This study investigates the demographics, marijuana use, and perceived risk associated with individuals' attitudes toward marijuana legalization in Michigan, particularly focusing on those who are unsure about their stance. The findings indicate that older adults and those who perceive marijuana as risky are less likely to support legalization or be unsure about it, while younger individuals and those with recent marijuana use tend to favor legalization. Understanding these attitudes is crucial as states continue to consider marijuana legislation in future elections.

1. Characteristics Associated with Attitudes toward Marijuana
Legalization in Michigan
Jennifer D. Ellis, M.A.a, Stella M. Resko, Ph.D. b,c, Kathryn
Szechy, M.S.W.b, Richard Smith, Ph.D.b,
and Theresa J. Early, Ph.D.d
aDepartment of Psychology, Wayne State University, Detroit,
MI, USA; bSchool of Social Work, Wayne State University,
Detroit, MI, USA; cMerrill
Palmer Skillman Institute, Wayne State University, Detroit, MI,
USA; dCollege of Social Work, The Ohio State University,
Columbus, OH, USA
ABSTRACT
Support for legalization of marijuana has increased over the
past several years. While studies have
examined correlates of favoring marijuana legalization, less
attention has been placed on those
who are unsure about legalization, despite the potential ly
important role of this group as states
vote on legalization in upcoming elections. Using data from a
statewide sample of adults in
Michigan, this study examined whether those who support,
oppose, or are unsure about legaliza-
tion differed based on demographics, marijuana use, and
perceived risk associated with marijuana
use. Those who were older and perceived marijuana use to pose
a greater risk had lower odds of
being unsure about legalization (relative to opposing
legalization); those who were politically left
of center or centrist and those who reported lifetime marijuana
use had higher odds of being

2. unsure about legalization. Older respondents, women, and those
who perceived marijuana use to
be risky had lower odds of supporting legalization; those w ho
were politically left of center or
centrist, and those who reported recent or lifetime marijuana
use had higher odds of supporting
legalization. Better understanding correlates of being unsure
about marijuana legalization may
help inform political and prevention efforts as states continue to
vote on these issues.
ARTICLE HISTORY
Received 12 June 2018
Accepted 11 March 2019
KEYWORDS
Marijuana; cannabis;
legalization; perspectives
Introduction
Although marijuana is illegal under federal United States
(US) drug policy, state and local marijuana policies have
shifted dramatically over the past two decades (Millhorn
et al. 2009; Nielsen 2010). As of November 2018, 33 states
have legalized medical marijuana use and 13 states, as well
as several local jurisdictions, have decriminalized mari-
juana possession. Additionally, 10 states and the District
of Columbia have legalized recreational marijuana use for
adults over 21 years of age. Michigan became the first
Midwestern state to legalize recreational marijuana when
56% of its voters approved a November 2018 ballot mea-
sure. Other states are expected to vote on medical mar-
ijuana, marijuana decriminalization and recreational
legalization initiatives in future elections (Caulkins,
Kilmer, and Kleiman 2016). As of early 2018, medical

3. marijuana is supported by an overwhelming majority of
Americans (>90%) (Quinnipiac University/Poll 2018), and
as of October 2018, approximately two in three supported
legalization of recreational marijuana (McCarthy 2017).
Public opinion researchers have examined correlates
of support for recreational marijuana legalization. In
recent studies of adults, male gender (Galston and
Dionne 2013; Looby, Earleywine, and Gieringer 2007;
Musgrave and Wilcox, 2013; Nielsen 2010), minority
racial/ethnic status (Looby, Earleywine, and Gieringer
2007; Nielsen 2010), having children (Caulkins et al.
2012; Cruz, Queirolo, and Boidi 2016; Nielsen 2010),
and being politically liberal (Looby, Earleywine, and
Gieringer 2007; Musgrave and Wilcox 2013; Nielsen
2010), were associated with supporting recreational
marijuana legalization. In the past two decades, spend-
ing a greater amount of time engaged with media (e.g.,
watching television or reading the newspaper) also was
associated with favoring legalization, although this rela-
tionship was not observed prior to 1990, and may be
due to more positive depictions of marijuana in recent
years (Stringer and Maggard 2016). Other researchers
have found that residents of states and countries that
have legalized medical or recreational marijuana sup-
port legalization at higher rates than residents of states
or countries where marijuana is not legal (Sznitman
and Bretteville-Jensen 2015; McGinty et al. 2017);
Schuermeyer et al. 2014). Exceptions to this trend
have been seen in young adult samples where rates of
support for legalization of marijuana for recreational
use are high regardless of the state’s policies (Cohn
et al. 2017; Moreno et al. 2016).
Additionally, an individual’s own use of substances

4. contributes to their broader opinions on substance use
CONTACT Jennifer D. Ellis [email protected] Department of
Psychology, Wayne State University, 5447 Woodward Ave.,
Detroit, MI 48202
JOURNAL OF PSYCHOACTIVE DRUGS
2019, VOL. 51, NO. 4, 335–342
https://doi.org/10.1080/02791072.2019.1610199
© 2019 Taylor & Francis Group, LLC
http://orcid.org/0000-0002-3323-0190
https://crossmark.crossref.org/dialog/?doi=10.1080/02791072.2
019.1610199&domain=pdf&date_stamp=2019-09-25
issues (Hilton and Kaskutas 1991; Latimer et al. 2001;
Resko 2014; Wagenaar et al. 2000). Cruz, Quierolo, and
Boidi’s (2016) analysis of samples from the United
States, El Salvador, and Uruguay found that past mar-
ijuana use was among the strongest predictors for sup-
porting recreational marijuana legalization. Williams,
Van Ours, and Grossman (2011) analysis of the
Australian Drug Strategy’s National Household Survey
similarly found current and past marijuana use were
significantly associated with supporting recreational
marijuana legalization. A sample of adults living in
Houston found that frequency of past 30-day use of
marijuana, as well as use of other drugs, was associated
with supporting legalization of marijuana (Trevino and
Richard 2002). In a US-based sample of young adults,
Cohn et al. (2017) found past month use of alcohol,
tobacco, marijuana, and other drugs were associated
with greater likelihood of supporting recreational mar-
ijuana legalization.

5. Much of the research on attitudes toward recrea-
tional marijuana legalization has used binary measures
that force respondents to indicate support for or against
marijuana legalization; however, some research sug-
gests that a number of individuals are still undecided
about whether they believe marijuana should be lega-
lized (Geiger 2016). Individuals who are undecided
about legalization have the potential to play an impor-
tant role as they decide how to vote in future elections.
Therefore, characterizing those who are unsure about
legalization may be useful. Additionally, examining
perceived risk towards marijuana use as a potential
correlate of attitudes towards legalization is important,
as perceived risk of marijuana has decreased over time
in the United States (Okaneku, Vearrier, McKeever,
LaSala & Greenberg, 2015), as support for legalization
has increased.
The present study examines the extent to which recrea-
tional marijuana legalization was supported by adults in
Michigan, as well as factors associated with supporting,
opposing, and being unsure about marijuana legalization.
In line with previous work demonstrating that one’s own
substance use is associated with perspectives about lega-
lization (Cohn et al. 2017; Trevino and Richard 2002), we
hypothesized that past year marijuana users would be
more likely to favor legalization, whereas those with less
recent marijuana use would be more likely to be unsure.
Additionally, because political orientation has been
related to supporting or opposing marijuana legalization
(Looby, Earleywine, and Gieringer 2007; Musgrave and
Wilcox, 2013; Nielsen 2010), we expected that those who
identify as politically centrist would be more likely to be
unsure about legalization. Finally, because women have
historically been more likely to be opposed to marijuana

6. legalization, but otherwise tend to lean politically liberal
relative to men (Galston and Dionne 2013), we expected
that women would be more likely to oppose or be unsure
about legalization when given this option.
Methods
Sample and study procedures
The present study was exempted from the Wayne State
University institutional review board. Data were drawn
from an anonymous web-based survey conducted by the
Michigan Prevention Association (MPA). The MPA is
a statewide advocacy group focused on substance misuse
prevention. The purpose of the statewide survey was to
examine attitudes toward marijuana legalization in
Michigan. In 2008, Michigan voters passed a ballot mea-
sure to legalize medical marijuana. Ten years later,
Michigan voters passed a measure to legalize recreational
marijuana (November 2018). For the current survey, the
MPA recruited a sample of adults (ages 18+) in Michigan.
Recruitment emails were sent to community partners
(e.g., health-care providers, mental health providers,
city/county health departments, county substance abuse
coalitions, non-profit/government agencies serving
families or older adults). Ads also were placed online
(e.g., Facebook), and recruitment announcements were
made at community events (e.g., community meetings,
health fairs). Advertisements stated MPA was looking for
adults (ages 18+) in Michigan to respond to a brief survey
(5–10 min) regardless of their experiences with marijuana.
Data collection took place over a three-week period in
August and September of 2016, prior to Michigan voters
passing a ballot measure for marijuana legalization. As
a validity check for the online survey, the researchers

