
8 Decarboxylation is the process of heating THCa, which naturally
occurs in cannabis plants, to activate THC that can be absorbed in
the body through ingestion. In the process, the THCa loses a carbon
dioxide molecule and about 12.3 percent of its weight. Conversion
calculation from THC back to THCa uses 1/(1-.123) or 1.14. This
weight reduction is calculated using the molecular weight of THCa
and THC obtained from Steep Hill Labs http://steephilllab.com/re-
sources/cannabinoid-and-terpenoid-reference-guide/.
Equivalency Report 23 SECTION ISECTION IISECTION IIISECTION IVSECTION VTHC derivatives) can be delivered to the recipient in a
number of ways. Each method translates into a different
net amount of THC entering the bloodstream and the
brain.
• Flower smoking: Over the past 30 years, smoking
has been the most common method to consume mari-
juana. Based upon 2014-15 data, the THC content in
Colorado retail fl ower lies between 8-22 percent, with
a mean estimate of roughly 17 percent. Therefore,
one gram of marijuana fl ower contains 170 milligrams
of THC, on average. However, a large portion of
that THC is destroyed during the smoking process.
In this report, we itemize the uptake rates and the
potential loss of THC through smoking, during the
process of inhalation, exhaling, and blood-clearance.
The process is further complicated by the transfer
process of THC from the blood plasma, into the brain
itself.
• THC ingestion: Alternatively, THC can be infused into
edible products such as baked goods or candies, and
then eaten. By state law, each serving of edibles is
limited to no more than 10 milligrams of THC content.
THC, when ingested, will be absorbed at different
levels, depending upon other foods in the stomach,
and upon the chemical nature of the pre-existing
foods. As with smoked products, a majority of the
THC is not absorbed by digestion. Various studies,
which will be discussed below, suggest that between
6-20 percent of the THC content in an edible product
is metabolized and absorbed into the bloodstream.
However, ingestion and processing by the liver has
been found to create an important THC byproduct that
subsequently boosts the psychoactive effect of THC.
This research will be discussed later in this section.
An important compliment to the physical THC relation-
ships identifi ed in this study is the pharmacological
perspective. If the purpose of the equivalency legislation is
to limit transactions or possession to a reasonable “dose”
of concentrates and marijuana products for residents and
non-residents, then the medical effects described here
will be useful to construct a set of equivalencies between
marijuana products.
There are several methods to consume marijuana such
as intravenous, oral mucosal, ingested, transdermal, and
inhaled. The two most popular methods for consumption
are ingestion and inhalation. We focus upon these two
methods in this study. The remaining methods are either
reviewed briefl y or are provided as references for the
interested reader.
The reader should understand that this section does
not represent a clinical study. Instead, this section uses
fi ndings from other studies to inform marijuana stake-
holders about the dosing process, and it provides a
new mathematical construct that can compare ingested
and smoked marijuana products in a consistent manner.
Therefore, this report should be considered to be a policy-
driven study that leverages medical literature to provide
scientifi c evidence during the construction of dose equiv-
alencies between various marijuana products.
This section focuses upon the psychoactive components
of marijuana, primarily THC and related chemicals, and
does not focus upon the medicinal effects of marijuana
because the fi ndings and resulting regulations will be
applied only to Colorado’s retail marijuana market, under
House Bill 14-1361.
ENUMERATION OF THC UPTAKE
METHODS FOR MARIJUANA
The psychoactive component of marijuana, THC (and
Pharmacological Equivalencies
24 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION Vrelationship between THCa and THC is explained at the
beginning of this report.
THC itself is the primary psychoactive component in
marijuana, but there are also related chemicals that have
been found to have an amplifi cation effect upon the base
blood levels of THC. In particular, when THC is ingested,
it is then oxidized and converted by the liver into the
active metabolite named 11-hydroxy-THC (11-OH-THC)
[see 23, 25], and 11-nor-9-Carboxy-THC (THC-COOH),
a secondary, non-psychoactive metabolite.10 Recent
studies have found that 11-OH-THC penetrates the
brain barrier more quickly than regular THC, causing a
markedly-higher psychoactive effect. We cite a number
of studies below, to estimate the relative potency of
11-OH-THC versus regular THC in blood levels, in order
to more accurately characterize the psychoactive effects
between ingestion and inhalation of THC.
IDENTIFICATION OF THC UPTAKE
AND BENCHMARKING
This section describes THC uptake, delivery methods,
and related dosing. The dosing relationships between
uptake methods (smoking and ingesting) can be quite
different from the physical weight relationships that were
identifi ed in the fi rst half of this report. One relationship is
pharmacokinetic, while the other is purely physical.
Comparing Peak Effect vs. Aggregate Effect
It is also important to recognize the differences between
“peak effects” or “aggregate effects.” The former measure
identifi es the most intense moment experienced by a
subject during a dosage event with marijuana. This can
10 THC-COOH is a non-psychoactive metabolite formed in the liver
when THC is ingested or smoked. Due to its inactive nature, it is not
factored into equivalency calculations See source 9 in references
section.
• Concentrate smoking or “dabbing:” This method
also uses smoking as the uptake method, but the
material contains very high concentrations of THCa.
The typical THC content in concentrated forms of mari-
juana varies between 60-80 percent, although rates as
high as 95 percent have sometimes been observed. By
heating and smoking these concentrates, the uptake
ratios are similar to smoking marijuana fl ower, but the
ratios of THC to fl ower-based cannabinoids may be
different, creating a different type of psychoactive effect.
THC, THCA, 11-OH-THC AND
THC-COOH9
The underlying chemistry for marijuana, and its psycho-
active elements is complex and beyond the policy
scope of this report. A large number of clinical studies
and medical fi ndings are cited later in this section. This
subsection provides a brief and concise overview of the
main psychoactive component in marijuana, THC. In
addition to THC, there are cannabinoids, typically labeled
using a root form, CBD, and then enumerated, such as
“CBD-A” or “CBD-B.” Many cannabinoids contain psycho-
active elements as well, but the type of effect caused by
those cannabinoids is not typically as strong as THC.
