Male Cannabis Users Developed Schizophrenia Nearly 7 Years Earlier Than Male Non-Users

Population-based, first-contact incidence study conducted in The Hague, Netherlands. One hundred thirty-three patients were interviewed using the Comprehensive Assessment of Symptoms and History. Key informants were interviewed with the Instrument for the Retrospective Assessment of the Onset of Schizophrenia. Multivariate analyses controlled for the independent effects of gender and cannabis use on three illness milestones.

The finding that cannabis use independently predicted earlier onset of psychosis, even after controlling for gender differences, adds to evidence of a specific relationship between cannabis and the timing of psychotic episodes. The 6.9-year difference is clinically substantial, as earlier onset is generally associated with worse long-term outcomes.

This study is part of a growing body of evidence suggesting cannabis use is associated with earlier onset of schizophrenia, particularly in males. The population-based design strengthens the finding compared to clinic-based samples. Whether this represents a causal effect of cannabis or reflects shared vulnerability factors continues to be debated.

The cross-sectional design cannot establish causation. Cannabis use was assessed retrospectively, which introduces recall bias. The study cannot determine whether cannabis use precipitated psychosis in individuals who would not have developed it otherwise or simply accelerated onset in those already predisposed.