7. included “please leave this item blank” in the middle of
the survey and examined the length of time spent com-
pleting the survey. The recruitment efforts yielded
a sample of 2,608 participants, of which 2,190 passed
validity checks and had complete data for all relevant
study measures. This group of 2,190 was included in the
following analyses.
Measures
Survey questions were grounded in previous public opinion
and substance use survey research. The MPA steering
committee developed the survey with input from its mem-
bers who worked in non-profit and government agencies
that provide community-based substance abuse treatment
and prevention services. Because participants were not
provided incentives for survey participation, efforts were
made to ensure brevity.
336 J. D. ELLIS ET AL.
Marijuana legalization
Attitudes toward marijuana legalization were assessed
with a question from the Pew Research Center (Geiger,
2016) that asks: “Do you think marijuana should be
made legal for recreational use, or not?” Response
options adapted for this study were: “Yes, Legal”, “No,
illegal” and “Unsure”.
Demographic variables
Demographic questions were selected or adapted from
the 2015 National Survey on Drug Use and Health
(Substance Use and Mental Health Administration
2016). These self-report questions included gender

8. (male, female, or other), age, race or ethnic origin
(White/Caucasian, Black/African American, Latino/
Hispanic, American Indian, Asian/Pacific Islander,
Arab/Middle Eastern, Multiracial, Other), highest level
of education (less than high school diploma or general
education degree (GED), high school diploma/GED,
bachelor’s degree, or graduate degree), and whether
participants had children age 18 or under. Because
small portions of respondents endorsed Latino/
Hispanic, American Indian, Asian/Pacific Islander,
Arab/Middle Eastern, multiracial, or other race/ethni-
city, those participants were combined into an “Other
race” group. Political affiliation was assessed with
responses grouped into three categories: left of center,
right of center, and center/other, a framework that has
been used in other studies (e.g., Furnham and
Thomson 1996).
Marijuana use
Participants were asked to self-report the last time that
they used marijuana. Response options were never,
within the past year, and more than one year ago.
Perceived risk associated with Marijuana
Participants were asked to rate their agreement with four
items addressing perceived risks associated with mari-
juana use. The items said 1) “Marijuana use is harmless”
(reverse scored), 2) “Marijuana is addictive”, 3) “Using
marijuana poses serious mental health risks”, and 4)
“Using marijuana poses serious physical health risks.”
Responses were rated on a 4-point scale ranging from
1 = Strongly Disagree to 4 = Strongly Agree. Scores for
the items were summed to create a composite measure
assessing the perceived risks of marijuana use, which
demonstrated good reliability in the present sample
(α = .886). These items were developed for this study,

9. and were informed by existing research examining com-
mon perceived risks associated with marijuana use (e.g.,
Berg et al. 2015; Danseco, Kingery, and Coggeshall 1999;
Wilkinson et al. 2016).
Data analysis
Data were analyzed using SPSS version 25 (IMB Corp.
2017). Descriptive statistics were examined for all study
variables. We conducted bivariate analyses using Pearson’s
χ2 tests for categorical independent variables and Analysis
of Variance (ANOVA) for continuous independent vari-
ables to compare those who supported, opposed and were
unsure about marijuana legalization. Independent variables
included demographics (age, gender, race/ethnicity, having
children in household, education level), political orienta-
tion and substance use-related variables (current or past
marijuana use, perceived risk associated with marijuana
use). After examining the bivariate relationships,
a multinomial logistic regression model was conducted
where all correlates were examined simultaneously. Being
opposed to marijuana legalization was used as the reference
category. To investigate potential problems with multicol -
linearity, we conducted correlational (Spearman’s rho)
analyses of the predictor variables (Menard 2001). No
issues with multicollinearity were found.
Results
Descriptive statistics are presented in Table 1.
Participants ranged in age from 18 to 88 years, with
an average age of 45.37 years (SD = 13.39). The sample
was 71.7% female and 90.7% of the sample reported
their race as “white.” Just under half of the sample
(47.4%) supported legalization of recreational mari -
juana, 41.6% did not support legalization, and 11.1%

10. were unsure.
Bivariate relationships between variables of interest
and opinions towards marijuana legalization are
reported in Table 2. Given the uneven group sizes and
a violation of the homogeneity of variance assumption
for both age (p = .004) and perceived risk associated with
marijuana use (p = .001), post-hoc tests using the
Games-Howell statistic were performed for the
ANOVA models. The results of these tests indicated
that individuals who opposed legalization were more
likely to be older than those who were unsure about
legalization (Mean Difference = 3.43, p = .001) and
who supported legalization (Mean Difference = 4.36,
p < .001). Individuals who opposed legalization per-
ceived marijuana to be more risky than those who were
unsure about legalization (Mean Difference = 0.63, p <
.001) and those who supported legalization (Mean
Difference = 1.46, p < .001). Those who were unsure
about legalization reported significantly greater per-
ceived risk than those who supported legalization
(Mean Difference = 0.83, p < .001). In addition to these
findings, chi-square tests indicated that, at the bivariate
JOURNAL OF PSYCHOACTIVE DRUGS 337
level, gender, education level, political orientation, and
marijuana use were significantly associated with opi-
nions regarding legalization of recreational marijuana.
No differences were observed for race/ethnicity or being
a parent.
Results of the multinomial logistic regression analy-
sis are presented in Table 3. Politically left of center or

11. centrist views, past year marijuana use, and lifetime
marijuana use were associated with higher odds of
supporting legalization, relative to opposing
legalization. Older age, female gender, and greater per-
ceived risk of marijuana were associated with lower
odds of supporting legalization. Similarly, politically
left of center or centrist political views and lifetime
marijuana use were associated with higher odds of
being unsure about legalization. Older age and greater
perceived risk of marijuana were associated with lower
odds of being unsure about legalization, relative to
opposing legalization. After controlling for other vari-
ables, education level was not a significant predictor of
attitudes towards legalization.
Notably, prior marijuana use and perceived risk of
marijuana were the strongest predictors of opinions
regarding legalization in the multivariate model.
Among those who had used marijuana in the
past year, 94.1% favored legalization, compared to
46.0% of those who had used prior to the
previous year, and 24.1% of those who had never used
marijuana. On a measure of perceived risk of marijuana
ranging from 1 to 4, those who opposed legalization
had the highest perceived risk (M = 3.4), followed by
those who were unsure about legalization (M =2.7), and
those who favored legalization (M = 1.9).
Discussion
As marijuana policy continues to evolve, an understand-
ing of attitudes toward legalization for recreational pur -
poses provides insights useful for political and prevention
efforts. It is particularly important to characterize those
who are undecided about marijuana legalization before

12. Table 1. Descriptive statistics.
Variable N % M SD
Age - - 45.37 13.39
Gender
Male 619 28.3 - -
Female 1571 71.7 - -
Children under 18 in Household 903 41.2 - -
Race
White 1986 90.7 - -
African American 97 4.4 - -
Other Race 107 4.9 - -
Education Level
High School Diploma or Less 459 21.0 - -
Bachelor’s Degree 892 40.7 - -
Graduate/Professional Degree 839 38.3 - -
Political Orientation
Left of Center 888 40.5 - -
Right of Center 536 24.5 - -
Center/Other 766 35.0 - -
Past Marijuana Use
Never used 781 35.7 - -
Lifetime Use 994 45.4 - -
Past Year Use 415 18.9 - -
Perceived Risk of Marijuana (scores range
from 1 to 4)
- - 2.59 0.94
Support Marijuana Legalization

13. Yes 1037 47.4 - -
No 911 41.6 - -
Unsure 242 11.1 - -
Table 2. Bivariate relationship between the predictors and
support, unsure or opposition to legalization of recreational
marijuana
use in Michigan.
Marijuana Legalization Marijuana Legalization
Variable Legal % Illegal % Unsure % Legal M(SD) MIllegal
(SD) Unsure M(SD) X2 F P value
Age - - - 43.5(13.6) 47.8(12.9) 44.4(13.2) - 27.06 < .001
Gender 38.14 - < .001
Male 57.7 34.6 7.8 - - -
Female 43.3 44.4 12.3 - - -
Children under 18 in Home 44.7 44.2 11.1 - - - 4.69 - .096
Race 3.21 - .524
White 47.4 41.6 11.0 - - -
African American 41.2 47.4 11.3 - - -
Other Race 52.3 35.5 12.1 - - -
Education Level 34.54 - < .001
HS Diploma or Less 54.9 33.3 11.8 - - -
Bachelor’s Degree 50.2 40.2 9.5 - - -
Graduate/Professional 40.2 47.6 12.3 - - -
Political Orientation 112.80 - < .001
Center 50.7 37.5 11.9 - - -
Right of Center 31.5 61.0 7.5 - - -
Left of Center 54.1 33.4 12.5 - - -
Marijuana Use 591.97 - < .001

