Retail Availability of Recreational Marijuana and Alcohol in Oregon Counties and Co-Use of Alcohol and Marijuana and Related Beliefs among Adolescents.

We investigated whether recreational marijuana legalization (RML) in Oregon in 2015 and recreational marijuana and alcohol retail outlet density levels in Oregon counties were associated with increased alcohol and marijuana co-use and beliefs supportive of alcohol and marijuana use among adolescents. We conducted secondary analyses of biennial data collected from 11th graders who participated in the Student Wellness Survey (SWS) in 36 Oregon counties from 2010 to 2018 ( = 71,870). Multi-level logistic regression analyses assessed changes in past-30-day co-use of alcohol and marijuana, and alcohol- and marijuana-related beliefs after RML in counties with low, medium, and high densities of licensed recreational marijuana and alcohol retail outlets. We used post-RML 2016 and 2018 SWS data to examine whether beliefs accounted for any relationship of recreational marijuana and alcohol outlet density with alcohol and marijuana co-use. We found a significant post-RML increase in past-30-day alcohol and marijuana co-use in 2016 in counties with the highest density of recreational marijuana and alcohol retail outlets. There were significant post-RML increases in perceived risk and parent approval of alcohol and marijuana use. Analyses with 2016 and 2018 SWS data indicated that the relationship between level of recreational marijuana and alcohol retail outlet density and past-30-day alcohol and marijuana co-use was accounted for beliefs about marijuana and alcohol availability, approval by parents, and risk. RML and greater retail availability of recreational marijuana and alcohol were positively associated with alcohol and marijuana co-use among adolescents, and with beliefs favorable to alcohol and marijuana use.