Daily Stress, Drinking Motives and Alcohol Co-Use with Other Drugs.

Background: Recent evidence indicates that alcohol and other substance co-use, compared to alcohol-only use, might be more closely associated with negative reinforcement processes, and thus more likely during periods of increased stress. The present study examined this possibility by using data from an intensive longitudinal (daily) study of college student drinkers ( N  = 1461, 54% women). We also examined individual differences in coping and enhancement drinking motives as predictors of alcohol and other substance co-use. Results: We used multilevel multinomial logistic regression to predict, relative to alcohol-only days, the likelihood of alcohol co-use with either cigarettes or marijuana, along with alcohol use with multiple substances and other substance-only use from daily interpersonal and academic stress, day-of-the-week, sex, and individual differences in coping and enhancement drinking motives. We found that, relative to alcohol-only, alcohol and marijuana co-use was more likely, and non-alcohol related substance use was less likely, on weekends. Alcohol and marijuana co-use was less likely, and other substance-only use was more likely, on days characterized by greater academic stress, whereas alcohol and cigarette co-use was more likely on days characterized by greater interpersonal stress. Individuals with higher levels of drinking to cope motivation were more likely to engage in alcohol and cigarette co-use, other substance-only use, and alcohol plus multiple substances, relative to alcohol-only. Individuals with higher levels of enhancement motives were more likely to engage in all types of alcohol and other substance co-use and other substance-only use relative to alcohol-only. Conclusions: Findings are discussed in terms of the complex nature of different patterns of co-use patterns when evaluating indicators of positive- and negative-reinforcement processes.