Cannabis use is associated with an increased risk of developing psychotic disorders among people already at clinical high risk for psychosis. In a prospective study of this population, cannabis use was linked to a higher incidence of psychotic disorders and to more persistent psychotic symptoms, as well as poorer functional outcomes. The findings strengthen evidence that cannabis acts as a risk factor for psychosis, though the direction of causality remains debated.
Genetic risk for schizophrenia and cannabis use each contribute to specific symptom patterns across psychotic disorders, not just diagnostic categories. Among 617 first-episode psychosis patients, higher schizophrenia polygenic risk scores were linked to more severe negative and positive symptoms, regardless of diagnosis. In 979 controls, the same genetic risk was associated with all dimensions of psychotic experiences. Daily or current cannabis use was tied to more positive symptoms in both patients and controls, beyond the effect of genetic risk. The findings support a dimensional view of psychosis, where genetic liability relates to symptom severity and cannabis use specifically increases positive symptoms.