Because this study is designed for the retail market, and
not the medical market, only the psychoactive THC and
THC related chemicals are considered.
The reader is reminded that marijuana fl ower (or buds)
does not contain THC itself, but instead contains THCa
(Tetrahydrocannabinolic Acid), a precursor to THC. The
9 Please note that this sub-section is an overview of report findings.
In order to be concise, only a few of the specific technical references
and citations are provided here. Instead, most citations are provided,
combined, and enumerated during the longer, technical exposition at
the bottom of this section.
Equivalency Report 25 SECTION ISECTION IISECTION IIISECTION IVSECTION Vbe characterized as the “peak intensity” of the high. The
latter measure calculates the integral, or area under the
curve where the curve relates to blood-levels of THC and
11-OH-THC over time.
Typically, smoking produces a higher peak effect, as THC
enters the blood stream through lung tissue. But THC
levels are also quickly reduced when smoked, as the
body works to clean contaminants from the bloodstream.
Conversely, edible products absorb much more slowly, so
that the effect is delayed compared to smoking. However,
the digestion and oxidization process last much longer.
For example, Figure IV-1 shows the THC and related
chemicals in the blood stream over time. As shown,
THC concentrations peaked 90 minutes after ingestion,
and 11-OH-THC peaked slightly later, at approximately
110 minutes. Levels of these psychoactives remained
elevated for approximately 300 minutes, or fi ve hours,
and non-active THC-COOH remained elevated for 1,400
minutes (almost 24 hours).
In contrast, smoking concentrations were much higher,
and shorter. Figure IV-2, taken from the “California NORML
Guide Interpreting Drug Test Results,”11 combines results
from smoking and ingested THC to reveal the relative
magnitude of blood plasma levels.
11 Sourced from: http://www.canorml.org/healthfacts/drugtestguide/
drugtestdetection.html#fn03. Last visited on June 13, 2015.
Figure IV-1. An
Example of Blood
Plasma Concentration
Rates of THC
Derivatives Over Time,
After Oral Ingestion of
Marijuana Products.
From Nadulski et. Al.
(2005).
26 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VIndeed, for the psychoactive effects to occur, the THC
must penetrate the blood-brain barrier and connect
directly to the brain. This means that even though blood-
plasma THC levels are 10 times higher when smoking
versus ingesting THC, the psychoactive effect may not
be 10 times as intense, because THC is not necessarily
reaching the brain at the same rate as it fl ows in the blood
plasma.
As discussed earlier, 11-OH-THC has an extenuating
effect. According to Perez-Reyes, et. al. [26], it has been
found to penetrate the brain membrane approximately
four times faster than THC. This suggests 11-OH-THC will
contribute more rapidly to the psychoactive effects than
THC. Also, by elongating the amount of time that THC is
elevated in the blood plasma when THC is ingested and
processed by the liver, there is more time for the THC
Figure IV-2 shows that THC plasma concentrations
are more than 10 times higher for smoked cannabis
compared to ingested cannabis. The more recent fi ndings
from Nadulski, et. Al. (2005) suggest that while THC and
11-OH-THC levels peak much earlier than suggested by
Law, et al. (1984), the relative magnitudes are similar.
Peak levels were 5-6 ng/mL in the Nadulski study, and
approximately 8 ng/mL in the Law study.
These fi ndings suggest that either smoked marijuana
experiences are signifi cantly more intense, or—as scien-
tists suggest—that 11-OH-THC produces an extenuated
effect, compared to base THC. It also suggests that
the relationship between blood-plasma THC levels do
not necessarily correspond to psychoactive effects in a
strictly-linear fashion.
Figure IV-2. Comparison of
Inhaled Versus Ingested THC
Elements
References:
(A-B) Smoked dose based on data
from M. Huestis , J. Henningfield and E.
Cone,M. Huestis , J. Henningfield and
E. Cone. [08] M. Huestis , J. Henning-
field and E. Cone,“Blood Cannabinoids.
I. Absorption of THC and Formation
of 11-OH-THC and THCCOOH During
and After Smoking Marijuana”, Journal
of Analytic Toxicology, Vol. 16: 276-282
(1992).
(C) Oral dose based on data from B.
Law et al. ([03] B. Law et al, “Forensic
aspects of the metabolism and excre-
tion of cannabinoids following oral
ingestion of cannabis resin,” J. Pharm.
Pharmacol. 36: 289-94 (1984).)
Equivalency Report 27 SECTION ISECTION IISECTION IIISECTION IVSECTION Vblood is slower, as discussed earlier. Next, the so-called
“High perfusion” tissues begin absorbing THC, followed
by “Low perfusion” tissues, and fi nally, fat tissues.
ROLE OF THE BLOOD-BRAIN-
BARRIER (BBB)
A barrier, or sheath, separates the brain from the human
body blood stream. There are several descriptions of the
BBB.12 In general, the BBB is a highly selective permeable
12 See, for example: Blood-Brain Barrier: Drug Delivery and Brain
Pathology, edited by David Kobiler, Shlomo Lustig, Shlomo Shapira,
2012. Springer Science & Business Media, Dec 6, 2012. A clear
description for the lay person can also be found on Wikipedia: https://
en.wikipedia.org/wiki/Blood%E2%80%93brain_barrier. Accessed on
June 16, 2015.
to penetrate the brain membrane and therefore a higher
ratio of absorption of THC and other psychoactives into
the brain fl uid.
Together, this suggests that lower concentrations of THC
in blood plasma do not necessarily imply that consumers
are experiencing a lower intensity of psychoactivity.
Instead, the level of THC and 11-OH-THC, combined with
the time these metabolites have to penetrate the blood
brain barrier, will determine the comparative psycho-
active effects between inhaling and ingesting marijuana
products.
