A quasi-experimental evaluation of marijuana policies and youth marijuana use

ABSTRACT

Background: Marijuana use carries risks for adolescents’ well-being, making it essential to evaluate effects of recent marijuana policies.

Objectives: This study sought to delineate associations between state-level shifts in decriminalization and medical marijuana laws (MML) and adolescent marijuana use.

Methods: Using data on 861,082 adolescents (14 to 18+ years; 51% female) drawn from 1999 to 2015 state Youth Risk Behavior Surveys (YRBS), difference-in-differences models assessed how decriminalization and MML policy enactment were associated with adolescent marijuana use, controlling for tobacco and alcohol policy shifts, adolescent characteristics, and state and year trends.

Results: MML enactment was associated with small significant reductions (OR = 0.911, 95% CI [0.850, 0.975]) of 1.1 percentage points in current marijuana use, with larger significant declines for male, Black, and Hispanic (2.7–3.9 percentage points) adolescents. Effects of MML increased significantly with each year of exposure (OR = 0.980, 95% CI [0.968, 0.992]). In contrast, decriminalization was not associated with significant shifts in use for the sample as a whole, but predicted significant declines in marijuana use among 14-year olds and those of Hispanic and other ancestry (1.7–4.4 percentage points), and significant increases among white adolescents (1.6 percentage points). Neither policy was significantly associated with heavy marijuana use or the frequency of use, suggesting that heavy users may be impervious to such policy signals.

Conclusion: As the first study to concurrently assess unique effects of multiple marijuana policies, results assuage concerns over potential detrimental effects of more liberal marijuana policies on youth use.

KEYWORDS:

• Marijuana
• drug use
• policy
• adolescent risk behaviors
• cannabis

Acknowledgments

The study sponsors had no role in the study design; the collection, analysis, and interpretation of data; the writing of the report; or the decision to submit the manuscript for publication.

Conflicts of interest

None of the authors have any potential, perceived, or real conflicts of interest or financial conflicts.

Disclaimer

The results and conclusions reported are those of the researchers and not the Departments of Health of the states providing data.

List of Abbreviations

MML	=	medical marijuana laws
YRBS	=	youth risk behavior survey

Additional information

Funding

Research reported in this publication was supported by a Boston College Research Across Departments and Schools (RADS) grant to R.L.C.