Working memory capacity predicts cannabis-induced effects on alcohol urge

Cannabis has shown mixed results in its association with alcohol urge, which may be explained by individual differences. One such factor, working memory capacity (WMC) is associated with drug-related cue reactivity and implicated in alcohol use and problems. In the current study, we examined whether WMC moderates the acute effect of cannabis on alcohol urge in a randomized placebo-controlled crossover trial.

Participants aged 21 to 44 (N = 125, 32 % female) reporting heavy alcohol use and cannabis use ≥ twice weekly completed a laboratory protocol across three days where they smoked a placebo, 3.1 % delta-9 tetrahydrocannabinol (THC), and 7.2 % THC cannabis cigarette. Participants were asked to rate their alcohol urge pre and post smoking. Prior to the experimental sessions, participants completed WMC measures including the n-back and the complex span tasks, operation span (OS) and symmetry span (SS).

Those with higher WMC, as assessed via the SS task, reported significantly lower alcohol urge after smoking the 7.2 %, but not the 3.1 %, THC dose, relative to placebo. Performance on the OS task was not associated with alcohol urge. Lower WMC as determined via n-back scores was associated with higher alcohol urge overall, but n-back scores did not moderate the impact of cannabis on alcohol urge.

Findings suggest individuals with higher but not lower working memory experience lower alcohol urge under acute effects of cannabis. Although cannabis is increasingly perceived as a substitute for alcohol, individuals with lower working memory may be less likely to experience such benefits when attempting to reduce their drinking.