The different rates of tissue absorption are shown more
clearly in Figure IV-3. Here, blood plasma levels are the
immediate recipients of THC, yielding high rates of THC
concentration. However, rate of brain absorption from the
Figure IV-3. Distribution
of THC in the Body.
Blood and Brain
Absorption Rates Differ
Signifi cantly.
References:
Nahas, G. G. (1975) Marijuana: toxicity
and tolerance. In Medical Aspects of Drug
Abuse (ed. R. W. Richter), pp. 16-36. Balti-
more, MD: Harper & Row.
28 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION V“effective” THC within the brain itself. The share of THC
that actually passes through the BBB and into the brain
during the short period when blood-plasma levels are high
is estimated to be approximately 35 percent. Just over
one-third of the THC in the blood plasma is captured by
the brain before it is cleaned out by the body’s pulmonary
system.
CONSTRUCTING DOSING
EQUIVALENCIES FOR MARIJUANA
PRODUCTS
This is the fi rst time that data from an offi cial marijuana
market is combined with medical research to develop
scientifi cally-based relationships between marijuana
products. The estimates refl ect the best-available data
and knowledge as of the report publication. Over time,
we hope that further research can be used to improve
upon the methods here, and to refi ne the estimates as
knowledge of the subject matter continues to improve.
In order to synthesize the various pharmacokinetics of
marijuana uptake into a simple, actionable metric, we
suggest using a THC conversion factor. The conversion
factor for purposes of dosing will compare the amount of
weight-based THC contained in smokable products, such
as marijuana fl ower and concentrates, with the amount of
weight-based THC contained in ingested THC products
such as edibles.
For example, if the THC conversion factor for dosing
equals 1:5, this means that one milligram of THC in
edible form (ingested) is roughly equal, from a dosing
perspective, to 5 milligrams of THC in a smokable form.
This section will provide a basic conversion factor model
that synthesizes the scientifi c fi ndings discussed earlier,
in order to construct the THC conversion model.
barrier that separates the circulating (pulmonary) blood
from the brain extracellular fl uid that circulates in the
central nervous system. The blood–brain barrier is formed
by brain endothelial cells, which are connected by tight
junctions with a high electrical resistivity. The BBB allows
water and some gases to pass through, as well as lipid-
soluble molecules. It also allows the selective transport
of molecules, such as glucose and amino acids that are
crucial to neural functioning. The BBB will often prevent
the entry of lipophilic, potential neurotoxins by way of the
so-called active transport mechanism. A small number of
regions in the brain do not have a blood–brain barrier.
The BBB is an important factor that limits the fl ow of THC
between the body’s blood plasma and the brain, where it
creates the psychoactive effects. Where THC is allowed
to penetrate the BBB, the rate of penetration is slow. In
contrast, scientists have found that the rate of penetration
for 11-OH-THC is much faster.
The selective permeability of the BBB causes a compe-
tition. On the one hand is the BBB/THC passage rate
allowed by the BBB, and on the other hand is the meta-
bolic clearance rate for toxins in blood-plasma. The BBB
slowly allows THC to pass through the membrane, causing
the psychoactive effects. But at the same time, the body’s
metabolism will purify the blood stream, rapidly removing
the THC from blood-plasma.
This competition causes a decrease in THC effectiveness
from inhalation, compared to the slower, steadier THC
supply from ingestion. As shown in Figure IV-2, the
concentration of THC in the blood stream is much higher
when inhaled than when ingested. But due to blood
plasma clearance, the ratio quickly falls to relatively low
levels (e.g., in 30 minutes).
The limitations incurred by the BBB suggest that much of
the THC in the blood-plasma is therefore lost, because
the BBB slows conversion of blood-plasma THC into
Equivalency Report 29 SECTION ISECTION IISECTION IIISECTION IVSECTION VFor edibles, a similar approach can be used. Edibles
come in various shapes and sizes, but are required to
contain 10 milligrams or less of THC per serving. This
allows for a direct uptake comparison of THC content into
effective THC uptake from ingestion.
In edibles, the metabolism of THC into 11-OH-THC
is an important consideration. It is also important to
acknowledge that the slow, steady release of THC and
11-OH-THC into the blood stream allows most, if not all,
of the THC derivatives to pass through the BBB. Thus,
the equation below implicitly assumes a blood-brain THC
retention share of 100 percent for edible marijuana.
The total uptake equivalent, UE, is a function of the THC
absorption rate in the stomach, θ, and amount of THC in
the product, by weight, ω. Next, the absorbed portion
of THC is metabolized into two components, THC and
11-OH-THC, where THC enters the blood stream linearly,
but 11-OH-THC, which can pass the BBB more rapidly,
receives a conversion factor, y.
As with inhaled THC, the share ratio of THC uptake can
be constructed simply by dividing by the weight of the
THC content in the product:
Finally, a simple equivalency ratio can be derived from
the share-value uptake ratios. This equivalency ratio, R,
is used to denote the relative psychoactive effect that is
embodied in edible versus smokable marijuana products.
The THC conversion factor is based upon a combination
of fi ndings. Among them are: the typical THC loss rate
during the smoking process; the typical loss rate of THC
for ingested products; the absorption rate of THC vs.
11-OH-THC in the brain; and the estimated comparative
psychoactive intensity of THC versus 11-OH-THC.
For clarity, the uptake relationship can be parameterized
and displayed mathematically. The following equations
explain the relationship between each pharmacoki-
netic fi nding and the overall impact of that fi nding upon
the equivalency factor between inhaled and ingested
products.
First, the effective uptake of THC or THC derivatives from
inhalation can be simplifi ed using the following formula:
The total uptake U, is the product of the fl ower weight,
w, times the THC/THCa content. This yields the THC
weight available for inhaling. This amount is then scaled
by the share of THC captured during the inhalation, αΙΝ,
and also by the share of THC retained in the lungs after
exhalation, αΕΧ. These inputs determine the level of THC
that will ultimately be absorbed into the subject’s blood
plasma. Finally, the share of THC that passes through the
BBB from the blood-plasma is denoted by β. The product
of these parameters reveals the effective THC uptake
from inhalation of activated THC.
