The Relationship between Alcohol-Cannabis Use and Stressful Events with the Development of Incident Clinical Psychosis in a Community-Based Prospective Cohort.

Objective: The aim of this study is to evaluate the associations between alcohol-cannabis use and forensic/stressful events with the risk of incident clinical psychosis during follow-up.

Method: A community-based sample (n: 2142) was screened for clinical psychosis (schizophrenia and other psychotic disorders, affective disorders with psychotic features) at baseline and follow-up. Thus, incident clinical psychosis cases to develop during follow-up (individuals with no clinical psychosis at the baseline assessment and with clinical psychosis at the follow-up assessment) were detected (n: 27). These cases and the controls who did not report any psychotic symptoms at the follow-up assessment (n: 1691) were compared for exposure to environmental risk factors during follow-up (total n: 1718).

Results: Individuals reporting heavy alcohol drinking or cannabis use during follow-up had significantly higher risk of incident clinical psychosis. The monthly frequency of drinking and cannabis use was also associated with the risk. Higher number of stressful life events exposed predicted higher risk of incident clinical psychosis. The risk of incident clinical psychosis was significantly higher in case of coexistence of two risk factors (heavy drinking, cannabis use, ≥3 stressful events), in comparison with the existence of a single risk factor (17.7 vs. 1.6%, p<0.001).

Conclusion: Heavy drinking, cannabis use, forensic events and stressful events were associated with the risk of incident clinical psychosis. The coexistence of multiple stressful events and disorders related to abuse of alcohol/cannabis should be considered as a warning for the development of clinical psychosis.