Temporal relationship of first-episode non-affective psychosis with cannabis use: A clinical verification of an epidemiological hypothesis

BackgroundWe analyzed the association of age at onset of psychosis treatment (AOPT) with having a history of cannabis use in patients with a first episode of non-affective psychosis. We also investigated the impact on the AOPT of exposure to cannabis in adolescence, compared with young adulthood, and of the additional exposure to cocaine.MethodWe recruited 112 consecutive patients (66 men and 46 women; age range, 18–57 years) with a first psychotic episode. The composite international diagnostic interview (CIDI) was used to assess drug use and to define the age at onset of heaviest use (AOHU) of a drug, defined as the age when drug was used the most for each patient. The effect of cannabis and cocaine AOHU on AOPT was explored through Kruskal–Wallis and Mann–Whitney tests, and logistic regression. Sex-adjusted cumulative hazard curves and Cox regression models were used to compare the AOPT of patients with and without a history of cannabis use, or associated cocaine use.ResultsWe found that the AOPT was significantly associated with the use of cannabis, independently of sex, use of cocaine, tobacco smoking or excessive alcohol consumption. There was a dose–response relationship between cannabis AOHU and AOPT: the earlier the AOHU the earlier the AOPT. Hazard curves showed that patients with a history of cannabis use had a higher hazard of having a first-episode psychosis than the rest of the patients (sex-adjusted log-rank χ2 = 23.43, df = 1, p < 0.001). Their respective median AOPT (25th, 75th percentiles) were 23.5 (21, 28) and 33.5 years (27, 45) (for log-transformed AOPT, t = 5.6, df = 110, p < 0.001). The sex-adjusted hazard ratio of psychosis onset comparing both groups was 2.66 (95% CI, 1.74–4.05).ConclusionsOur results are in favor of a catalytic role for cannabis use in the onset of psychosis.