The uptake ratio for the THC content alone can be
obtained by simply dividing by the marijuana fl ower
weight and THC concentration (cw). After doing this, we
denote uI to be the uptake conversion factor. It is:
30 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VFor the purposes of this study, R is the key ratio that
can be used to compare edible products with smokable
products, from a policy standpoint.
IDENTIFICATION OF PARAMETER
VALUES
Each of the parameters in these equations has been
studied to some degree. Some studies are directly
relevant to specifi c parameter values, while others are
only tangentially relevant, since they were each written for
different purposes than this equivalency study. Relevant
studies are cited numerically and are included in the
references section. For these reasons, this study utilizes
a range of values that is based on existing research. This
range of values is used to determine a point estimate for
the equivalency ratio (R), which is the equivalent dose
impact of 1 milligram of THC in edible form, in milligrams
of THC in smokable form.
Studies related to αΙΝ and αΕΧ
The physical uptake of THC through smoking has been
Symbol Table
Symbol Description Relevant Literature
U, u
Uptake equivalent amount of THC, in weight
terms, and unit-free terms, for edibles (E), and
for inhalation (I).
Calculated as a function of parameterized values
from this report.
C THC concentration rate in marijuana fl ower.Based upon testing observations from Colorado
retailers and dispensaries.
W Weight of marijuana fl ower.
αΙΝ, αΕΧ
Share of captured THC during marijuana
smoke inhalation, and after exhalation,
respectively.
Scientifi c laboratory studies of marijuana smoking.
See See [20], [30], [31].
β Brain fl uid retention rate from blood plasma.
θ Absorption rate of THC when ingested in the
form of an edible product.
[25], [24], [21], [19], and [13] are studies on oral
consumption of marijuana, and its effects upon the
human body.
ω Weight of THC in edible form, in milligrams.
y Effective impact of 11-OH-THC that is
metabolized by the liver.
Pharmacokinetic studies by [5], [1], [2], [21], and
[26].
R
Equivalency ratio – the equivalent dose
impact of 1 milligram of THC in edible form, in
milligrams of THC in smokable form.
Calculated as a function of parameterized values
from this report.
Equivalency Report 31 SECTION ISECTION IISECTION IIISECTION IVSECTION Vbioavailability of a smoked dose of THC is between the
range of 0.10 and 0.25.“
[10] “Bioavailability following the smoking route was
reported as 2−56%, due in part to intra- and inter-subject
variability in smoking dynamics, which contributes to
uncertainty in dose delivery. The number, duration, and
spacing of puffs, hold time, and inhalation volume, or
smoking topography, greatly infl uences the degree of
drug exposure.”
[8] “The apparent absorption fraction calculated in the
current study was in a similar range of previous fi ndings on
THC, showing an oral bioavailability of 6 %, and inhalation
of 18 % (frequent smokers) or 23 % (heavy smokers).”
[5] “A systemic bioavailability of 23 ± 16% and 27 ± 10%
for heavy users versus 10 ± 7% and 14 ± 1% for occa-
sional users of the drug was reported.”
[7] “Pulmonary bioavailability varies from 10 to 35
percent of an inhaled dose and is determined by the
depth of inhalation along with the duration of puffi ng and
breath-holding.”
Studies related to β
The role of the blood brain barrier (BBB) in THC and
11-OH-THC uptake is an important factor in determining
equivalencies, as this function limits the fl ow of THC
between the body’s blood plasma and the brain, where it
creates the psychoactive effects. As previously indicated,
where THC is allowed to penetrate the BBB, the rate of
penetration is slow. Below is a section from M. Huestis
(2007)[10], that highlights the diffi culty of THC passing
through the BBB:
“Adams and Martin studied the THC dose required to
induce pharmacological effects in humans. They deter-
mined that 2−22 mg of THC must be present in a cannabis
discussed as part of various marijuana smoking experi-
ments. Numerous studies examine the absorption of THC
through smoking cannabis. The results of these studies
vary, with one study putting the range of absorption from
2 percent - 56 percent. A study by Perez-Reyes found
that absorption varied widely due to various factors,
including marijuana potency, the amount of unchanged
THC available in the smoke inhaled, amount of THC lost in
side-stream smoke, method of smoking (i.e., cigarette or
pipe) and the amount of THC passed through the upper
respiratory tract. [12] A thorough examination of these
studies leads to a more reasonable range of absorption
through smoking of 10-25 percent. [5, 2, 10, 8, 7] This
value range will be used in this study for calculations
related to smoking equivalencies.
Below are relevant excerpts from the medical literature,
related to the uptake ratios of inhalation and exhalation
for THC absorption:
[12] “The factor of absorption from smoking varies in
terms of THC uptake and the actual amount of THC that is
absorbed through smoking of marijuana. The factors that
affect uptake ratios of smoking include, (1) the potency of
the marijuana smoked; (2) the amount of unchanged THC
present in the smoke inhaled (i.e., the amount of THC not
destroyed by pyrolysis); (3) the amount of THC lost in
side-stream smoke; (4) the method of smoking (cigarette
vs. pipe smoking); and (5) the amount of THC trapped in
the mucosa of the upper respiratory tract. These iden-
tifi ed factors have made exact uptake ratios of THC
diffi cult to determine, and therefore studies to this point
have produced a range of THC absorption.”
[2] “Past studies indicate that smoking cannabis turns
approximately 50% of the THC content into smoke, with
the remainder lost by heat or from smoke that is not
inhaled. Up to 50% of inhaled smoke is exhaled again,
and some of the remaining smoke undergoes localized
metabolism in the lung. The end result is that the estimated
32 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VTHC can be observed up to seven days after dosing.13
Based upon the slow BBB permeability, and the relatively
rapid blood clearance rate, this study assumes that only
a portion, equal to 35 percent, of THC blood plasma
levels end up being absorbed by receptors in the brain
when smoking. The comparative rate for ingestion will be
much higher, as the liver metabolizes THC more slowly,
leading to a long, sustained level of blood plasma THC
and 11-OH-THC.
