Systematic Review and Meta-Analysis: Medical and Recreational Cannabis Laws and Cannabis Use Among Youth in the United States

Objective Dramatic changes in state-level cannabis laws (CL) over the past 25 years have shifted societal beliefs throughout the US with unknown implications for youth. In the present study we conducted an updated systematic review and meta-analysis examining estimated effects of medical CL (MCL) and recreational CL (RCL) on past-month cannabis use among US youth. Method A systematic review was conducted following PRISMA guidelines followed by a subsequent meta-analysis investigating the associations between state-level cannabis laws (i.e., MCL vs. non-MCL, and RCL vs non-RCL) and past-month cannabis use prevalence among US adolescents and young adults. Supplemental analyses examined age-group effects and design-related factors. Results Our search identified 4604 citations, 34 and 30 of which were included in qualitative and quantitative analyses, respectively. Meta-analysis of MCL studies identified no significant association between MCL and change in past-month youth cannabis use (OR 0.981 [95% C.I. 0.960, 1.003]). Meta-analysis of RCL studies showed significantly increased odds of past-month cannabis use (OR 1.134 [95% C.I. 1.116-1.153]). Meta-analysis of more recent studies however showed a significantly increased odds of past-month cannabis use both amongst adolescents and young adults (OR 1.089[95% CI 1.015,1.169], and OR 1.221[95% CI 1.188,1.255], respectively). Conclusion Cannabis legalization has complex and heterogenous effects on youth use that may differ across law types. Our meta-analytic results showed modest positive effects of RCL on past-month cannabis use (more so in young adults than in adolescents) and minimal effects of MCL on these outcomes in US youth. Given the shift towards recreational legalization, additional focus on RCL effects is warranted.