Childhood adversity and cannabis use are both known risk factors for psychosis. This study examined whether cannabis use might explain the link between childhood adversity and psychotic disorders. Data from 881 first-episode psychosis patients and 1231 controls from the EU-GEI study showed that household discord was associated with psychosis partly through cannabis use. Lifetime cannabis use mediated 17% of the association, cannabis potency mediated 14%, and frequency of use mediated 29%. Similar results appeared for early exposure to household discord. The findings suggest that harmful cannabis use patterns partially explain how household discord leads to psychosis, and children exposed to challenging home environments could benefit from interventions to prevent cannabis misuse.
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.
Heavy use of high-potency cannabis that is high in THC and low in CBD increases the risk of psychotic disorders, with greater risk for early use and use of synthetic cannabinoids. Frequent cannabis use also raises the risk for mania and suicide, but the effect on depression is less clear and findings on anxiety are contradictory. Depression and anxiety may lead to greater cannabis consumption in some studies. THC interacts with genetic predisposition and other environmental factors, while CBD may reduce the psychotogenic effects of THC but is absent from many high-potency varieties. The evidence is strong enough to merit public health education about psychosis risk.