Using Alcohol First Predicts Heavier Drinking on Simultaneous Alcohol and Cannabis Use Days, with no Evidence for...

Simultaneous alcohol and cannabis use is a common type of polysubstance use among young adults. Depending on the substance used first, the amount of alcohol consumed might vary. Coping or enhancement motives endorsed on simultaneous use days might also impact alcohol consumption differently. This study examined whether alcohol use differed on alcohol-only versus simultaneous use days, and whether using alcohol versus cannabis first on a simultaneous use day predicted heavier alcohol consumption. We also examined whether differences in alcohol consumption depended on daily levels of coping or enhancement motives.

Undergraduate students (n = 370; M_age=20.8; SD = 1.5) completed a 14-weekend daily diary study in Fall 2021. Surveys administered Friday to Sunday mornings measured alcohol use, cannabis use, their order of use, number of drinks consumed, and motives for simultaneous use. Analyses were restricted to alcohol-only and simultaneous use days (n = 2826/9017; 31.3%).

Multilevel models showed that students consumed more alcohol on simultaneous use days (M_drinks=5.08) than alcohol-only days (M_drinks=4.23). Students also consumed about 1.4 fewer drinks when cannabis was used first compared to when alcohol was used first on simultaneous use days. However, the effect of order of use on alcohol consumption did not depend on daily levels of coping or enhancement motives.

Using cannabis first on simultaneous use days was associated with less drinking, an effect not apparently linked to situational drinking motives. Contextual factors associated with cannabis use such as affect (e.g., negative or positive) and setting (e.g., alone or with others) may explain lighter drinking on cannabis-first simultaneous use days.