Simultaneous alcohol and cannabis use is associated with daily consequences reflective of alcohol use disorder symptoms.

Alcohol use is common in the U.S., with 10.9 % of adults meeting criteria for alcohol use disorder (AUD) in 2023. Co-use of alcohol and cannabis is also widespread and is associated with increased alcohol-related harms. Few studies have examined how different co-use patterns, such as simultaneous (same day use with overlapping effects) versus concurrent (same day use without overlapping effects) use affect alcohol-related consequences, particularly those reflecting AUD symptoms. This study compares the associations between daily simultaneous, concurrent, and alcohol-only use patterns with the likelihood of endorsing alcohol consequences categorized as AUD symptoms. Participants (N = 116, 56 % female at birth, Mage=23.2) completed a 28-day ecological momentary assessment study, reporting daily alcohol and cannabis use and alcohol-related negative consequences. Analyses were preregistered. Consequences were categorized into four AUD categories based on DSM-5 criteria: impaired control, social impairment, risky use, and pharmacological effects. Multilevel binomial logistic regressions assessed the relationship between daily substance use patterns and each AUD consequence subtype. Compared to simultaneous use, concurrent use (i.e. using in the same day but without overlapping effects) was associated with a lower likelihood of endorsing (all p < 0.05): impaired control (OR=0.45), social impairment (OR=0.47), risky use (OR=0.41), and pharmacological effects (OR=0.36). No significant differences were found between simultaneous and alcohol-only days. Results underscore the relevance of the timing and pattern of alcohol and cannabis co-use in understanding alcohol-related problems. Further research is needed to explore the clinical implications of concurrent versus simultaneous use for AUD prevention and treatment.