Studies related to θ
The process of THC absorption through ingestion is more
straightforward. While there can be variation in this value,
depending upon the stomach contents, rate of metab-
olism and a number of other factors [2,13]. Grotenhermen
and Schwilke et al. fi nd that the rate lies between 6-12
percent absorption, while Borgelt, Franson, Nussbaum,
and Wang suggest that the rate is between 5-20 percent,
with the rates typically on the lower range of absorption.
Given this information, this study assumes 10 percent as
a reasonable rate of THC absorption through ingestion.
[2, 6, 13] These studies conclude that the absorption
rate of THC through oral administration will be typically
be less than that of smoking, with metabolism of THC
into 11-OH-THC in the liver as a key factor in the low
absorption of THC in this process.
13 Most of this literature is motivated to identify specific cutoff points
to be considered legally “intoxicated” by THC and similar compounds.
A non-psychoactive derivative of THC is 11-nor-9-carboxy-THC (THC-
COOH), which is the most common trace substance used to detect
marijuana use. New research focuses upon THC and 11-OH-THC
since allowable levels are now needed, rather than presence alone.
Colorado, for example, has a 5 µg/liter “permissible inference” law, as
a cutoff value for legal intoxication of marijuana.
cigarette to deliver 0.2−4.4 mg of THC, based on 10−25%
bioavailability for smoked THC. Only 1% of this dose at
peak concentration was found in the brain, indicating that
only 2−44 μg of THC penetrates to the brain.” [Section
2.2: Distribution]
The competition between blood plasma concentra-
tions and brain tissue concentrations is described by
researchers as hysteresis, an indication that the cognitive
effects of THC do not occur immediately when THC
blood-plasma levels are elevated, but instead, they occur
after the THC has been absorbed by various body tissues
(primarily, the brain). The dosing effects are said to occur
after the blood level and tissue THC concentrations are
equal. The following passage from Cone and Huestis
(1993) describes this:
“THC is rapidly absorbed and distributed to tissues;
initial changes in blood concentrations are out of phase
(hysteresis) with physiological and behavioral changes.
Once blood/tissue equilibrium is established, a direct
correlation of THC blood concentration and effect is
observed.” [Abstract]
Several studies that were motivated by THC driving
impairment purposes have measured the rate of blood
plasma clearance. An example is Hartman, et. al. (2015),
this team measures the blood plasma clearance for
THC after dosing THC using a vaporizing pen. The early
clearance of THC was shown to be rapid, with concen-
tration rates falling from a peak of 60 μg/liter 10 minutes
after dosing, down to 15 μg/liter 30 minutes after dosing
(and 20 minutes after the peak), and then to approxi-
mately 8 μg liter 90 minutes after dosing. Small levels of
Equivalency Report 33 SECTION ISECTION IISECTION IIISECTION IVSECTION Van average potency of 17 percent.14 This implies that just
over 0.5 grams (588 milligrams) of typical marijuana fl ower
in Colorado contains 100 milligrams of THC (or THCa).
From the worked example, an equivalent 100 milligrams
of THC from an edible product would yield the equivalent
effect of 3,361 milligrams (or 3.36 grams) of marijuana in
fl ower form.
Due to each of the pharmacokinetic effects that are
presented in this study, 100 milligrams of THC content in
a smokable form, yields 7.88 milligrams of THC into the
brain itself. In contrast, 100 milligrams of THC content in
edible form yields a much higher ratio of 45.0 milligrams.
14 Based upon 28,023 laboratory test samples reported between
October 2014 and May 2015.
A WORKED EXAMPLE
For concreteness, a worked example is provided in Table
IV-4. This example compares the uptake ratios for THC
derivatives for 100 milligrams of THC that is either inhaled
or ingested.
The result from Table IV-4 is that the equivalency ratio,
R, equals 5.71, after fi ndings from the medical literature
are used to calibrate each of the uptake ratio parameters.
This means that one milligram of THC in edible form, is
equivalent to 5.71 milligrams of THC that is available in
smokable form.
In the example above, which is based upon observa-
tions taken from metrc™, marijuana fl ower, or bud, has
Differential Uptake Equivalency: Inhaled vs. Ingested THC 100 mg Example
Inhaled THC from Marjiuana Flower Ingested THC from Edible
THC in Smokable Flower 100 Edible Package: (100 MG) 100
THC Content 17% Rate of Absorption 10%
% of Content Inhaled 50% THC absorption (mg) 10
% of Inhaled Air Exhaled 45% 11-OH-THC Conversion 3.5
Gross THC Absorption (mg) 22.5 11-OH-THC / THC Equivalent: 35.00
Blood Cycle De-Rate Factor 35%
Effective THC Infusion to Brain (mg) 7.88 Effective THC Infusion to Brain (mg) 45.00
Equivalencies
Flower Weight (mg) 588 Flower Weight Equivalent (mg) 3,361
THC Equivalancy Ratio 1 THC Equivalency Ratio 5.71
Table IV-4. Example of Marijuana Equivalency Between Inhaled and Ingested Uptake Methods
Source: Author’s calculations, combined with published medical research findings and statistical data from metrc™.
34 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VThe equivalency ratio, R, can now be combined with THC
content in various products, in order to construct more
user-friendly conversion factors between product types.
Table IV-5 lists common weights of marijuana fl ower that
are purchased from retail and medical outlets in Colorado.
Next to these weights are the number of units, based
upon serving size, that are considered “equivalent” from
a dosing perspective. For example, the purchase limit for
an out-of-state patron at a retail marijuana store is one
quarter of one ounce. This purchase limit would corre-
spond to 21 units or servings of THC in edible form. If the
edible is packaged in 100 milligram packages, then two
100 milligram packages could be purchased, plus one
10 milligram unit. That would fulfi ll the patron’s daily limit
purchase amount of marijuana.
