Cannabis Use in Schizophrenia: More Positive Symptoms, Fewer Negative Symptoms in Large Meta-Analysis

Cannabis use was associated with higher positive symptom severity (aMD=0.38), lower negative symptom severity (aMD=-0.50), and higher excitement (aMD=0.16) using the 5-factor PANSS model. No significant associations were found with disorganization or depression dimensions. Effect sizes were small and confidence intervals wide.

Individual participant data meta-analysis (IPDMA) using raw datasets from 21 studies totaling 3,053 complete cases. PubMed, ScienceDirect, and PsycINFO searched through September 2022. Cannabis users required to have CUD diagnosis or use at least twice weekly. Outcomes assessed using both 3-factor and 5-factor PANSS structures with adjusted multivariate analysis.

This is the largest IPDMA on cannabis and schizophrenia symptoms to date. The finding that cannabis use is associated with lower negative symptoms (amotivation, flat affect) alongside higher positive symptoms (hallucinations, delusions) creates a complex picture with implications for treatment.

The lower negative symptoms associated with cannabis use could explain why some patients report subjective benefit from cannabis, as negative symptoms (social withdrawal, emotional flatness) are often the most distressing and treatment-resistant aspects of schizophrenia. However, the increased positive symptoms suggest this comes at a cost.

Cross-sectional associations cannot determine causation. Effect sizes are small with wide confidence intervals. Cannot rule out that people with fewer negative symptoms are simply more socially active and therefore more likely to access cannabis. Self-selection bias remains.