State marijuana and alcohol policies and co-use among adolescents

Introduction. Liberalization of marijuana laws raises concerns regarding greater availability, more favorable norms, and increased use by adolescents. Previous studies have examined associations of marijuana laws with marijuana use by youth with mixed results, but few studies have investigated the effects of marijuana and alcohol laws on marijuana and alcohol co-use. A study in Oregon found an increase in marijuana and alcohol co-use among adolescents after recreational marijuana legalization in 2015, particularly in counties with greater retail marijuana and alcohol availability. No studies, however, have investigated the combined effects of state marijuana and alcohol policies on co-use. Objective. The goal was to examine associations between variations of state-level marijuana and alcohol policies restrictiveness and marijuana and alcohol co-use among adolescents. We hypothesized that youth living in states with more liberal policies will have higher rates of marijuana and alcohol co-use and that marijuana and alcohol policies will interact such that co-use would be significantly higher when both were less restrictive. Method. We analyzed data from 13,702 students living in 25 states who participated in the 2019 Youth Risk Behavior Survey (YRBS). Students were asked about marijuana and alcohol use frequency in the past 30-days. Those who engaged in marijuana and alcohol use at least once in the past 30-days were classified as marijuana and alcohol co-users (1=yes, 0=no). We assessed the restrictiveness of state-level alcohol regulatory policy environments using the 2018 Alcohol Policy Scale (APS) and created an overall Marijuana Policy Score (MPS) for each state for 2018 with higher scores representing a more liberal marijuana policy environment. Policy domains in the MPS included recreational legalization (0=no, 4=yes), medical legalization (0=no, 1=CBD only, 2=no restriction), minimum legal age for medical marijuana use (0=21 years old, 2=18 years old), decriminalization (0=no, 2=yes), retail sales (0=no, 1=off-premise, 2=on/off-premise) and home deliveries (0=not allowed 1=with restrictions, 2=no restrictions). We performed multilevel mixed logistic regression analyses using Stata version 17, accounting for nesting of schools within states and students within schools. Covariates included age, sex, ethnicity, and race. Results. Less restrictive policy environments were associated with a greater likelihood of marijuana and alcohol co-use (MPS OR=1.50, 95% CI: 1.21, 1.87; APS OR=1.03, 95% CI: 1.01, 1.05). The interaction of the state marijuana and alcohol policies showed that the least restrictive combination of these policies was marginally associated with lower odds of marijuana and alcohol co-use (OR=.99, 95% CI: 0.99, 1.00), but this association was not substantively meaningful beyond the independent effects of the two policy measures. Conclusion. Our findings show that less restrictive state-level marijuana and alcohol policy environments, especially for marijuana policies, are associated with increased prevalence of marijuana and alcohol co-use among adolescents. These findings suggest that additional prevention efforts are needed as more states liberalize their marijuana laws. Future studies should consider other negative consequences associated with less restrictive policies and resulting from co-use, and changes in marijuana and alcohol co-use among adolescents over time.