Heterogeneity of Within-Day Simultaneous Alcohol and Cannabis Use Behaviors Among Young Adults: A Multilevel Latent...

Simultaneous alcohol and cannabis use is prevalent among young adults and linked with heavy use and related harms. Days with simultaneous use have been linked with poorer proximal outcomes than days involving only alcohol/cannabis, but findings are mixed. Importantly, days with simultaneous use vary greatly with respect to level and timing of use, and other substance use. Thus, all simultaneous use days may not carry the same risks, partially explaining discrepancies. We aimed to characterize heterogeneity across simultaneous use days via an innovative statistical method applied to daily data - multilevel latent class analysis (MLCA) - and identify features of days most strongly linked to same-day harms and motives.

Participants were n=255 young adult college students (48% male) who completed ≤54 days of surveys on substance use behavior, yielding 1,527 person-days with simultaneous use.

MLCA identified four day-level latent classes of simultaneous use occasions: Alcohol-Focused (43% of days), Cannabis-Focused (35%), Heavy Use (14%), and Early-Day Use (8%). Same-day harms were more likely on Heavy Use days than other types of days, and day-level classes varied significantly with respect to three same-day motivations for simultaneous use: to be social, because it was offered, and to have fun.

Simultaneous alcohol and cannabis use days are highly varied. Heavy Use Days characterized by level of alcohol/cannabis use and engagement in other substance use were most strongly linked with harms, but timing of use in a day also distinguished patterns of use. Studies investigating the role of additional substances are warranted.