14. Never 24.1 65.9 10.0 - - -
Lifetime Use 46.0 38.5 15.5 - - -
Past Year Use 94.5 3.1 2.4 - - -
Perceived Risk of Marijuana (range 1–4) - - - 1.9(0.69)
3.4(0.60) 2.7(0.58) - 1267.63 < .001
N = 2190
338 J. D. ELLIS ET AL.
they decide how they will vote, as prevention or advocacy
groups may benefit from giving particular attention to
these populations prior to elections. While previous
research on attitudes toward marijuana legalization (e.g.,
Cruz, Queirolo, and Boidi 2016; Galston and Dionne
2013) has yielded considerable insight on support for or
against marijuana legalization, less is known about those
who are undecided about marijuana legalization. Results
from the present study suggest that 47.4% of adults in
Michigan supported marijuana legalization and a sizable
minority were still undecided.
Findings from this study extend upon previous
research (Caulkins et al. 2012; Cruz, Queirolo, and Boidi
2016; Looby, Earleywine, and Gieringer 2007; Musgrave
and Wilcox 2013) that has shown conservative or liberal
political attitudes differentiate between those who support
and oppose marijuana legalization. Our findings suggest
that adults who are unsure about marijuana legalization
may be more similar, in terms of political orientation, to
those who support marijuana legalization, as being left of
center or center was associated with supporting or being

15. unsure about marijuana legalization. A notable minority
of politically conservative adults in our sample (31.5%)
supported legalization. This may reflect some ideological
and partisan crossover, where conservatives are increas-
ingly supporting legalization because they favor states’
rights and are suspicious of federal enforcement
(Galston and Dionne 2013).
Recent work found gender was significantly associated
with opinions regarding marijuana legalization, while
other demographic factors such as race, income, educa-
tion, and geography had only small relationships with
attitudes toward legalization (Galston and Dionne 2013).
The present study also suggested that women were more
likely than men to oppose legalization. The gender differ -
ences observed in the present study are notable in that
women, as a group, are more likely to vote left-of-center,
but are more aligned with political conservatives on this
issue (Galston and Dionne 2013). Interestingly, in the
present study, the bivariate results replicated previous
findings that higher education level is associated with
lower likelihood of favoring legalization, but this finding
disappeared when we controlled for other relevant factors.
Future research into demographic factors most strongly
associated with attitudes towards legalization, and poten-
tial reasons for these beliefs, may be beneficial.
The present study is only one of a few that has exam-
ined rates of supporting legalization among recent mar-
ijuana users. Those who were recent marijuana users
were more likely to support legalization compared to
those who had never used. It should also be noted that
recent marijuana users were not more likely to be unsure
than to be opposed to legalization, and rates of being
unsure about or opposing legalization were low among
past year users. This finding is in line with previous

16. studies (e.g., Cohn et al. 2017; Cruz, Queirolo, and
Boidi 2016; Williams, Van Ours, and Grossman 2011)
that have shown personal experiences with marijuana,
and one’s own use of marijuana, in particular (e.g., Cohn
et al. 2017; Cruz, Queirolo, and Boidi 2016; Trevino and
Richard 2002), is one of the strongest predictors of
supporting marijuana legalization.
Table 3. Multinomial logistic regression analysis predicting
atti-
tudes toward legalization of marijuana for recreational use in
Michigana.
Variable B SE Wald p-value OR 95%CI
Yes, Legal
Age −0.03 0.01 25.35 < .001 0.97 0.96–0.98
Female
Gender
−0.79 0.17 20.72 < .001 0.46 0.32–0.64
Has children −0.16 0.16 1.05 .305 0.85 0.63–1.16
Raceb
African
American
−0.23 0.35 0.43 .515 0.80 0.40–1.58
Other −0.01 0.34 0.001 .974 0.99 0.51–1.92
Political Orientationc
Left of
Center

17. 1.05 0.20 28.80 < .001 2.86 1.95–4.20
Center 0.63 0.20 10.14 .001 1.87 1.27–2.76
Education Leveld
Bachelor’s
Degree
0.10 0.21 0.24 .623 1.11 0.74–1.66
Graduate
Degree
0.03 0.21 0.02 .894 1.03 0.68–1.55
Marijuana usee
Past year 2.32 0.36 41.30 < .001 10.13 5.00–20.53
Lifetime 1.15 0.16 54.19 < .001 3.15 2.32–4.28
Perceived
risk
−2.85 0.13 486.56 < .001 0.06 0.05–0.08
Unsure
Age −0.03 0.01 14.43 < .001 0.98 0.96– 0.99
Female
Gender
−0.10 0.20 0.26 .610 0.90 0.61–1.34
Has children −0.14 0.17 0.72 .397 0.87 0.62–1.21
Raceb
African
American

18. −0.24 0.38 0.39 .531 0.79 0.37–1.66
Other −0.02 0.37 0.003 .954 0.98 0.48–2.01
Political Orientationc
Left of
Center
1.03 0.22 21.35 < .001 2.81 1.81–4.35
Center 0.86 0.22 14.99 < .001 2.37 1.53–3.67
Education Leveld
Bachelor’s
Degree
−0.38 0.22 2.92 .088 0.68 0.44–1.06
Graduate
Degree
−0.24 0.22 1.21 .271 0.79 0.51–1.21
Marijuana usee
Past year 0.46 0.48 0.92 .337 1.58 0.62–4.00
Lifetime 0.94 0.17 31.26 < .001 2.56 1.84–3.56
Perceived
risk
−1.51 0.13 138.37 < .001 0.22 0.17–0.28
Nagelkerke Pseudo Rb = 0.645
aNo, does not support legalization was the reference group for
the multi-

19. nomial logistic regression.
b Caucasian/White was used as the reference group for Race.
c Right of Center was the reference group for the Political
Orientation
variable.
d High School education was the reference group for the
Education Level
variable.
e Never Used Marijuana was the reference group for the
Marijuana Use
variable.
JOURNAL OF PSYCHOACTIVE DRUGS 339
Our findings regarding perceived risk associated
with marijuana extend earlier research that has focused
on adolescent samples. Campbell, Twenge and Carter’s
(2017) analysis of twelfth-graders in the Monitoring the
Future dataset, for example, found perceptions of risk
and support for legalization appear in tandem, with
higher perceived risk linked to low support for legaliza-
tion and lower perceived risk linked to strong support
for legalization. The current findings suggest a similar
pattern for adults. Those who supported or were unsure
about marijuana legalization had lower levels of per-
ceived risk compared to those who were opposed to
legalization. As perceived risk associated with mari-
juana use declines (Okaneku et al. 2015), findings on
personal experiences and risk perception may have
implications for the messaging of marijuana preven-
tion. Prevention messages that are designed to increase

20. risk perception may help to reduce marijuana use
among some, but also could potentially backfire for
those who perceive marijuana use to be benign.
The present study brings needed attention to people
who are undecided about marijuana legalization. Future
research may also benefit from examining what might
change decisions for individuals who have already formed
an opinion about marijuana legalization. Looby,
Earleywine, and Gieringer (2007), for example, found
that adults were more likely to support legalization if
a reliable roadside test could be administered.
Additional research is needed on how state regulations
for marijuana, including tax rates or limitations on who
may grow and distribute marijuana, may shape voting.
Regulations vary considerably from state to state and
evidence suggests they have already played a part in recent
elections. Legalization initiative that failed to pass, for
example, included a limit of 10 facilities given exclusive
commercial rights to grow marijuana in that state. This
regulation divided those who advocated for marijuana
legalization and is likely one of the reasons the initiative
failed (Graham 2015).
Additional research on the reasons people support,
oppose or are unsure about legalization is also
needed as attitudes toward marijuana continue to
shift (Kilmer and MacCoun 2017; Resko et al.
2019). Many people who support marijuana legaliza-
tion do so despite recognition of potential negative
consequences (Resko et al. 2019). As more states
move to legalize recreational marijuana, understand-
ing the influence of marijuana policy changes on
public attitudes is increasingly important. Some indi-
viduals may consider marijuana legalization as
a governmental endorsement that marijuana is safe

