The Effects of Cannabis Use on Neurocognitive Functioning in Individuals with Schizophrenia

Cannabis use is highly prevalent among individuals with schizophrenia spectrum disorders (SSD), yet its impact on neurocognitive functioning remains unclear due to inconsistent findings in the literature. This systematic review and meta-analysis examined whether cannabis use is associated with differences in cognitive performance among individuals with SSD by comparing cannabis-using (SSD+CUD) and non-using (SSD-only) groups across seven core cognitive domains: total cognition, attention/vigilance, working memory, speed of processing, verbal learning and memory, visuospatial memory, and reasoning/problem-solving. Twenty-three studies were included in the analysis, and standardized effect sizes were calculated using a random-effects model. The findings revealed no significant differences between groups in six of the seven domains. However, a small but statistically significant advantage in attention and vigilance was observed in the cannabis-using group (Hedges’ g = 0.17, p = 0.01), which may reflect cannabinoid- related effects, compensatory mechanisms, or premorbid differences. Substantial heterogeneity across studies suggests that factors such as sample characteristics, cannabis composition, and assessment methods influence outcomes. Overall, the results indicate that cannabis does not uniformly impair cognition in SSD. Instead, its effects appear to vary based on individual and contextual factors. Future studies should employ longitudinal and stratified designs that account for variables such as age of onset, clinical profile, and cannabinoid content to better understand the nuanced relationship between cannabis use and cognitive functioning in this population. Keywords: cannabis use, schizophrenia, cognition, meta-analysis