Recreational Marijuana Legalization and Co-use With Alcohol Among Adolescents

Introduction: Little is known about the possible impacts of recreational marijuana legalization on alcohol and marijuana co-use among underage youth. This study examines the association between recreational marijuana legalization in California in 2016 and alcohol and marijuana co-use among adolescents. Additional analyses investigate the associations between recreational marijuana legalization and co-use among past 30-day drinkers and marijuana users and the frequency of alcohol and marijuana use among co-users. Methods: This study used annual cross-sectional data from 7th, 9th, and 11th graders (N=3,319,329) who participated in the California Healthy Kids Survey from 2010-2011 to 2018-2019. Measures included past 30-day alcohol and marijuana use and student demographic characteristics, survey year, pre-post recreational marijuana legalization, and urbanicity. Multilevel regression analyses were conducted in 2021. Results: Recreational marijuana legalization was associated with greater odds of past 30-day alcohol and marijuana co-use in the total sample (OR=1.06, 95% CI=1.05, 1.07). Recreational marijuana legalization was more strongly associated with co-use among adolescents who reported past 30-day alcohol use (OR=1.58, 95% CI=1.52, 1.62) and heavy drinking (OR=1.25, 95% CI=1.21, 1.29) but was inversely related to co-use among past 30-day marijuana users (OR=0.76, 95% CI=0.74, 0.78). Among past 30-day co-users, there was a positive association with the frequency of marijuana use (beta=0.36, SE=0.07). Conclusions: Recreational marijuana legalization may increase the risk of alcohol and marijuana co-use among adolescents. Greater restrictions on the numbers of alcohol and marijuana retail outlets and hours of operation and advertising and higher taxes on alcohol and marijuana products may help reduce the availability of these substances to adolescents. (C) 2021 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.