Momentary cannabis effects on alcohol use among adults trying to quit or cut back on drinking

Many individuals who couse alcohol and cannabis endorse using cannabis to drink less alcohol. However, cannabis use during or after alcohol treatment predicts worse alcohol outcomes. Examining whether cannabis use affects alcohol use, craving, and related cognitions within person will help clarify this discrepancy and inform treatment. We tested competing hypotheses in individuals' daily lives: cannabis as harm reduction (predicting decreased alcohol use/craving and increased alcohol-goal self-efficacy/motivation) versus cannabis as an obstacle to reducing alcohol consumption (predicting the opposite pattern).

We recruited N = 58 adults who used cannabis ≥3x/week and were in/seeking treatment or trying to quit or cut down on drinking (M_age = 27.3 years, 60% female, 72% non-Hispanic white). Participants completed ecological momentary assessment with 5+ daily reports for 21 days. Every momentary survey assessed self-reported cannabis use and quantity, alcohol use, alcohol craving, alcohol-goal self-efficacy, and alcohol-goal motivation.

Multilevel models demonstrated that momentary cannabis use predicted increased subsequent alcohol self-efficacy (b = 0.11, SE = 0.13, p < .001) and motivation (b = 0.06, SE = 0.03, p = .031) but increased odds of concurrent drinking (OR = 2.39, 95% CI = [1.58, 3.61], p < .001). In addition, more frequent cannabis use on a given day predicted lower same-day self-efficacy (b = -0.34, SE = 0.13, p = .008) and motivation (b = -0.28, SE = 0.12, p = .019).

Adults who are trying to quit or cut back on drinking might perceive that cannabis use supports alcohol reduction efforts. Instead, cannabis use appears to be an obstacle to reducing drinking. (PsycInfo Database Record (c) 2026 APA, all rights reserved).