Impact of state–level policy on adolescent marijuana use

Background: The state-level legalization of medical marijuana has raised concerns about increased accessibility and appeal of the drug to youth, who are most vulnerable to public messages about drug use and to the adverse consequences of marijuana. Objectives: To assess the impact of medical marijuana legalization in Rhode Island (RI) in 2006 by comparing trends in adolescent marijuana use between RI and Massachusetts (MA). Methods: We studied Youth Risk Behavioral Surveillance System (YRBSS) surveys from RI and MA between 1997 and 2009. Descriptive statistics (means, counts, percentages) were calculated. Chi-squared analysis was used to compare past-30 day marijuana use between states in each year. To evaluate the impact of the policy, we used a difference-in-difference analysis, which allows secular trends in drug use to be subtracted out, isolating the policy effect. A linear probability model was selected to simplify interpretation of the interaction term (state x policy). Covariates included demographics, alcohol use, and involvement in violence. Results: Among the 32,570 students, marijuana use was common across years (range 26% [95%CI, 23.5-28.4] to 34% [95%CI 28.9-39.6]). There were no statistically significant differences in marijuana use between states in any year. In the regression analysis, we did not find an increased probability of marijuana use related to the policy change (β=0.012 [SE 0.014], p=0.40). Conclusions: Our study did not find increases in adolescent marijuana use related to RI's 2006 legalization of medical marijuana. Additional research may follow future trends as medical marijuana in RI and other states becomes more widely utilized.