21. for recreational use (Moreno et al. 2016). Prevention
and education efforts may be needed to inform the
public that state-level marijuana legalization does not
imply governmental endorsement, nor does it suggest
that marijuana products have been deemed safe
(Moreno et al. 2016).
The results of this study should be considered in the
context of their limitations. First, the study was cross-
sectional. Given the ever-changing nature of public
opinion on marijuana (Kilmer and MacCoun 2017),
future studies may benefit from conducting longitudi-
nal analyses examining how attitudes toward legaliza-
tion change with time, and particularly whether these
attitudes change after legalization. The Michigan
Prevention Association opposes marijuana legalization,
and prevention providers distributed the survey, which
may have resulted in a sample that over-represents
adults with lower levels of support for marijuana lega-
lization. Additionally, the sample was not representa-
tive of the state of Michigan as a whole, and a yielded a
disproportionately high rate of White and female
respondents. Recruitment techniques that would yield
more representative and diverse samples, or use of
existing national datasets, may be ideal in the future.
For example, future studies could consider analyzing
data from a nationally representative sample, such as
the General Social Survey. Additionally, future studies
may want to consider oversampling among historically
underrepresented groups to ensure adequate represen-
tation of perspectives of those groups who have not
been well represented (e.g., racial-ethnic minorities and
those who identify as transgender or non-binary).
Recruiting a diverse sample may be particularly impor-
tant, as criminalization of marijuana and of substance

22. use more broadly has disproportionately impacted low-
income people of color (Koch, Lee, and Lee, 2016).
While evidence of racial or ethnic differences in atti -
tudes toward legalization has been mixed (e.g., Cohn
et al. 2017), future studies may benefit from further
exploring the reasons why some minorities support
and some oppose marijuana legalization.
Despite these limitations, the present study high-
lights that a sizable minority of adults are still unde-
cided about legalization. In addition to replicating
previously observed differences between those who
support and who oppose legalization, the present
study suggests that individuals who are unsure about
legalization are more likely to be younger and politi -
cally left of center or center than those who are
opposed. Additionally, those who are unsure were
more likely to report lifetime marijuana use and lower
levels of perceived risk of marijuana than those who
were opposed. These findings have important implica-
tions for advocacy groups as well as prevention efforts
in the evolving political climate.
340 J. D. ELLIS ET AL.
Disclosure statement
Dr. Stella Resko worked with the Michigan Prevention
Association to design and distribute the survey described in
this study. She does not have a financial relationship with the
Michigan Prevention Association, and the Michigan
Prevention Association was not involved in the writing of
this manuscript.

23. Funding
This project was unfunded.
ORCID
Stella M. Resko http://orcid.org/0000-0002-3323-0190
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AbstractIntroductionMethodsSample and study
proceduresMeasuresMarijuana legalizationDemographic
variablesMarijuana usePerceived risk associated with
MarijuanaData analysisResultsDiscussionDisclosure
statementFundingReferences
REVIEW ARTICLE
Cannabis use among U.S. adolescents in the era of marijuana
legalization:
a review of changing use patterns, comorbidity, and health
correlates
Christopher J. Hammonda,b,c , Aldorian Chaneya,c, Brian
Hendricksona,c and Pravesh Sharmad
aDivision of Child & Adolescent Psychiatry, Johns Hopkins
University School of Medicine, Baltimore, MD, USA;

31. bBehavioral
Pharmacology Research Unit, Johns Hopkins University School
of Medicine, Baltimore, MD, USA; cDepartment of Psychiatry
and
Behavioral Sciences, Johns Hopkins University School of
Medicine, Baltimore, MD, USA; dDepartment of Psychiatry,
Mayo Clinic
Health System and University of Wisconsin-Eau Claire, Eau
Claire, WI, USA
ABSTRACT
Decriminalization, medicalization, and legalization of cannabis
use by a majority of U.S. states
over the past 25 years have dramatically shifted societal
perceptions and use patterns among
Americans. How marijuana policy changes have affected
population-wide health of U.S. youth
and what the downstream public health implications of
marijuana legalization are topics of sig-
nificant debate. Cannabis remains the most commonly used
federally illicit psychoactive drug by
U.S. adolescents and is the main drug for which U.S. youth
present for substance use treatment.
Converging evidence indicates that adolescent-onset cannabis
exposure is associated with short-
and possibly long-term impairments in cognition, worse
academic/vocational outcomes, and
increased prevalence of psychotic, mood, and addictive
disorders. Odds of negative develop-
mental outcomes are increased in youth with early-onset,
persistent, high frequency, and high-
potency D-9-THC cannabis use, suggesting dose-dependent
relationships. Cannabis use disor-
ders are treatable conditions with clear childhood antecedents
that respond to targeted preven-
tion and early intervention strategies. This review indicates that

32. marijuana policy changes have
had mixed effects on U.S. adolescent health including potential
benefits from decriminalization
and negative health outcomes evidenced by increases in
cannabis-related motor vehicle acci-
dents, emergency department visits, and hospitalizations.
Federal and state legislatures should
apply a public health framework and consider the possible
downstream effects of marijuana pol-
icy change on paediatric health.
ARTICLE HISTORY
Received 15 September 2019
Accepted 6 January 2020
KEYWORDS
Adolescents; cannabis;
marijuana; legalization;
psychiatric comorbidity;
health correlates
Introduction
Cannabis is a psychoactive drug derived from the
plant species cannabis sativa and cannabis indica. It
contains greater than 500 bioactive chemicals and
more than 80 unique phytocannabinoids that have
distinct and dose-dependent effects in humans,
including D-9-tetra-hydrocannabidol (D-9-THC), the
primary psychoactive constituent, and cannabidiol
(CBD) another major constituent of the plant believed
to have potential medical properties (NCCIH, 2018).
Cannabinoids such as D-9-THC and CBD act cen-
trally and peripherally at receptors that are part of an
endogenous brain system involved in development
and homeostasis called the endocannabinoid system.

33. Cannabis is used by an estimated 183 million individ-
uals worldwide (WHO, 2019). Use of cannabis is
increasing among individuals living in North
America, in part related to legalization, decriminaliza-
tion, and expansion of availability in United States
(U.S.) and Canadian markets (Findlaw, 2019; WHO,
2019). Within the U.S. specifically, dramatic shifts in
public policy have occurred over the past two deca-
des. In 1996 California became the first U.S. state to
approve legislation allowing for the medical use of
marijuana. Since that time 32 other states and the
District of Columbia have passed laws allowing for
legal use of marijuana for medical purposes and 11
states have passed laws allowing for recreational use
of marijuana (Findlaw, 2019). Accompanying these
policy shifts in the U.S. have been changes in public
opinion, perception regarding the harms of cannabis,
cannabis use patterns, and the prevalence of cannabis
use disorders (CUD) among U.S. adults (Cerda, Wall,
Keyes, Galea, & Hasin, 2012; Hasin et al., 2017).
Over this period, there has also been a significant
expansion in the number and type of cannabis prod-
ucts available for consumption (e.g. plant, oil, edibles,
concentrates) (Hopfer, 2014) and three-fold increase
CONTACT Christopher J. Hammond [email protected] Johns
Hopkins Bayview, 5500 Lombard Street, Baltimore, MD 21224,
USA
� 2020 Institute of Psychiatry and Johns Hopkins University
INTERNATIONAL REVIEW OF PSYCHIATRY
2020, VOL. 32, NO. 3, 221–234
https://doi.org/10.1080/09540261.2020.1713056

34. http://crossmark.crossref.org/dialog/?doi=10.1080/09540261.20
20.1713056&domain=pdf&date_stamp=2020-04-23
http://orcid.org/0000-0003-3540-8201
https://doi.org/10.1080/09540261.2020.1713056
http://www.tandfonline.com
in the average D-9-THC potency in cannabis products
(ElSohly et al., 2016). While cannabis use is perceived
by the average American to have few negative conse-
quences, there is increasing evidence for poorer men-
tal and physical health outcomes, including elevated
risk for serious psychiatric illness with chronic recre-
ational cannabis use, especially when high-potency
cannabis is used (Davis et al., 2016; Dutra, Parish,
Gourdet, Wylie, & Wiley, 2018). The risk for negative
health outcomes related to cannabis use are amplified
when use and progression to chronic use begin dur-
ing adolescence.
Given the dramatic shifts in marijuana legislation
that have occurred in the U.S. over the past 25 years,
it is more important than ever for clinicians and pol -
icy makers to be aware of the effects of adolescent
cannabis use on mental and physical health and to
understand potential down-stream consequences
related to these policy shifts on perceptions, use pat-
terns, and health outcomes of U.S. adolescents.
Knowledge about the impact of marijuana policy on
relevant health indicators in youth may inform cur-
rent and future public health efforts. In this article,
we provide a state of the science review on the effects
of adolescent-onset cannabis use on health and behav-
iour with a focus on cannabis use and CUDs among
U.S. adolescents in the current era of state-based
marijuana legalization. We discuss the epidemiology,

