How do cannabis laws impact teen cannabis use?

Anderson DM, Hansen B, Rees DI, Sabia JJ. Association of Marijuana Laws with Teen Marijuana Use: New Estimates from the Youth Risk Behavior Surveys. JAMA Pediatrics 2019;173(9):879-881 (Letter to the Editor)

Why was this study conducted?

The authors wanted to see whether the legalization of cannabis for adults (for recreational and/or medicinal uses) affects cannabis use by adolescents. To study this question, the authors analyzed data from the Youth Risk Behavior Survey from 1993 to 2017, a biennial survey of American high school students in grades 9 through 12. Data were analyzed at the state level so odds ratios could be calculated comparing states with legalized medical (n=27) or recreational (n=7) cannabis legislation to those with neither (n=20).

What does this study add?

In a model adjusting for state, year, and individual-level characteristics such as age, sex and grade, medical cannabis legislation had no statistically significant effect on cannabis use in the past 30 days or frequent use (i.e., at least 10 times in the past 30 days). However, legalization of recreational cannabis had a small but statistically significant negative impact on youth cannabis use (OR=0.92, 95% CI 0.87-0.96) and frequent use (OR=0.91, 95% CI 0.84-0.98). In other words, legalization was associated with a reduction in cannabis use.

Is there anything else I should know?

The surveys are cross-sectional and so could not follow changes in the behaviour of individual youth as state laws were changed. The authors did not speculate why legalizing recreational cannabis for adults was associated with a small but significant decrease in youth cannabis use. They comment that replacing black market sellers with licensed dispensaries that require proof of age may make it more difficult for youth to purchase cannabis.