Comparing subjective effects and intoxication on simultaneous alcohol and cannabis use occasions relative to alcohol- or cannabis-only occasions.

Background: Simultaneous use of alcohol and cannabis-or use of both substances so effects overlap-is common among college-attending young adults and can heighten one's likelihood of experiencing substance-related harms in daily life. Limited ecological momentary assessment and daily diary work have examined the role of subjective intoxication and subjective effects when engaging in simultaneous relative to alcohol- or cannabis-only use, and studies have yielded mixed results. As such, subjective experiences serve as important internal cues for decision making; this study aimed to examine the level of subjective intoxication and effects across simultaneous, alcohol-only, and cannabis-only occasions.

Methods: Participants were 119 college students aged 18-25 who reported weekly simultaneous use at baseline. Participants enrolled in a 4-week ecological momentary assessment study with up to eight prompts per day collected on weekend days.

Results: Multilevel models revealed that relative to alcohol- and cannabis-only days, simultaneous use days were not significantly associated with subjective alcohol or cannabis intoxication, respectively. Peak levels of subjective alcohol effects were, however, significantly stronger during simultaneous use occasions relative to alcohol-only use occasions. Subjective cannabis effects were not significantly different between simultaneous and cannabis-only use days.

Conclusions: Study findings suggest that "adding" cannabis to an alcohol use occasion may bolster subjective effects such as feeling clumsy, confused, and having difficulty concentrating. Findings also highlight that subjective effects, rather than degree of impairment/intoxication, more strongly differentiates alcohol and simultaneous use occasions, and may serve as a useful momentary intervention target in future work.