For enforcement purposes, residents and non-residents
alike are allowed to possess up to one ounce of mari-
juana fl ower at a given time. This one ounce amount
corresponds to 83 units or servings of edible products. It
can be packaged in the form of eight 100 mg packages
of servings, plus three 10 mg additional individually-
wrapped servings.
One gram of smokable marijuana corresponds to three 10
mg servings of edible products.
Of course, any combination of these amounts is also
possible. For example, an out of state patron can
purchase 1/8 ounce of marijuana fl ower, and can also
purchase 10.5 servings (105 mg) of THC in edible form.
Similarly, a resident who is 21 years or older could legally
possess ½ ounce of marijuana fl ower, plus another 41.5
servings of THC in edible form.
For concentrates, the ratio of concentrate THC to fl ower
THC is “one to one,” because both are inhaled. Thus,
the conversion factors between smoked concentrates
(e.g., “dabbing”) and smoked fl ower products are based
solely upon the THC potency embodied in the weight of
Conversion Factors
Edibles (Weight to 10mg Units)
0.25 Oz of Flower equals: 21 10mg Edible Units
1 Oz of Flower equals: 83 10mg Edible Units
1 Gram of Flower equals: 3 10mg Edible Units
Concentrates (Weight to Weight)
0.25 Oz of Flower equals: 1.9
Grams
Concentrate
1 Oz of Flower equals: 7.7
Grams
Concentrate
1 Gram of Flower equals: 0.3
Grams
Concentrate
Potency
(THC share of weight)62%Based upon
metrc™ Data
Figure IV-5. Conversion Factors between
Marijuana Flower Weight and Non-fl ower
Product Units
Source: Author’s calculations, combined with medical literature
findings and metrc™ data.
As discussed earlier, this is caused by a number of
factors, including the time-curve of THC and 11-OH-THC
blood-plasma levels in the blood and the share of that
THC that can pass through the blood brain barrier.
RESULTING EQUIVALENCY TABLES
For policy purposes, Table IV-5 is constructed to compare
different quantities of fl ower to their equivalent edible
serving sizes. Concentrates are also included, using
the average potency found from laboratory testing in
Colorado between October 2014 and May 2015.
Equivalency Report 35 SECTION ISECTION IISECTION IIISECTION IVSECTION Vthe product itself. In Colorado, the average concentration
ratio for wax or shatter type concentrates was 62 percent,
based upon data collected between October 2014 and
May 2015. Using this ratio, combined with the 17 percent
average THC ratio in Colorado marijuana fl ower, the
smoked THC conversion factors can be easily computed.
For example, using the concentrate to fl ower THC ratios
above, the result is 62/17 = 3.65.
For concentrates, the daily limit corresponding to one-
quarter ounce of fl ower, is 1.9 grams of wax or shatter
concentrate. Similarly, one ounce of fl ower equals 7.7
grams of concentrate, and one gram equals 0.3 grams
of concentrate.
OILS, TINCTURES, LOTIONS, AND
LESS COMMON UPTAKE METHODS
In Colorado, the share of edibles and concentrates in total
demand has increased substantially. This demand growth
precipitated the need for further regulatory oversight for
these products. There also exists a large array of addi-
tional uptake methods for consuming marijuana. These
include the sublingual approach (using tinctures), dermal
(using lotions), and intravenous, among other methods.
These methods are not considered here, because a full
investigation into each method is beyond the scope of
this report, and because the current demand levels for
these methods are relatively low. If the demand shares for
these methods grows and becomes more important, then
some investigation is warranted.
36 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION Von the following page displays typical marijuana products
and prices for the Colorado recreational market.
How do we know that this product menu is “representative”
of other menus along the Front Range? From an economic
viewpoint, this menu is “representative” because the
market for marijuana is relatively competitive. If this menu
were signifi cantly more expensive, or signifi cantly less
expensive than other menus, then the company would not
sell much product, or they would be selling more product
than they can produce in a given period.
Similarly, if the relative pricing between product types
were skewed, then buyers would only purchase selected
items that are relatively inexpensive, and they would not
purchase the items that are relatively more expensive.
So, in addition to being “representative” in gross price,
the menu here is also representative in relative price—the
relationship between prices from this menu will be similar
to the offerings from most Colorado retail stores.
The prices listed in Table V-6 are displayed in terms of
gross weight – either for marijuana fl ower or the weight
of THC within a non-fl ower product. Until now, it was
not possible to compare different products in Colorado,
because there was no common denominator. However,
using metrc™ data, this study fi nds the average potency
of most popular marijuana strains to be quite narrow,
between 16.5 and 17.7 percent of THCa. Therefore, we
can use a midpoint value of 17 percent as the average
expected potency in Colorado marijuana fl ower sold at
the retail level.
Using this potency, the menu in Table V-6, listed in dollars
per weight or unit, can be converted into a uniform menu,
using the weight of THC (or THCa). The most convenient
unit of measure is “cents per milligram of THC” (₵/MGTHC).
There is a third method to consider equivalencies between
marijuana products in Colorado’s retail marijuana market.
This is the “market price equivalency” method. From an
economic viewpoint, this method is considered to be
more direct than other methods, because it compares the
price per unit of THC across different products, thereby
refl ecting the price that consumers are willing to pay—on
a THC basis—for each product type.
Until now, it was not possible to compare market prices
based upon THC content. By using mandated potency
tests for fl ower and concentrates, an average potency
rate can be applied, and then compared to edibles, which
are marketed with fi xed levels of THC content. Prices for
marijuana products are easily found on most storefront
websites.
Unlike many retail consumption products, the market for
marijuana is relatively homogeneous. This is different
from tobacco, where consumers identify products by
brand name (Marlboro, or Camels). The homogeneity of
marijuana suggests that market pricing should be based
primarily upon the potency of the drug, rather than by
advertising or marketing infl uences.
