The association between state cannabis policies and cannabis use among adults and youth, United States, 2002-2019.

Aims: To measure the association between state cannabis policies and use among adults and youth in the United States from 2002 to 2019, given rapid policy liberalization and complex state cannabis policy environments.

Design: Repeated cross-sectional time series analysis. Three sets of models assessed the linear association between the Cannabis Policy Scale (CPS), an aggregate measure of 17 state cannabis policy areas that weights each policy by its efficacy and implementation rating, and prevalence of cannabis use. The first included year and state fixed effects; the second added state-level controls; the third replaced state fixed effects with state random effects. Standard errors were clustered at the state level in all models.

Setting and participants: United States.

Measurements: Past-month prevalence of cannabis use is from the National Survey on Drug Use and Health Small Area Estimates, a nationally and state-representative cross-sectional survey of household population ages 12 and older for years 2002-2003 to 2018-2019. Exposure data include the CPS.

Findings: A 10 percentage-point increase in the CPS (i.e. greater cannabis policy restrictiveness) was associated with lower past-month use prevalence by 0.81 (95% confidence interval [CI] = -1.05 to -0.56) to 0.97 (95% CI = -1.19 to -0.75) percentage-points for the population ages 12 years and older. When models were stratified by age, a 10 percentage-point increase in the CPS was associated with a 0.87 (95% CI = -1.13 to -0.61) to 1.04 percentage-point (95% CI = -1.03 to -0.84) reduction in past-month use prevalence for adults ages 18 years and older, and a 0.17 (95% CI = -0.24 to -0.09) to 0.21 percentage-point (95% CI = -0.35 to -0.07) reduction for youth ages 12-17 years.

Conclusions: More restrictive US cannabis policies appear to be associated with reduced cannabis use for both adults and youth.