Smoking cannabis reduced alcohol consumption by up to 27% in a controlled trial of heavy drinkers

After overnight cannabis abstinence, smoking cannabis with 3.1% or 7.2% THC led to significantly less alcohol consumption compared to placebo, reducing intake by 19% and 27% respectively. High-dose THC also reduced alcohol urge immediately after smoking, though broader craving measures did not show significant effects.

Double-blind crossover RCT published in the American Journal of Psychiatry. 157 participants who reported heavy alcohol use and cannabis use at least twice weekly completed three experimental sessions with different THC doses (7.2%, 3.1%, 0.03% placebo). Each session included neutral and personalized alcohol cue exposure followed by an alcohol self-administration task. 138 completed two or more sessions.

This is the first controlled human study to establish a causal effect of cannabis on alcohol consumption. Published in the top psychiatry journal, it provides rigorous experimental evidence for a substitution effect that has previously only been observed in survey and epidemiological data.

Alcohol use disorder kills approximately 140,000 Americans annually. If cannabis can reliably reduce alcohol consumption, it could have significant harm-reduction potential, though the tradeoffs of substituting one substance for another remain debated.

Laboratory setting may not reflect real-world drinking. Participants were regular cannabis users, so results may not apply to cannabis-naive individuals. Short-term effects only; long-term substitution patterns not addressed. The study examined acute effects after overnight abstinence from cannabis.