Most consumers of marijuana are purchasing the product
for its psychoactive properties. To the extent that the
product supplies more doses, the supplier can sell the
product at a higher price. Therefore, from an economic
viewpoint, there should be a positive, and relatively
linear, relationship between the psychoactive ingredient
provided by marijuana products and the price paid for
it. This relationship can be compared across different
product types, and used as supporting or detracting
evidence for the dosage equivalencies computed in the
previous section.
Recent marijuana prices were obtained from various
Colorado vendors, and a table of representative prices
has been constructed. The product menu in Figure V-6
Market Price Comparison
Equivalency Report 37 SECTION ISECTION IISECTION IIISECTION IVSECTION VRepresentative Recreational Menu Prices — June 15, 2015
Flower Price by Weight ($USD)
1 gram 1 eighth 1 quarter 1 half-oz 1 oz
Indica
Ghost OG 14.03 41.27 82.54 148.58 264.14
Triangle Kush X Ghost OG 14.03 41.27 82.54 148.58 264.14
Sativa
Glass Slipper 12.38 33.03 66.06 132.12 239.43
Hybrid
White Master Kush 14.03 41.27 82.54 148.58 264.14
KING CHEM 12.38 33.03 66.06 132.10 239.43
Edibles THC MG Price (each)
Highly Edible 100 mg 24.99
Incredibles Boulder Bar 100 mg 23.11
80 mg Dr. J’s AM capsules 80 mg 19.81
Gaia’s Garden Garden Drops 80 mg 19.81
Incredibles Peanut Budda 50 mg 19.81
40 mg Blue Kudu Chocolate 40 mg 14.00
Gaia’s Garden Single Serving Lollipop 10 mg 6.60
Gaia’s Garden Single Serving Karma Kandy 10 mg 6.60
Sweetgrass Snickerdoodle Cookie 10 mg 5.00
Concentrates THC MG Price (g)
O-Pen Vape Cartridge 500 mg 66.00
Co2 Oil 61.92
Mahatma Shatter 61.92
TC Labs Shatter (Strain Specifi c) 55.00
O-Pen Vape Cartridge 250 mg 46.00
Figure V-6. Market Pricing for Marijuana Products in Colorado, Priced in Dollars by Weight or by
Unit
Source: Marijuana storefront websites, accessed on June 15, 2015.
38 Equivalency ReportSECTION ISECTION IISECTION IIISECTION IVSECTION VThe price ratios shown in Table V-7 on the following
page are notable because they refl ect—quite closely—
the pharmacokinetic results found earlier. That is, the
standard market pricing for edibles, when compared by
THC content, has a 3:1 ratio, just as the product equiva-
lency tables would suggest. This means that although the
market participants may not have completed their own
pharmacokinetic research, they naturally have gravitated
toward this result, based simply upon trial and error.
Of course, there are some products at the edge of the
pricing structure, where the price ratio for THC is higher
than 3:1. For example, the “Single Serving Lollipop” is
priced at 66 ₵/MGTHC, which results in an 8:1 ratio. This
pricing relates mostly to the fact that pricing for very small
servings (e.g., single servings) have a lower bound, due
to packaging and marketing. The price of a single serving
lollipop is $6.60, mainly due to a lower price bound for
marijuana products in general. Products that contain
more than a single 10 mg serving of THC are all priced
more closely to the 3:1 ratio than the single-serving units.
To summarize, the market price method for equivalency
supports our earlier pharmacokinetic work. Market forces
have led to a pricing structure that refl ects a roughly 3:1
ratio between smoked THC products and edible THC
products.
Equivalency Report 39 SECTION ISECTION IISECTION IIISECTION IVSECTION VRepresentative Recreational Menu Prices — June 15, 2015
Flower Price: Cents per mg THC
1 gram 1 eighth 1 quarter 1 half-oz 1 oz
Indica Strains
Ghost OG 8.25 6.94 6.94 6.24 6.10
Triangle Kush X Ghost OG 8.25 6.94 6.94 6.24 6.10
Sativa Strains
Glass Slipper 7.28 5.55 5.55 5.55 5.53
Hybrid Strains
White Master Kush 8.25 6.94 6.94 6.24 6.10
KING CHEM 7.28 5.55 5.55 5.55 5.53
Edibles
Price:
Cents per mg THC Price Ratio: (per 1 g of Ghost OG)
Highly Edible 100 mg 24.99 3.03
Incredibles Boulder Bar 100 mg 23.11 2.80
80 mg Dr. J’s AM capsules 80 mg 24.76 3.00
Gaia’s Garden Garden Drops 80 mg 24.76 3.00
Incredibles Peanut Budda 50 mg 39.62 4.80
40 mg Blue Kudu Chocolate 40 mg 35.00 4.24
Gaia’s Garden Single Serving Lollipop 10 mg 66.00 8.00
Gaia’s Garden Single Serving Karma Kandy 10 mg 66.00 8.00
Sweetgrass Snickerdoodle Cookie 10 mg 50.00 6.06
Concentrates
Price:
Cents per mg THC Price Ratio: (per 1 g of Ghost OG)
O-Pen Vape Cartridge 500 mg 18.86 2.28
Co2 Oil 9.53 1.15
Mahatma Shatter 9.53 1.15
TC Labs Shatter (Strain Specifi c) 8.46 1.03
O-Pen Vape Cartridge 250 mg 26.29 3.19
Figure V-7. Comparison of Market Pricing Between Flower and Non-fl ower Products, Priced in
Cents per Milligram of THC Content
Note: Conversions based upon average potency for flower and concentrate products in Colorado, determined through required testing of flower
and concentrates.
Source: Colorado storefront menus, accessed on June 15, 2015.
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44 Equivalency ReportTERMS & ACRONYMSdesired for maximum potency and effect in edibles and
other infused products.
Infused product — A marijuana product which is
intended to be consumed orally, including but not limited
to, any type of food, drink, or pill.
Edibles — Any cannabis product which is consumed
orally and digested is considered an edible.
