Age of Onset of Cannabis Use Is Associated With Age of Onset of High-Risk Symptoms for Psychosis

Objective: Increasing interest in the prodromal stage of schizophrenia over the past decade led us to perform our study to monitor people at high risk for developing a psychosis. We hypothesized that cannabis use or a cannabis use disorder at a younger age relates to high-risk symptoms at a younger age. Method: People referred to the Academic Medical Centre in Amsterdam, the Netherlands, with an ultra-high risk (UHR) for psychosis were interviewed with the Composite International Diagnostic Interview to assess their cannabis consumption. The Interview for the Retrospective Assessment of the Onset of Schizophrenia was used to collect data about age of onset of high-risk or prodromal symptoms. Nine high-risk symptoms were selected and clustered because of their known relation with cannabis use. Results: Among the 68 included participants, 35 had used cannabis (51.5%), of whom 15 had used recently. Twenty-two participants had been cannabis abusers or cannabis-dependent (32.4%) in the past. Younger age at onset of cannabis use was related to younger age of onset of the cluster of symptoms (rho = 0.48, P = 0.003) and also to 6 symptoms individually (rho = 0.47 to 0.90, P < 0.001 to 0.04). Younger age at onset of a cannabis use disorder was related to younger age of onset of the cluster of symptoms (rho = 0.67, P = 0.001) and also to 6 symptoms individually (rho = 0.50 to 0.93, P = 0.007 to 0.03). Conclusion: Cannabis use or a cannabis use disorder at a younger age in a group with an UHR for transition to psychosis is related to onset of high-risk symptoms for psychosis at a younger age.