35. recent trends in use, and examine relationships
between adolescent cannabis use and developmental
outcomes. Using a public health framework, we
review marijuana-related legislation and public policy
changes in the U.S. and examine the implications,
positive and negative, for adolescent health outcomes.
Epidemiology and developmental trajectories
Prevalence and incidence of cannabis use among
U.S. youth
Cannabis is the most commonly used federally illicit
drug among U.S. adolescents and the most common
drug problem reported by U.S. teens presenting for
substance abuse treatment (SAMHSA, 2018, 2019).
Over 1.6 million individuals between the ages of 12
and 17 equating to 6.5% of the U.S. adolescent popu-
lation, and 7.6 million individuals between the ages of
18 and 25 equating to 22.5% of the U.S. young adult
population reported current use of cannabis
(SAMHSA, 2018). Among U.S. high school students,
nearly half of all 12th graders (44%), one third of
10th graders (33%) and one in seven 8th graders
(14%) reported lifetime cannabis use in 2018, with
22%, 17%, and 5.6% of U.S. 12th, 10th, and 8th graders
reporting past month use respectively (Johnston et al.,
2018). Daily cannabis use was reported by 5.8% of
12th graders, 3.4% of 10th graders and 0.7% of 8th
graders. Rates of current cannabis use amongst 12-to-
17 year-olds decreased between 2002 and 2009 and
have remained stable since 2015 (SAMHSA, 2018). In
contrast, rates of current cannabis use amongst young
adults have risen significantly since 2002 (SAMHSA,

36. 2018). At the time of this writing, prevalence rates of
cannabis use in 19–22 year old ‘college age’ young
adults have gradually increased since 2009 and are
approaching their highest levels in the past three dec-
ades (Michigan, 2018). Some subgroups have shown
larger changes in cannabis use compared to others.
For example, while daily cannabis use among college-
enrolled U.S. youth peaked at 5.9% in 2014 and has
plateaued since then, daily use has continued to rise
for non-college enrolled U.S. youth and, at 13.2%, is
currently at an all-time high in the past three decades
(Schulenberg et al., 2018). This gap continues to
widen and is worrisome given the negative health and
functioning impact of recreational cannabis use.
Regarding incidence of cannabis initiation: In 2017,
1.2 million adolescents ages 12-to-17 and 1.3 million
young adults ages 18-to-25 reported first time use of
cannabis in the past year (SAMHSA, 2018). Since
2002, the incidence of cannabis use among U.S. ado-
lescents has remained stable, but has increased among
young adults (SAMHSA, 2018). Among youth, the
prevalence of past year CUD reached a peak in the
early 2000s, declined between 2002–2013, and has
remained stable since 2014. In 2017, 2.2% of adoles-
cents ages 12-to-17 equating to over 0.5 million U.S.
adolescents and 5.2% of young adults ages 18-to-25
equating to 1.8 million U.S. young adults met DSM-5
criteria for CUD in the past year (SAMHSA, 2018).
The types of cannabis products and methods of
administration among U.S. youth have also changed
in the past 25 years. While combustible cannabis
products (e.g. joints, blunts, bongs, water pipes)
remain the most common method of use, youth have
expanded to other types of cannabis products and

37. ways of using (Hopfer, 2014; Johnston et al., 2018). In
fact, data suggests that most current adolescent can-
nabis users use multiple administration methods to
consume cannabis (Peters, Bae, Barrington-Trimis,
Jarvis, & Leventhal, 2018). A 2015 cross-sectional sur-
vey study of 3177 adolescents found that 21.3% and
10.5% of 10th graders in California have tried edible
and vaporized cannabis products respectively (Peters
et al., 2018). The use of ‘concentrates’ (i.e. dabs, wax,
222 C. J. HAMMOND ET AL.
budder, shatter), cannabinoid products with very high
D-9-THC concentrations, are also increasing in popu-
larity among U.S. youth (Sagar & Gruber, 2018;
Zhang, Zheng, Zeng, & Leischow, 2016).
With the increasing availability of portable elec-
tronic ‘vaporized’ nicotine and cannabis delivery sys-
tems in the U.S., vaping cannabis is becoming more
common among youth. National survey data suggest
that 10% of high school students have vaped cannabis
with 12% and 14% of U.S. 10th and 12th graders
reporting vaping cannabis in the past year (Johnston
et al., 2018; Kowitt et al., 2019). While vaping has
been promoted as a safer alternative to combustible
smoking of tobacco and cannabis products, there
have been recent reports of vaping-related acute lung
disease, seizures, and deaths in young people, includ-
ing those who vape cannabis (Schier, Meiman, &
Layden, 2019). In response to this, the CDC has
recently issued health warnings related to vaping
(CDC, 2019).

38. In summary, across national surveys, prevalence
and incidence of cannabis use among U.S. teens have
remained stable and among U.S. young adults have
increased over the past decade. During this period,
there have been changes in the type and method of
cannabis product used by U.S. youth. Many questions
remain. Why cannabis use and CUD have not
increased in adolescents as they have in adults is
unclear. Additionally, over the same time period that
cannabis use rates have remained unchanged, alcohol,
combustible tobacco products, and non-marijuana
illicit drug use among U.S. adolescents ages
12–17 years have all decreased and are at or near all-
time low use patterns since data were first collected
in the 1970s (Johnston et al., 2018; SAMHSA, 2018).
Whether this comparative stability is a result of
changing U.S. perceptions and policies related to can-
nabis is unclear.
Individual differences in vulnerability and
different developmental trajectories
Significant individual differences exist in the response
to cannabis during youth (Coffey, Carlin, Lynskey, Li,
& Patton, 2003). Not all youth who try cannabis
develop problems related to its use. Some young peo-
ple experiment with cannabis, use it sporadically for a
limited duration, and experience few negative conse-
quences. Others become chronic cannabis users whose
use persists throughout adolescence and young adult-
hood and contributes to long-term health problems
and impaired functioning. Several studies have
identified different trajectories of cannabis use from
adolescence into young adulthood including a persist-
ent/chronic high use trajectory (�5–10%), a chronic

39. occasional use trajectory (�5–10%), a sporadic/transi-
ent use trajectory (�35%), and a no/low use trajectory
(�45%) (Lee, Brook, Finch, & Brook, 2018; Swift,
Coffey, Carlin, Degenhardt, & Patton, 2008; Windle &
Wiesner, 2004). Relative to no/low use and sporadic/
transient use trajectory groups, individuals in the per-
sistent/chronic high cannabis use trajectory group
have increased psychiatric problems, delinquency, and
other drug use by young adulthood (Lee et al., 2018;
Swift et al., 2008; Windle & Wiesner, 2004).
Understanding the risk and protective factors related
to cannabis engagement trajectories and developing
risk calculators to identify youth who are at elevated
risk for developing persistent/chronic cannabis use
may improve the precision and cost-effectiveness of
targeted prevention efforts.
A widening treatment gap for adolescent
cannabis use
Most individuals who experience drug-related prob-
lems or who meet criteria for a SUD, including can-
nabis, never receive treatment. In 2017, while
1.1 million U.S. adolescents met criteria for a SUD,
fewer than one in 10 received substance abuse treat-
ment (SAMHSA, 2018). Emerging evidence suggests
that for cannabis, this treatment gap may be widening
during the era of marijuana legalization. National
data on treatment episodes for substance-related dis-
orders indicate that fewer individuals are seeking
treatment for cannabis use/CUD in recent years
(Sahlem, Tomko, Sherman, Gray, & McRae-Clark,
2018; SAMHSA, 2019). For example, data on national
admissions to substance abuse treatment from the
treatment episode dataset (TEDS) showed a decrease
in admissions to adolescent substance abuse treatment

40. among 12–17-year-olds in general, and a 48%
decrease in the total number of cannabis-related
admissions between 2005 and 2015 (SAMHSA, 2017).
The reduction in treatment seeking rates may be a
result of increased social acceptability of cannabis use,
a reduction of the perceived risk of cannabis use, or a
result of the limited effectiveness of current treat-
ments (Sahlem et al., 2018). If expansion of marijuana
legalization results in increased cannabis engagement
among U.S. youth, this widening treatment gap could
portend a future public health crisis. Educational
campaigns aimed at increasing public awareness about
the harms of cannabis use to adolescents, and
INTERNATIONAL REVIEW OF PSYCHIATRY 223
continued research funding aimed at enhancing can-
nabis cessation outcomes and implementing and dis-
seminating effective cannabis treatments nationally
are needed. As more states change their views on can-
nabis use and revise their laws related to marijuana,
public health educational initiatives will be increas-
ingly important.
Health outcomes related to adolescent
cannabis use
Association with cognitive outcomes
The cognition impairing effects of cannabinoids in
humans are well documented in the scientific literature
in both adults and adolescents (Gorey, Kuhns,
Smaragdi, Kroon, & Cousijn, 2019; Lisdahl, Wright,
Kirchner-Medina, Maple, & Shollenbarger, 2014).

