Using Cannabis and Alcohol Together Made People More Intoxicated and Predicted Riskier Use Later

Co-use of cannabis and alcohol was associated with greater momentary intoxication compared to either substance alone, and greater stimulation and bad effects compared to cannabis alone. Using both within 30 minutes produced the strongest effects. Individuals who became more intoxicated during co-use had greater risk of increasingly hazardous cannabis use at 6 and 12 months.

Longitudinal study of 155 young adults (mean age 21, 55.5% women) who co-used cannabis and alcohol. Ecological momentary assessment (EMA) over 21 days at baseline captured real-time co-use and subjective effects. Follow-up assessments at 6 and 12 months measured hazardous cannabis use.

Cannabis-alcohol co-use is common among young adults. Knowing that co-use amplifies intoxication and that the degree of amplification predicts future problematic use provides a basis for targeted harm reduction messaging.

Understanding that the timing between cannabis and alcohol use matters for intoxication levels provides practical harm reduction information. The link between co-use intoxication and future hazardous use suggests that co-use patterns could be an early warning sign.

Self-reported subjective effects via EMA. Relatively small sample. Cannot control for doses of each substance. Young adult sample may not generalize to older adults.