More Reasons, More Use and Problems? Examining the Influence of Number of Motives on Consumption and Consequences Across Alcohol-Only, Cannabis-Only, and Simultaneous-Use Days.

Objective Alcohol and cannabis use as well as their simultaneous use are common among U.S. college students. Reasons for use are proximal predictors of consumption and consequences. Little research has examined possible adverse effects of endorsing multiple motives on a given use day. We examined the effects of the number of motives on consumption and negative consequences for alcohol-only, cannabis-only, and simultaneous-use days. Method College students (N = 341; 53% women; mean age = 19.79 years) who reported past-month simultaneous alcohol and cannabis use completed 54 days of data collection. We used generalized linear mixed-effects models to examine the effects of endorsing multiple motives on consumption and consequences. Results Across models, endorsing more motives than typical on a given use day (within person) and more motives in general (between person) was related to greater alcohol and cannabis consumption. Endorsing more alcohol-only motives and cannabis-only motives than typical resulted in greater odds of experiencing a negative consequence when accounting for consumption. This within-person effect was not statistically significant for simultaneous-use motives/consequences. Endorsing a greater number of motives across the study (i.e., between person) was not significantly related to consequences beyond consumption. Conclusions Research has documented the robust effects of specific motives on substance use outcomes. Our novel findings extend this work by demonstrating the risks associated with endorsing multiple motives on a given use day. In addition to motive type, we recommend that the number of motives endorsed on a given day be considered as a potential risk factor to be targeted to reduce harms associated with substance use.