41. Cannabis-related cognitive deficits may be both global
and domain specific and can be temporally framed as
acute/intoxication-, short-, and long-term effects. Acute
cannabis intoxication is associated with transient mood
alterations that may include euphoria, anxiety, or para-
noia, along with impairments in cognitive function
and sensory processing (Bloomfield et al., 2019;
Hunault et al., 2009). When not intoxicated, adolescent
cannabis users exhibit signs of cognitive impairments
when compared to matched controls in the domains of
attention, memory, executive function (including work-
ing memory and inhibition), visual processing, and
processing speed, along with decreased full-scale IQ
and verbal IQ (Dougherty et al., 2013; Gruber, Sagar,
Dahlgren, Racine, & Lukas, 2012; Jacobus, Bava,
Cohen-Zion, Mahmood, & Tapert, 2009). Many of the
domain-specific cognitive deficits improve with abstin-
ence, but some may persist beyond early abstinence
and represent long-term deficits (Hanson et al., 2010;
Medina et al., 2007; Meier et al., 2012; Volkow et al.,
2016). For example, a study by Hanson and colleagues
found that following 3 weeks of abstinence from canna-
bis that adolescent regular cannabis users showed
improvements in verbal memory and inhibition but
continued to exhibit impaired attention compared to
controls (Hanson et al., 2010). Studies of adolescents
with earlier, heavier, and more persistent cannabis use
patterns generally show larger effect sizes for cognitive
outcomes (Gorey et al., 2019; Gruber et al., 2012;
Meier et al., 2012; Pope et al., 2003). Some studies
indicate that long-term cognitive impairments occur
primarily in early adolescent-onset of cannabis users
(� age of 15 or 16), and that adult- or late adolescent-
onset of cannabis users do not exhibit the same risk
for long-term cognitive impairments (Fontes et al.,

42. 2011; Gruber et al., 2012; Pope et al., 2003). Studies
have also largely shown that adolescent-onset cannabis
exposure produces similar cognitive deficits for both
sexes (Levine, Clemenza, Rynn, & Lieberman, 2017;
Meier et al., 2012; Pope et al., 2003).
Whether the cognitive impairments related to ado-
lescent-onset cannabis exposure are permanent or
resolve with abstinence is unclear. Mixed findings
have been reported in the literature. A longitudinal
study by Meier et al. (2012) found that full-scale IQ
decrements related to adolescent cannabis exposure
persisted into adulthood for individuals who contin-
ued to use cannabis and did not fully remit in early
adolescent-onset users who abstained from cannabis
during adulthood (Meier et al., 2012). Analyses from
other longitudinal studies suggest that some cognitive
deficits including global FSIQ decrements remit with
cessation and that length of abstinence is associated
with greater cognitive recovery (Mokrysz et al., 2016;
Tait, Mackinnon, & Christensen, 2011). Twins studies
discordant for cannabis engagement during adoles-
cence have also reported mixed findings related to
whether cannabis-associated cognitive deficits remit
or persist with abstinence in adulthood after control-
ling for genetic and early-childhood vulnerability
(Jackson et al., 2016; Lyon, Bar, & Panizzon, 2004).
Association with psychiatric symptoms and
mental health outcomes
The associations between adolescent-onset cannabis
use, psychiatric symptoms, and mental health out-
comes are complex (Levine et al., 2017). Cannabis use
and CUD commonly co-occur with psychiatric disor-
ders in youth. Concurrent cannabis use and psychi-

43. atric symptoms may track together in adolescents
with studies suggesting parallel improvement in both
during successful treatment (Hser et al., 2017; Jacobus
et al., 2017; Moitra, Anderson, & Stein, 2016). Aside
from concurrent relationships, long-term associations
have been described in the literature. Longitudinal
studies generally show that adolescent-onset cannabis
exposure is associated in a dose-dependent way with
an increased prevalence of psychotic, mood and
addictive disorders and worse courses of these disor -
ders into adulthood (Levine et al., 2017).
Psychotic disorders
Among all cannabis-related mental health outcomes,
the evidence is strongest for a relationship between
adolescent-onset cannabis use and psychotic disorders
224 C. J. HAMMOND ET AL.
(D’souza et al., 2016; Moore et al., 2007). Adolescent-
onset cannabis use increases the likelihood of devel -
oping attenuated psychotic symptoms, psychotic like
experiences, and full psychotic disorders by young
adulthood (Fridberg, Vollmer, O’Donnell, & Skosnik,
2011; Hall & Degenhardt, 2008; Moore et al., 2007).
Furthermore, among youth with psychotic disorders,
cannabis use is associated with worse course and
prognosis including greater risk for relapse to psych-
osis, increased hospitalizations, and poorer medication
adherence (Miller et al., 2009; Schoeler et al., 2016).
In parallel with other developmental outcomes, dose-
response relationships exist between cannabis use and
psychosis with early-onset, high frequency (�weekly),

44. and high-potency (�10% D-9-THC) conveying
greater risk (Di Forti et al., 2014; Hall & Degenhardt,
2015). Additively, early-onset daily use of high-
potency cannabis starting before age 15 poses a five-
to six-fold greater risk for the development of a
psychotic disorder compared to non-use (Di Forti
et al., 2014). Different cannabis-psychosis relation-
ships exist along different time-scales (Wilkinson,
Radhakrishnan, & D’Souza, 2014). Acute cannabis
intoxication can produce transient psychotic symp-
toms that resolve spontaneously without intervention
in some youth. Cannabis use can also lead to a pro-
tracted psychotic symptom course including a transi-
ent persistent psychosis or cannabis-induced
psychosis, which lasts beyond the period of acute
intoxication (Wilkinson, Radhakrishnan, & D’Souza,
2014). Cannabis-induced psychotic disorders may be
a harbinger for long-term risk for chronic psychosis.
A recent longitudinal study from Scotland found that
50–75% of individuals who experienced a cannabis-
induced psychotic disorder went on to develop
schizophrenia or bipolar disorder within 15 years
(Alderson et al., 2017). The link between cannabis
and psychosis is greater in individuals with child mal -
treatment or genetic vulnerabilities (Wilkinson et al.,
2014). Some but not all of the risk for developing
psychosis in adolescent cannabis users is related to
pre-existing vulnerability to psychosis. For example,
while adolescent cannabis users with a family history
of psychosis in a first-degree relative have a higher
risk of developing psychosis, cannabis use still con-
veys increased risk in adolescent cannabis users with
no familial risk (D’souza et al., 2016).
Mood and anxiety disorders

45. Complex relationships exist between cannabis use and
mood and anxiety disorders. Many cannabis using
youth self-report using cannabis to ‘self-medicate’
depression and anxiety, and to reduce stress (Hyman
& Sinha, 2009). When adults are administered canna-
binoids in the laboratory, D-9-THC exerts a biphasic
dose-dependent acute effect on anxiety, with low-dose
D-9-THC preparations being anxiolytic and high-dose
D-9-THC preparations being anxiogenic (Bloomfield
et al., 2019). In direct contradiction to these short-
term effects, the majority of longitudinal studies show
the opposite association, whereby adolescent-onset
cannabis use is associated with increased likelihood
and poorer course of mood and anxiety disorders
during adolescence and into adulthood (Degenhardt,
Hall, & Lynskey, 2003; Levine et al., 2017; Moore
et al., 2007).
Adolescent-onset cannabis use has been linked to
adverse mood outcomes including increased depres-
sion and suicidality in both population-wide cross-
sectional studies and a number of large longitudinal
cohort studies (Degenhardt et al., 2003; Gobbi et al.,
2019; Horwood et al., 2012; Moore et al., 2007; Silins
et al., 2014). It is important to note that while numer-
ous studies have reported a positive association
between adolescent cannabis use and depression,
there are also studies that failed to find this associ -
ation (Scholes-Balog, Hemphill, Evans-Whipp,
Toumbourou, & Patton, 2016). Results from a recent
meta-analysis found that adolescent-onset cannabis
use is associated with a modest increase in the odds
of depression, suicidal ideations, and suicide attempts
in young adulthood (Gobbi et al., 2019). Earlier meta-
analyses have found evidence for a dose-dependent

46. increase in risk for depression from adolescent canna-
bis use (Lev-Ran et al., 2014) and an age of onset
effect whereby initiation of cannabis before age
17 years conveys greater risk (Moore et al., 2007).
Results from a large retrospective study involving
13,986 twins found that the monozygotic twin who
reported more frequent cannabis use had a two-fold
greater odds of depression and suicidal ideations
compared with their twin counterpart who used less
frequently (Agrawal et al., 2017). This study indicates
that the association between cannabis and depression
cannot be explained by common vulnerabilities alone.
Interestingly, in parallel with cognitive sequelae, most
studies have shown that adolescent-onset cannabis
exposure results in similar mood outcomes for both
males and females (Coffey & Patton, 2016;
Degenhardt et al., 2013; Horwood et al., 2012).
Cross-sectional and longitudinal studies show that
compared to controls adolescent and young adult
cannabis users have increased anxiety, anxiety
INTERNATIONAL REVIEW OF PSYCHIATRY 225
sensitivity, and panic attacks, and increased rates of
co-occurring anxiety disorders including social anx-
iety disorder, panic disorder, and post-traumatic stress
disorders (PTSD) (Buckner et al., 2017; Cornelius
et al., 2010; Zvolensky et al., 2006). A recent meta-
analysis in adults suggests a modest relationship
between cannabis use and anxiety (Kedzior & Laeber,
2014). Findings regarding the directionality of these
associations are mixed. Adverse childhood experiences
and chronic stress generally precede the onset of can-

