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How did the prevalence of adolescent marijuana use change in Washington and Colorado following legalization of recreational marijuana use?
In this difference-in-difference analysis of 253 902 adolescents in 47 states, marijuana use among eighth and 10th graders in Washington increased 2.0% and 4.1%, respectively, between 2010-2012 and 2013-2015; these trends were significantly different from trends in states that did not legalize marijuana. In Colorado, the prevalence of marijuana use prelegalization and postlegalization did not differ.
A cautious interpretation of the findings suggests investment in adolescent substance use prevention programs in additional states that may legalize recreational marijuana use.
Historical shifts are occurring in marijuana policy. The effect of legalizing marijuana for recreational use on rates of adolescent marijuana use is a topic of considerable debate.
To examine the association between the legalization of recreational marijuana use in Washington and Colorado in 2012 and the subsequent perceived harmfulness and use of marijuana by adolescents.
Design, Setting, and Participants
We used data of 253 902 students in eighth, 10th, and 12th grades from 2010 to 2015 from Monitoring the Future, a national, annual, cross-sectional survey of students in secondary schools in the contiguous United States. Difference-in-difference estimates compared changes in perceived harmfulness of marijuana use and in past-month marijuana use in Washington and Colorado prior to recreational marijuana legalization (2010-2012) with postlegalization (2013-2015) vs the contemporaneous trends in other states that did not legalize recreational marijuana use in this period.
Main Outcomes and Measures
Perceived harmfulness of marijuana use (great or moderate risk to health from smoking marijuana occasionally) and marijuana use (past 30 days).
Of the 253 902 participants, 120 590 of 245 065(49.2%) were male, and the mean (SD) age was 15.6 (1.7) years. In Washington, perceived harmfulness declined 14.2% and 16.1% among eighth and 10th graders, respectively, while marijuana use increased 2.0% and 4.1% from 2010-2012 to 2013-2015. In contrast, among states that did not legalize recreational marijuana use, perceived harmfulness decreased by 4.9% and 7.2% among eighth and 10th graders, respectively, and marijuana use decreased by 1.3% and 0.9% over the same period. Difference-in-difference estimates comparing Washington vs states that did not legalize recreational drug use indicated that these differences were significant for perceived harmfulness (eighth graders: % [SD], −9.3 [3.5]; P = .01; 10th graders: % [SD], −9.0 [3.8]; P = .02) and marijuana use (eighth graders: % [SD], 5.0 [1.9]; P = .03; 10th graders: % [SD], 3.2 [1.5]; P = .007). No significant differences were found in perceived harmfulness or marijuana use among 12th graders in Washington or for any of the 3 grades in Colorado.
Conclusions and Relevance
Among eighth and 10th graders in Washington, perceived harmfulness of marijuana use decreased and marijuana use increased following legalization of recreational marijuana use. In contrast, Colorado did not exhibit any differential change in perceived harmfulness or past-month adolescent marijuana use following legalization. A cautious interpretation of the findings suggests investment in evidence-based adolescent substance use prevention programs in any additional states that may legalize recreational marijuana use.
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Corresponding Author: Magdalena Cerdá, DrPH, MPH, Department of Emergency Medicine, University of California Davis School of Medicine, 2315 Stockton Blvd, Sacramento, CA 95817 (email@example.com).
Accepted for Publication: September 21, 2016.
Published Online: December 27, 2016. doi:10.1001/jamapediatrics.2016.3624
Author Contributions: Dr Wall and Ms Feng had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Cerdá, Wall, Schulenberg, O’Malley, Pacula, Galea, Hasin.
Acquisition, analysis, or interpretation of data: Cerdá, Wall, Feng, Keyes, Sarvet, Schulenberg, O’Malley, Pacula.
Drafting of the manuscript: Cerdá, Wall.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Wall, Feng, Keyes, Sarvet, Pacula.
Obtained funding: Schulenberg, O’Malley, Hasin.
Administrative, technical, or material support: Schulenberg, Pacula, Galea.
Study supervision: Cerdá, Schulenberg, Galea, Hasin.
Conflict of Interest Disclosures: None reported.
Funding/Support: The design, conduct, data collection, and management of the Monitoring The Future study was sponsored by the National Institute on Drug Abuse and the US National Institutes of Health and carried out by the Institute for Social Research at the University of Michigan, funded by grant R01DA001411. The analysis, interpretation of the data; and preparation, review, and approval of the manuscript was funded by grant R01DA034244 from the National Institute on Drug Abuse. Additional support is acknowledged from grants K01DA030449 and R01DA040924 from the National Institute on Drug Abuse (Dr Cerdá), grant K01AA021511 from the National Institute on Alcohol Abuse and Alcoholism (Dr Keyes), and the New York State Psychiatric Institute (Drs Hasin and Wall).
Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study.
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