Does frequent cannabis use affect thinking skills in heavy-drinking young adults?

Daily cannabis users showed significantly poorer working memory, more impulsive delay discounting, and greater ADHD symptom endorsement compared to non-users. Occasional users (monthly or weekly) did not differ from non-users on any measure. Effect sizes were small. Earlier age of cannabis initiation was not independently or interactively associated with worse performance.

Cross-sectional study of 598 high-risk drinking emerging adults (ages 21-25) categorized as non-users (n=276), occasional users (n=201), or daily users (n=121). Assessed working memory, attention, behavioral inhibition, delay and probability discounting, verbal intelligence, and ADHD symptoms. Controlled for age, race, sex, income, education, tobacco, and alcohol use.

This study separates daily from occasional use, revealing that the cognitive concerns about cannabis may be specific to heavy use patterns. The lack of deficits in occasional users challenges blanket warnings about any cannabis use damaging cognition.

In a sample already using alcohol heavily, cannabis effects on cognition appear dose-dependent. The absence of age-of-initiation effects challenges the common assumption that earlier exposure is categorically more harmful. However, cross-sectional data cannot determine whether daily cannabis use caused these deficits or whether people with pre-existing cognitive differences gravitate toward daily use.

Cross-sectional design cannot determine causation. All participants were heavy drinkers, limiting generalizability. Self-reported cannabis use categories. Small effect sizes suggest modest practical significance.