47. nabis use and increase the risk for early-onset canna-
bis use and progression to CUD by young adulthood
(Buckner et al., 2012; Hyman & Sinha, 2009). Some
longitudinal studies have shown a long-term relation-
ship between adolescent-cannabis use and increased
risk for anxiety disorders in adulthood (Degenhardt
et al., 2013; Fergusson & Horwood, 1997), while
others have shown no association (Buckner et al.,
2012) or the inverse association (Buckner et al.,
2008). Adolescent cannabis use and CUDs have been
prospectively associated with increased odds for panic
attacks and disorders, but some of the variances in
this relationship may be related to co-occurring
tobacco use (Zvolensky et al., 2008). More recently, a
2019 meta-analysis of longitudinal studies failed to
find an association between adolescent cannabis use
and later anxiety disorders (Gobbi et al., 2019).
Future research is needed in this area, especially given
that many states have added anxiety disorders and
PTSD as ‘indicated conditions’ for medical marijuana
(Mitchell, 2019).
Addictive disorders
As with cognitive, mood, and psychotic outcomes,
adolescent cannabis use is also associated with
increased risk for developing addictive disorders in
adulthood to cannabis and other drugs. Both cross-
sectional and longitudinal studies have shown a sig-
nificant relationship between early-onset cannabis
exposure and a greater likelihood of developing an
addictive disorder (Coffey & Patton, 2016; Fergusson,
Boden, & Horwood, 2015; Nocon, Wittchen, Pfister,
Zimmermann, & Lieb, 2006; E. Silins et al., 2017;
Swift et al., 2008; Swift et al., 2012). Drug engagement
typically follow a general sequence from ‘lite’ drugs

48. such as alcohol, tobacco, and cannabis to ‘heavier’
illicit drugs including opioids, stimulants. Much
debate has been made about the ‘gateway’ hypothesis,
and reverse gateways going from cannabis to tobacco
use have also been described (Patton, Coffey, Carlin,
Sawyer, & Lynskey, 2005). While part of the variance
in association between early-onset cannabis use and
escalation to other drugs can be explained by the
common liability hypothesis, there is also evidence
suggesting that cannabis’s effects on the developing
brain may also play a role (Hall & Degenhardt, 2015).
In animal models, adolescent-onset cannabinoid
exposure sensitizes striatal dopamine systems and
increases self-administration of opioids and stimulants
in adulthood (Pistis et al., 2004; Renard et al., 2016).
Some studies also suggest unique cannabis-opioid
associations whereby cannabis, more so than other
drugs, increases the risk for progression to opioid
misuse (Kaminer, 2017; Olfson, Wall, Liu, &
Blanco, 2018).
Summary of health outcome findings
In summary, current evidence indicates that adoles-
cent-cannabis exposure is associated with a number of
negative life outcomes including impairments in cogni-
tion and increased prevalence and worse course of
psychotic, mood, and addictive disorders. These associ -
ations are stronger in adolescents with earlier age of
onset, frequent and heavy use, and high-potency can-
nabis use, which is worrisome given the rising potency
and availability of cannabis throughout the U.S. As
findings are associative, causality cannot be deter-
mined. Next-level studies should aim to characterize
associations between adolescent-onset cannabis expos-

49. ure and health outcomes across different time scales
and at different levels of analysis (i.e. genomics, brain
circuits, behaviour, self-report). Future research should
incorporate cross-translational approaches; such as,
combining animal models, which have hinted at a
causal association, with longitudinal human studies
that assess both genetic and environmental factors and
include non-invasive brain imaging and deep behav-
ioural phenotyping as is being done in the Adolescent
Brain Cognitive Development (ABCD) study, a large
longitudinal study following 10,000U.S. preadolescents
over a 10-year period (Jernigan, Brown, & ABCD
Consortium Coordinators, 2018).
Marijuana legalization and its impact on
adolescent cannabis use
Changes in marijuana legislation in the U.S
Despite mass expansion of state-level marijuana legal-
ization in the U.S., the federal government has not
taken major legislative action related to marijuana in
the past two decades. Under current federal laws in the
U.S., cannabis possession and use are still considered
226 C. J. HAMMOND ET AL.
illegal and can be subject to federal prosecution
(Findlaw, 2019). Cannabis also remains classified as a
Schedule I substance by the U.S. Drug Enforcement
Agency (DEA), limiting its access for study by scientists
(DEA, 2019). The incongruence between federal and
state marijuana laws in the U.S. has resulted in confu-
sion, limited or delayed implementation of state laws,

50. and created complicated financing operations and state-
to-state legal implications for commerce (Findlaw,
2019; Vandrey, 2018). While the federal government
has been noncommittal regarding reclassifying canna-
bis, a majority of states within the U.S. have now
passed laws to legalize marijuana, in some form or
other, for medical and recreational use, as well as to
decriminalize possession of cannabis (Governing, 2019).
Medical and recreational marijuana in the U.S
Ongoing public advocacy related to marijuana use for
medicinal purposes, termed medical marijuana, con-
tinues to be a major reason for promotion of mari-
juana legalization initiatives (Pacula & Smart, 2017;
Vandrey, 2018). Cannabinoids have shown early
promise as novel treatments for a number of medical
conditions in early preclinical studies (Whiting et al.,
2015). For most of these conditions though, follow up
with controlled studies in humans have yet to confirm
these benefits. The use of marijuana as treatment for
medical conditions is complicated. Marijuana contains
multiple bioactive molecules including D-9-THC and
CBD, which have distinct and dose-dependent effects
in humans (NCCIH, 2018). Medical marijuana laws
vary widely by state and, in many states, marijuana
products are not consistently standardized in dose,
potency, or chemical constituency (Pacula & Smart,
2017; Vandrey et al., 2015). This is problematic if spe-
cific cannabinoids need to be used at specific doses to
be effective. While some states have set regulations
requiring quality control and labelling of dispensary-
sold medical marijuana preparations, it is unclear
how reliable these labels are. A recent study by
Vandrey and colleagues found that dispensary-
sourced marijuana edibles from multiple states had

51. poor accuracy of labelled doses (Vandrey et al., 2015).
Further complicating the application of medical mari-
juana are the issues of minimal physician documenta-
tion and supervision, which varies widely from state-
to-state (NCSL, 2019; Pacula & Smart, 2017). Despite
the limitations described above, medical marijuana
has been shown to be useful in adults for the treat-
ment of certain medical conditions including nausea,
vomiting, cachexia secondary to HIV/AIDs or cancer,
neuropathic pain, multiple sclerosis, and some forms
of epilepsy (NIDA, 2019; Whiting et al., 2015).
Beyond these conditions though, state legislatures
have approved medical marijuana for the treatment of
multiple other ‘indicated’ conditions (e.g. PTSD and
more recently Autism) based upon limited scientific
evidence in humans (Mitchell, 2019).
The use of medical marijuana for treatment of
childhood-onset medical conditions is controversial.
In states with medical marijuana legislation cannabis
is being prescribed to youth as a treatment for
ADHD, Autism, anxiety disorders, and bipolar dis-
order without any scientific evidence to support this
practice (Jaffe & Klein, 2010; Mitchell, 2019). Many
adolescents have obtained medical marijuana with
parents’ written permission (Ammerman, Ryan,
Adelman, Committee on Substance Abuse, & the
Committee on Adolescence, 2015). Young people who
use medical marijuana are more likely to have used
cannabis regularly between ages 13-19 years, and may
experience poorer developmental outcomes than
youth who use conventional medical treatments
(Tucker et al., 2019). To date, the only childhood
onset medical conditions that medical marijuana has
demonstrated preliminary efficacy in human studies

52. for are Lennox-Gastaut syndrome and Dravet syn-
drome, two rare childhood-onset seizure disorders (�
0.006% of U.S. population) (Volkow et al., 2016).
More research is clearly needed to determine both
potential benefits and harm or side effects from med-
ical marijuana use, and if there is any role for the use
of medical marijuana in childhood-onset medical con-
ditions and psychiatric conditions. For conditions
with a strong evidence base, comparative effectiveness
studies are needed to determine how marijuana may
be used in relation to FDA-approved medications.
Additional research is also needed to clarify the role
of medical marijuana in standard medical practice.
Overall, marijuana legislation has many moving parts,
which continually need to be examined as more states
legalize cannabis in various capacities. With all the
various forms of cannabis products, more studies are
needed to clarify how individuals uniquely utilize and
respond to different formulations (Hopfer, 2014).
Impact of marijuana legalization on youth
States that have legalized medical and recreational use
of cannabis continue to spark many discussions, par-
ticularly about the impact it may have on adolescent
health. Concerns have been raised that marijuana
laws have not taken into consideration the societal
INTERNATIONAL REVIEW OF PSYCHIATRY 227
and long-term public health impact legalization of
recreational and medical cannabis use will have on
communities. Alterations in perception of the harmful

