Understanding Heterogeneity Among Simultaneous Alcohol and Marijuana Users: Latent Classes Derived From Daily Diary Data

Objective: Simultaneous use of alcohol and marijuana (SAM) is common among U.S. college students, but little research has examined specific substance use behaviors during SAM use episodes. This study identified latent classes of SAM users based on their SAM, alcohol-only, and marijuana-only use episodes. Method: College student SAM users (N = 284; 50.7% female; M age = 19.8 years) completed up to five surveys each day across two 4-week bursts. Latent class analysis (LCA) was used to characterize SAM users based on seven latent class indicators of use behavior. Sex was examined in relation to latent class membership. Results: Five unique classes emerged: Frequent Marijuana-Focused SAM users (21%); Frequent Alcohol-Initiating SAM users (29%); Heavy-Drinking Infrequent SAM users (12%); Moderate SAM users (29%); and Light Infrequent SAM users (9%). These groups were differentiated primarily by their frequency of SAM use, form of marijuana, whether marijuana was used on non-SAM occasions, and whether consequences were experienced. Groups differed significantly by sex. Conclusions: College student SAM users are heterogeneous with respect not only to their degree of SAM use but also in their pattern of drinking, type of marijuana use, relative focus on alcohol versus marijuana, and risk of experiencing acute negative consequences. Describing this heterogeneity is an important step toward developing interventions for different types of users.