• Priscila Dib Gonçalves, Natalie S Levy, Luis E Segura, Emilie Bruzelius, Anne E Boustead, Deborah S Hasin, Pia M Mauro, and Silvia S Martins.
• Department of Epidemiology, Columbia University Mailman School of Public Health, 722 West 168th St Room 509, New York, NY, 10032, USA.
• J Gen Intern Med. 2023 May 1; 38 (6): 149315001493-1500.

BackgroundSimultaneous cannabis/alcohol use, using both substances within a short time interval so that their effects overlap, has a greater risk of potential negative consequences than single-substance use and is more common in younger age. Relationships between recreational cannabis laws (RCLs) and changes in simultaneous cannabis/alcohol use prevalence remain untested.ObjectiveTo examine trends in simultaneous cannabis/alcohol use from 2008 to 2019, and investigate associations between implementation of RCLs (i.e., presence of active legal dispensaries or legal home cultivation) and simultaneous cannabis/alcohol use in the United States (U.S.).DesignRepeated cross-sectional samples from the 2008-2019 U.S. National Survey on Drug Use and Health (NSDUH).ParticipantsRespondents (51% female) aged 12 and older.InterventionsChanges in simultaneous cannabis/alcohol use before and after RCL implementation (controlling for medical cannabis law implementation) were compared in different age groups (12-20, 21-30, 31-40, 41-50, 51+), using adjusted multi-level logistic regression with state random intercepts and an RCL/age group interaction.MeasurementsSelf-reported simultaneous cannabis/alcohol use.ResultsFrom 2008 to 2019, the overall prevalence of simultaneous cannabis/alcohol use declined among those aged 12-20 but increased in adults aged 21+. Model-based simultaneous cannabis/alcohol use prevalence increased after RCL implementation among respondents aged 21-30 years (+1.2%; aOR= 1.15 [95%CI = 1.04-1.27]), 31-40 years (+1.0; 1.15 [1.04-1.27]), and 41-50 years (+1.75; 1.63 [1.34-1.98]), but not in individuals aged <21 or 51+ years.ConclusionsImplementation of recreational cannabis policies resulted in increased simultaneous use of cannabis and alcohol, supporting the complementarity hypothesis, but only among adults aged 21+. Efforts to minimize harms related to simultaneous cannabis/alcohol use are critical, especially in states with RCLs. Future studies should investigate cultural norms, perceived harm, and motives related to simultaneous use.© 2022. The Author(s), under exclusive licence to Society of General Internal Medicine.

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