53. effects of cannabis; unregulated commercialization of
cannabis products geared towards adolescents; and
decreased treatment utilization for excessive con-
sumption of cannabis are societal and public health
concerns that have been raised related to marijuana
legalization (Davis et al., 2016; Hall & Lynskey, 2016;
Wang, 2017).
An important caveat when considering the public
health outcomes related to marijuana legislation is
decriminalization and the potential for positive out-
comes in youth because of reduced juvenile justice
involvement. The illegality of marijuana has resulted
in the incarceration of hundreds of thousands of ado-
lescents, with overrepresentation of minority youth
(Ammerman et al., 2015). A criminal record can have
lifelong negative effects on an adolescent who other-
wise had no criminal justice history. These effects can
include ineligibility for college loans, housing, finan-
cial aid and certain kinds of jobs (Firth, Maher,
Dilley, Darnell, & Lovrich, 2019). Despite cannabis
being considered illegal for any use under federal law,
certain states have passed laws reducing penalties for
cannabis offences. Rather than criminal prosecution
or threat of arrest (Findlaw, 2019), civil penalties,
with the lowest misdemeanour, including no possibil-
ity for jail time have been created for individuals
caught with small, personal amounts of cannabis
(NCSL, 2019). Of note, while cannabis possession and
use remains federally illegal, the Justice Department
has not enforced federal law in states that have legal-
ized cannabis, under the guidance of the Cole
Memorandum that was adopted in August 2013
(DAG, 2013). However, this Memorandum has been
rescinded in January 2018, granting U.S. Attorneys
greater authority to enforce federal law (DAG, 2013,

54. 2018). It is the hope that decriminalization of mari-
juana will positively impact youth and minority com-
munities, resulting in lower utilization of the criminal
justice system, overall diminished incarceration rates,
and potentially decreased rates of disproportionally
incarcerated minority youth (ACLU, 2019).
Regarding the impact of changes in marijuana
legislation on beliefs, behaviours, and health outcomes
in U.S. youth, the results to date have been mixed
and difficult to interpret. Adolescents living in states
that have passed marijuana legislation report that can-
nabis is more easily accessible (Harpin, Brooks-
Russell, Ma, James, & Levinson, 2018). Over the past
two decades during which time most marijuana
legislation has passed, the perception that cannabis is
harmful has decreased dramatically and is near all-time
low levels among U.S. adolescents and young adults
nationally, regardless of state of residence (Keyes et al.,
2016; Miech, Johnston, & O’Malley, 2017). This is wor-
risome given the historic data showing that increased
use typically follows a reduction in perception of harm
for psychoactive drugs. The impact of marijuana legis-
lation on cannabis engagement patterns in adolescents
stratified by state of residence show minimal impact.
For example, numerous studies have shown that legal-
ization of medical marijuana has not led to an increase
in recreational use by adolescents (Ammerman et al.,
2015). However, states that have legalized marijuana
already had relatively higher rates of adolescent canna-
bis use before legalization occurred (Ammerman et al.,
2015). Additionally, with the legalization of marijuana
other deleterious effects from cannabis use have
increased in states with marijuana legislation including:
increased motor vehicle accidents and fatalities second-

55. ary to cannabis use; accidental overdoses of cannabis
by young children and pets; and increased emergency
department visits and hospitalizations as a result of
higher-potency cannabis use leading to psychosis,
depression and anxiety (Committee on Substance
Abuse, & the Committee on Adolescence, 2015; Hall
et al., 2018; Hopfer, 2014; Sevigny, 2018; Tefft, Arnold,
& Grabowski, 2016; Wang, 2017). Marijuana legaliza-
tion has also led to increased intention to use, diver-
sion from dispensaries, and recreational use of medical
marijuana by U.S. adolescents, including those enrolled
in substance abuse treatment (Boyd, Veliz, & McCabe,
2015; Harpin et al., 2018; Salomonsen-Sautel, Sakai,
Thurstone, Corley, & Hopfer, 2012). Furthermore,
legalization impacts the likelihood, and age at which,
youth use non-combustible cannabis methods such as
vaping and edible cannabis (Borodovsky et al., 2017).
Most published studies in this area have come from
ecological state-level analyses comparing population-
wide rates of use, beliefs, and negative outcomes
between adolescents residing in states that have and
have not passed marijuana related legislation. These
ecological studies are highly limited in their interpret-
ability and causal associations cannot be drawn from
them (McCarty, 2018). Future studies, examining dif-
ferences at the individual person-level are
greatly needed.
Conclusions
Over the past 25 years changing marijuana policies
have contributed to reductions in public perception of
228 C. J. HAMMOND ET AL.

56. harm, increased accessibility, and shifts in types and
modes of cannabis use among U.S. youth, but has not
resulted in increased use to date as feared by many
opponents of marijuana legalization. Still, given the
increased rates of cannabis use and related disorders
among U.S. adults (including parents) and growing
evidence that adolescent-onset cannabis use is associ-
ated with multiple negative health outcomes, children
and adolescents clearly represent a high-risk group.
Adolescent cannabis use, especially early-onset,
chronic, high frequency, and high-potency cannabis
use is associated with impairments in cognitive func-
tion; increased prevalence of mood, psychotic, and
addictive disorders; and poorer academic/vocational
outcomes. While some of the variances in these out-
comes can be attributed to socioeconomic status, IQ,
and mental health conditions that predate cannabis
initiation, many studies have identified significant
effects of adolescent-onset cannabis use even after
controlling for these variables suggesting that canna-
bis use itself may play a central role. Future research
is needed to determine whether this represents causal-
ity and to clarify whether direct or indirect pathways
exist. Identifying youth at elevated risk for initiating
cannabis early and for developing chronic high fre-
quency cannabis use and CUD is highly important.
Risk and prognostic factors emerging during child-
hood and adolescence can provide a roadmap for tar-
geted prevention and early intervention strategies that
are part of a larger continuum of treatment for CUD.
In addition to clarifying potential medical benefits,
future cannabis research efforts should also focus on
prevention and early intervention for cannabis use
and on clarifying individual differences in vulnerabil-
ity to developing CUD.

57. With significant marijuana legalization lobbyist
efforts and changing public perception regarding
marijuana amongst Americans, marijuana legalization
policies are poised to continue in the U.S. As U.S.
marijuana legalization policy initiatives move forward,
state legislatures should rely more on scientific evi-
dence from high quality replicated studies in humans
and less on preclinical studies, anecdotal reports, and
public opinion in developing future legislation.
Elected officials should be transparent about potential
conflicts of interest, such as marijuana lobbyist contri -
butions or their own personal investments in the
marijuana industry, as the presence of these conflicts
may influence or compromise professional judgment
and objectivity.
Marijuana legislation in the U.S. has resulted in a
number of downstream effects, some positive such as
decriminalization and reduced justice involvement,
and some negative such as increasing rates of CUDs
and emergency-related healthcare visits. Future mari-
juana legislation should find a balance between poten-
tial risks and benefits for individuals of all ages across
the lifespan, and not discount the risk for negative
consequences of policy change on youth.
Disclosure statement
Dr. Hammond receives grant support from the National
Institute on Drug Abuse/American Academy of Child &
Adolescent Psychiatry (NIDA/AACAP) career development
award (K12DA000357) and serves as a scientific advisor for
the National Courts and Science Institute. Dr. Sharma
receives grant support from an AACAP Pilot Research

58. Award for Junior Faculty. Drs. Chaney and Hendrickson
report no conflicts or financial disclosures.
Funding
Support for this study came from a National Institute on
Drug Abuse/American Academy of Child & Adolescent
Psychiatry (NIDA/AACAP) Physician Scholar in Substance
Abuse Research grant K12DA000357 (Hammond) and an
AACAP Pilot Research Award for Junior Faculty (Sharma).
ORCID
Christopher J. Hammond http://orcid.org/0000-0003-
3540-8201
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AbstractIntroductionEpidemiology and developmental
trajectoriesPrevalence and incidence of cannabis use among
U.S. youthIndividual differences in vulnerability and different
developmental trajectoriesA widening treatment gap for
adolescent cannabis useHealth outcomes related to adolescent
cannabis useAssociation with cognitive outcomesAssociation
with psychiatric symptoms and mental health
outcomesPsychotic disordersMood and anxiety
disordersAddictive disordersSummary of health outcome
findingsMarijuana legalization and its impact on adolescent
cannabis useChanges in marijuana legislation in the U.SMedical
and recreational marijuana in the U.SImpact of marijuana
legalization on youthConclusionsDisclosure
statementReferences