The Impact of Recreational Cannabis Markets on Cannabis Use Among Adolescents and Adults: A Synthetic Control Analysis.

Objective: To assess the longer-term impacts of recreational cannabis markets on cannabis use among adolescents and adults across five U.S. states. Method: Drawing on state-level data from the National Survey on Drug Use and Health, this study uses a novel method of causal inference called the synthetic control method with staggered treatment adoption to estimate the pooled effect of recreational markets on prevalence and initiation of use in Colorado, Washington, Oregon, Alaska, and Nevada. Three separate models were used for those 12-17, 18-25, and 26 and older. Pre-treatment state-level characteristics and trends in cannabis use were used to generate synthetic control weights. Confidence intervals were constructed using a leave-one-out jackknifing method. Results: Synthetic controls and treated states were similar in terms of sociodemographic characteristics, prevalence of other drug use, and trends in cannabis use prior to the implementation of recreational markets. The study results revealed moderate increases in prevalence and initiation of use among adolescents aged 12-17 (11% and 13%, respectively), and large increases in prevalence and initiation of use among young adults aged 18-25 (17% and 33%, respectively) and older adults aged 26 and older (33% and 82%, respectively) 2-4 years after dispensaries became operational. Conclusions: The findings of this study suggest recreational cannabis markets have increased prevalence and initiation of cannabis use among adolescents and adults. These increases may lead to adverse health outcomes depending on factors such as frequency of use and characteristics of users.