Hydrocarbon extractions — Any extraction process that
uses hydrocarbons such as butane or propane.
metrc™ — Marijuana Enforcement Tracking, Reporting
and Compliance is the required seed-to-sale tracking
system that tracks Retail Marijuana from either the seed
or immature plant stage until the Retail Marijuana or Retail
Marijuana Product is sold to a customer at a Retail Mari-
juana Store or is destroyed.
Marijuana Infused Product manufacturer (“MIP”) — An
entity licensed to purchase Retail Marijuana; manufacture,
prepare, and package Retail Marijuana Product; and sell
Retail Marijuana and Retail Marijuana Product only to
other Retail Marijuana Products Manufacturing Facilities
and Retail Marijuana Stores.
Supercritical extractions — When a substance is heated
and pressurized beyond its critical point, it turns into a
supercritical fl uid capable of working as a solvent to strip
away oils and essential compounds. It is used in a variety
of industries for botanical extractions with several different
types of fl uid, but in the cannabis world, it generally refers
to CO2 extractions. Supercritical extraction by nature is
not particularly selective in terms of what it extracts, so
many CO2 processors need to utilize a secondary solvent
such as ethanol or hexane in order to remove waxes and
chlorophyll prior to delivering a fi nished product.
Butane hash oil ( “BHO, dabs, shatter, wax”) — A non-
polar hydrocarbon which is used as a solvent in many
other industries such as essential oil extraction, butane is
especially well-suited for stripping cannabis buds or trim
of their cannabinoids, terpenes, and other essential oils
while leaving behind the majority of unwanted chlorophyll
and plant waxes. In this extraction method, the solvent
washes over the plant material and is then purged off
from the resulting solution using a variety of techniques
and variables such as heat, vacuum and agitation.
Cannabinoid — any of the chemical compounds that
are the active principles of marijuana. Cannabinoids
include THC, THCa, CBD, CBDa, CBN, and other natu-
rally occurring compounds.
CO2 extraction — When high pressure is applied to
CO2, it becomes a liquid that is capable of working as a
solvent, stripping away cannabinoids and essential oils
from plant material. This process is called supercritical
extraction and is the most common method of making
hash oil using CO2 instead of a hydrocarbon solvent such
as butane. CO2 extractions can take many of the same
textures as BHO, but generally they tend to be more oily
and less viscous.
Concentrate — Refers to any product which refi nes
fl owers into something more clean and potent. This
umbrella term includes any type of hash, solventless
(kief), as well as any hash oils (BHO, CO2 oil, shatter, wax,
etc.) and indicates that these products are a concen-
trated form of cannabis, carrying a much higher potency.
Decarboxylate — The process of converting THCa
and CBDa into THC and CBD is an essential part of the
process if you wish to consume cannabis orally. Decar-
boxylation occurs at around 240 degrees Fahrenheit,
converting THCa and CBDa into THC and CBD, respec-
tively. Though the acid forms of these cannabinoids have
some medicinal benefi ts, normally decarboxylation is
Terms & Acronyms
Equivalency Report 45 TERMS & ACRONYMSTHC — Tetrahydrocannabinol (THC) is the main canna-
binoid found in the cannabis plant and is responsible
for the majority of the plant’s psychoactive properties.
THC has lots of medical benefi ts including analgesic
properties, though perhaps its most defi ned quality is its
tendency to increase appetite. CBD acts as an antagonist
to THC, reducing its psychoactive effects.
THCa — Tetrahydrocannabinolic acid (THCa) is the most
prominent compound in fresh, undried cannabis.The
compound does not have psychoactive effects in its own
right, unless it is decarboxylated and converted into THC.
Trim — After harvest, the cannabis plant is generally
trimmed of its leaf matter, leaving behind only the buds.
Trimming refers to the actual act of removing the leaves,
while trim refers to the leftover leaves, which can be used
for making concentrates and infused products.
Vacuum purge — After extraction, most concentrates
require further refi ning in order to remove the solvent
which is remaining in the product. In order to do this,
concentrate makers have utilized vacuum ovens and
devices which serve to reduce the atmospheric pressure
on the concentrate, which speeds up the process of
removing the solvent.
Starting in 2017 the State of California will begin issuing Licenses based on
cannabis businesses that have already secured the following Local Permits:
CULTIVATION
Type 1 - Outdoor
5,000 sq ft
Type 2 - Outdoor
5,001 sq ft - 10,000 sq ft
Type 3 - Outdoor
10,001 sq ft - 1 Acre
Type 1A - Mixed Light
5,000 sq ft
Type 2A - Mixed Light
5,001 sq ft - 10,000 sq ft
Type 3A - Mixed Light
10,001sq ft - 22,000 sq ft
Type 1B - Indoor
5,000 sq ft
Type 2B - Indoor
5,001 sq ft - 10,000 sq ft
Type 3B - Indoor
10,001sq ft - 22,000 sq ft
Type 1C
Type 4 - Nursery - Non Flowering Plants - NO Plant Count
MANUFACTURING
Type 6 - Manufacturer 1 - Non-Volatile Solvents - Water Hash, Live Rosin, CO2
Type 7 - Manufacturer 2 - Light Hydrocarbon Extraction - Butane, Propane, and Hexane
TESTING
Type 8 - Testing - All Cannabis and Cannabis Products will need to be tested.
DISPENSARY; GENERAL & MIXED LICENSE TYPES
Type 10 - Dispensary - Brick and Mortars
Type 10A - Dispensary; No more than three sites. - Also known as the 3:1:4 Model, 3 Dispensaries, 1
Manufacturing, and up to 8 x 22,000 sq foot grows.
DISTRIBUTION/TRANSPORT HUB
Type 11 - Distribution - Think alcohol distribution model.
Type 12 - Transporter - Going to have to move it in secure vehicles until it is descheduled by the DEA.
slonorml.org
“Are you ready?”
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slocountynorml@gmail.com - 805-464-7420 - facebook.com/SanLuisObispoNORML/