Exposure to Opportunities for Use Moderates the Associations of Descriptive Norms and Perceived Risk with Alcohol and Cannabis Use and Simultaneous Use

BACKGROUND: We investigated whether exposures to opportunities for alcohol and cannabis use and simultaneous use moderate associations of descriptive norms and perceived risk with these behaviors such that substance use is lower for adolescents and young adults who report fewer opportunities regardless of their predispositions to engage in them. Method: Data were obtained using online surveys administered in 2023-24 to 1,014 adolescents and young adults (ages 15- to 20 years) in 40 California, USA, cities. They were asked how often they had an opportunity to engage in alcohol, cannabis, and simultaneous use in five different contexts in the past year, even if they chose not do so. They were also asked about past year frequency and typical quantity of alcohol and cannabis use and frequency of heavy drinking and simultaneous use of alcohol and cannabis. Additional questions asked about descriptive norms (friends' use), perceived risk for each substance use behavior, and demographic characteristics. Results: Multi-level mixed effects regression analyses accounting for nesting of participants within cities and for demographic characteristics showed that exposure to fewer opportunities for cannabis, alcohol, and simultaneous use was associated with reduced use. Consistent with our hypotheses, less use was observed among those who were more and less favorably predisposed to engage in these behaviors. Conclusion: These findings suggest that interventions limiting retail and social availability of alcohol and cannabis or constraining opportunities for use, can reduce alcohol and cannabis use and co-use among youth regardless of their predispositions to engage in these behaviors.