Risk factors for the onset of dependence and chronic psychosis due to cannabis use: Survey of patients with cannabis‐related psychiatric disorders

AIM: The objective of the current study was to identify risk factors that affect the onset of dependence and chronic psychosis due to cannabis use. METHODS: We examined clinical genetic factors, psychiatric disorders prior to cannabis use, starting age of cannabis use, duration and frequency of cannabis use, types of cannabis products used, combined use of other psychoactive substances, and the psychiatric diagnosis of 71 patients with cannabis‐related psychiatric disorders who underwent treatment at nine mental health hospitals in Japan. Information was collected from cross‐sectional interview surveys conducted by each patient's attending psychiatrist. RESULTS: For the diagnosis of dependence syndrome due to the use of cannabis, we found associations with the number of years of cannabis use and the use of cannabis products with a high Δ9‐tetrahydrocannabinol (THC) content. However, we found no association between diagnosis of residual and late‐onset psychotic disorders and clinical genetic factors, presence of preceding psychiatric disorders, duration and frequency of cannabis use, starting age of cannabis use, or combined use of other psychoactive substances; an association was found only for the absence of use of cannabis products other than dried cannabis. CONCLUSION: The onset of cannabis dependence was related to long‐term cannabis use and the use of cannabis products with a high THC content. However, chronic psychosis was not associated with total THC intake or psychiatric vulnerability. Thus, unknown factors appear to be involved in the onset of chronic psychosis.