Alcohol quantity mediates the association between daily alcohol and cannabis co-use and alcohol consequences

BACKGROUND: Alcohol and cannabis are commonly used substances for young adults, and person-level co-use (i.e., concurrent or simultaneous use of both) is associated with increased likelihood of experiencing positive and negative alcohol-related consequences. However, findings regarding within-person effects (i.e.,day-level) co-use on consequences are mixed, possibly due to inconsistency in including alcohol quantity (i.e., total number of standard drinks consumed) when examining the association between co-use and consequences. In the present study, we examined whether the number of drinks mediates the association between co-use and positive or negative alcohol consequences at the day level. METHODS: Data from morning reports in a 28-day field-based study of young adults reporting frequent past 60-day alcohol and cannabis use (N = 115) were used to test multilevel mediation models. RESULTS: We found significant mediation for both positive and negative alcohol consequences; consuming more alcoholic drinks on co-use days, relative to alcohol-only days, was associated with a higher likelihood of experiencing negative consequences and a lower likelihood of positive consequences. These results suggest that daily number of drinks is a significant driver of the relationship between co-use and alcohol-related consequences at the day-level. CONCLUSIONS: In the context of increased cannabis use among young adults, this finding provides critical information for prevention and intervention efforts aimed at reducing the alcohol-related consequences associated with co-use days. Overall, reducing total alcohol consumption remains a prominent harm-reduction strategy among this population.