Identifying classes of conjoint alcohol and marijuana use in entering freshmen

The current study identified classes of conjoint marijuana and alcohol use in entering college freshmen using latent profile analysis (N = 772; 53% male, 60% White; Mage = 18). Results yielded 4 distinct groups: Class 1 (moderate drinking with recent marijuana use: 22% of sample), Class 2 (moderate drinking with no recent marijuana use: 25%), Class 3 (light drinking with no recent marijuana use: 40%) and Class 4 (heavy drinking with recent marijuana use: 14%). Separate pairwise contrasts examined cross-class differences in demographics and drinking behaviors, comparing differences in drinking when current marijuana use was controlled (Class 1 vs. 4) and differences in marijuana use when drinking was held relatively constant (Class 1 vs. 2). Among moderate drinkers, recent marijuana users were more likely to drink more than intended, drink to get drunk, and had more problems (including higher rates of blackouts, physical injury, and DUI) relative to peers who refrained from marijuana. No cross-class differences were found for alcohol expectancies or behavioral motives. Findings from these analyses show the presence of distinct groups of conjoint users with different drinking behaviors and consequence profiles, and suggest that conjoint alcohol-marijuana use may be more problematic overall than single substance involvement and highlight the need for developing campus prevention and intervention programs that address the increased risk from polysubstance involvement.