Young psychosis patients who use cannabis have worse cognitive function than non-using patients

Systematic search of 308 studies identified 14 comparing neurocognition between current cannabis users and non-users with psychotic disorders, with mean age between 15 and 45 years. Effect sizes were extracted from cognitive test performance and analyzed using random effects modeling with moderator analyses.

Understanding the cognitive effects of cannabis in psychosis is important for treatment planning and for understanding the biology of cannabis-associated psychosis. If cannabis-using patients have worse cognition, this challenges the idea that they represent a "healthier" subgroup and suggests cannabis may actively impair cognitive function on top of psychosis-related deficits.

This meta-analysis helps resolve a confusing finding in the literature. The earlier observation that cannabis-using psychosis patients had better cognition likely reflected a comparison of lifetime users (many of whom had stopped) rather than current users. When the analysis focuses on those actively using cannabis, the cognitive picture is worse, suggesting cannabis compounds psychosis-related cognitive impairment.

The studies used varied cognitive assessments, making direct comparison imperfect. The age range (15-45) is broad. Current cannabis use was defined differently across studies. The meta-analysis cannot determine whether cannabis caused the cognitive deficits or whether patients with worse cognition were more likely to continue using. Sample sizes within individual studies varied.