Alcohol Use Motives and Cannabis Use among Young Adults: Between- and Within-Person Associations Based on Monthly Data from a Community Sample.

Objective: Alcohol use motives may characterize types of drinking that have unique associations with cannabis use and illuminate psychological processes underlying cannabis use. This study examined how alcohol use motives, both on average across two years and in a particular month, were associated with any and frequent cannabis use. Method: A young adult community sample (n = 486; 54% female, age 18-23 at enrollment) who used alcohol and cannabis in the year prior to study enrollment provided two years of monthly data. Multilevel logistic regression models predicting any and frequent (10+ occasions) past-month cannabis use estimated both between- and within-person effects of alcohol use motives, controlling for frequency of alcohol use and demographic covariates.
Results: Alcohol use frequency was positively associated with any cannabis use at the between- and within-person levels and frequent cannabis use at the within-person level. Across two years, individuals who had higher average coping drinking motives and lower average social and conformity drinking motives were more likely to use cannabis frequently. Further, between-person variation in social motives was negatively associated with any cannabis use. Within-person, months with greater enhancement and social motives were associated with higher probability of any cannabis use. Conclusions: Using alcohol for coping reasons, rather than other-focused social reasons, indicated greater risk for frequent cannabis use, although drinking for social and enhancement reasons in a particular month signaled slightly increased short-term probability of any cannabis use. Assessment of alcohol motives may help guide targeting and timing of prevention related to cannabis use.