Association Between Recreational Marijuana Legalization in the United States and Changes in Marijuana Use and Cannabis Use Disorder From 2008 to 2016

Magdalena Cerdá, DrPH; Christine Mauro, PhD; Ava Hamilton, BA; Natalie S. Levy, MPH;
Julián Santaella-Tenorio, DrPH; Deborah Hasin, PhD; Melanie M.Wall, PhD;
Katherine M. Keyes, PhD; Silvia S. Martins, MD, PhD

JAMA Psychiatry, 2019.

doi : 10.1001/jamapsychiatry.2019.3254

 

IMPORTANCE : Little is known about changes in marijuana use and cannabis use disorder (CUD) after recreational marijuana legalization (RML).

OBJECTIVES : To examine the associations between RML enactment and changes in marijuana use, frequent use, and CUD in the United States from 2008 to 2016.

DESIGN, SETTING, AND PARTICIPANTS : This survey study used repeated cross-sectional survey data from the National Survey on Drug Use and Health (2008-2016) conducted in the United States among participants in the age groups of 12 to 17, 18 to 25, and 26 years or older.

INTERVENTIONS : Multilevel logistic regression models were fit to obtain estimates of before-vs-after changes in marijuana use among respondents in states enacting RML compared to changes in other states.

MAIN OUTCOMES AND MEASURES : Self-reported past-month marijuana use, past-month frequent marijuana use, past-month frequent use among past-month users, past-year CUD, and past-year CUD among past-year users.

RESULTS : The study included 505 796 respondents consisting of 51.51%females and 77.24% participants 26 years or older. Among the total, 65.43%were white, 11.90% black, 15.36% Hispanic, and 7.31% of other race/ethnicity. Among respondents aged 12 to 17 years, past-year CUD increased from 2.18%to 2.72%after RML enactment, a 25%higher increase than that for the same age group in states that did not enact RML (odds ratio [OR], 1.25; 95%CI, 1.01-1.55). Among past-year marijuana users in this age group, CUD increased from 22.80% to 27.20% (OR, 1.27; 95%CI, 1.01-1.59). Unmeasured confounders would need to be more prevalent in RML states and increase the risk of cannabis use by 1.08 to 1.11 times to explain observed results, indicating results that are sensitive to omitted variables. No associations were found among the respondents aged 18 to 25 years. Among respondents 26 years or older, past-month marijuana use after RML enactment increased from 5.65%to 7.10% (OR, 1.28; 95%CI, 1.16-1.40), past-month frequent use from 2.13%to 2.62%(OR, 1.24; 95%CI, 1.08-1.41), and past-year CUD from 0.90% to 1.23%(OR, 1.36; 95%CI, 1.08-1.71); these results were more robust to unmeasured confounding. Among marijuana users in this age group, past-month frequent marijuana use and past-year CUD did not increase after RML enactment.

CONCLUSIONS AND RELEVANCE : This study’s findings suggest that although marijuana legalization advanced social justice goals, the small post-RML increase in risk for CUD among respondents aged 12 to 17 years and increased frequent use and CUD among adults 26 years or older in this study are a potential public health concern. To undertake prevention efforts, further studies are warranted to assess how these increases occur and to identify subpopulations that may be especially vulnerable.

Key Points

Question : How did marijuana use and cannabis use disorder change during 2008 to 2016 after the legalization of recreational marijuana in the United States?

Findings : In this multilevel, difference-in-difference survey study with 505 796 respondents comparing marijuana use before and after the legalization of recreational marijuana in the United States, the proportion of respondents aged 12 to 17 years reporting cannabis use disorder increased from 2.18%to 2.72%, while the proportion of respondents 26 years or older reporting frequent marijuana use increased from 2.13%to 2.62%and those with cannabis use disorder, from 0.90% to 1.23%.

Meaning : This study’s findings suggest that possible increases in the risk for cannabis use disorder among adolescent users and increases in frequent use and cannabis use disorder among adults after legalization of recreational marijuana use may raise public health concerns and warrant ongoing study.

 

Marijuana is one of theworld’s mostwidely used psychoactive substances. Approximately 183 million people, or 3.8%of theworld’s population, used marijuana in 2015.1 Although occasional marijuana use is not associated with substantial problems, long-term, heavy use is linked to psychological and physical health concerns,2-4 lower educational attainment,5 decline in social class, unemployment,6,7 and motor vehicle crashes.8,9

In the United States, 33 states and the District of Columbia have enacted medical marijuana legalization (MML), and 11 states and the District of Columbia have enacted recreational marijuana legalization (RML). Reducing racial/ethnic inequalities in marijuana-related arrests and convictions has been a keyaimof legalization.At thesametime, questions have arisen about the impactof legalizationonmarijuana use.10Prior studies did not find any association between MML and adolescent marijuana use11; however, they did find increases in adult past-month use and cannabis use disorder (CUD) after MML.12-19 Findings on MML may not apply to RML,20 because RML could have a broader impact through changes in pricing,21 access, acceptability,22,23 and advertising.

Little is known about the association of RML with marijuana use and howit differs fromthat ofMMLwith marijuana use. In school-based samples, one study found increased pastmonth adolescent use in Washington but not in Colorado after RML.24 Another study found increases in use among college students in Washington,25 while a third study found decreased marijuana use among adolescents.26 At the national level, the association of RML with marijuana use, frequent use, andCUDacross age groups remains unknown. Furthermore, whether RML leads to an expansion of the pool of new marijuana users or increases problematic use among existing marijuana users is unclear.

In this study,we addressed these gaps by comparing pastmonth marijuana use, frequent marijuana use, and CUD before and after RML enactment among adolescents, young adults, and adults, using data from 2008 to 2016. To distinguish the association of RML enactment with new marijuana users from that with problematic use among existing users,we examined changes in frequent marijuana use and CUD among the overall sample aswell as among users. States that did not enact RML, regardless of whether they had enacted MML, were included in the analyses to control for nationwide trends in marijuana use.

Methods

Data
The National Survey on Drug Use and Health (NSDUH) collects data on more than 17 500 adolescents (aged 12-17 years), 17 500young adults (aged 18-25 years), and 18800adults (aged ≥26 years) on a yearly basis.27 The NSDUH uses a 50-state designandhasanindependent multistage areaprobabilitysample for each state, which produces state-representative estimates. Upto 2013, equal sample sizes (33%)were collected for all the age groups. Since 2014, adults 26 years or older were oversampled (25% for youth aged 12-17 years, 25% for young adults aged 18-25 years, and50%for adults aged ≥26 years) to more accurately estimate drug use among the aging, drugusing population. This sample redesign did not change the prevalence estimates of outcome variables or the precision of the estimates between states that did and did not enact RML equally.

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