AGE OF ONSET OF PSYCHOSIS AND HISTORY OF CANNABIS USE IN A SAMPLE OF FIRST EPISODE PATIENTS IN BARCELONA

Abstract

Introduction: A number of observational studies have revealed an earlier onset of psychosis in schizophrenic patients with history of cannabis use. We evaluated whether use of cannabis determines an earlier onset of schizophrenia in a sample of first episode patients in an area with one of Europe’s highest rates of cannabis use. Methods: All first psychotic episode patients admitted in the case register of the Schizophrenia-Clinic Programme between 2002-2007 were assessed. Only those with confirmed diagnosis of schizophrenia (DSM-IV) were included in the analysis. Age at first antipsychotic treatment was used as proxy for age of psychosis onset, acting as dependent variable for the statistical analysis. Cannabis use was evaluated retrospectively considering period of greatest consumption: 46 (39.7%) had never used cannabis, 23 (19.9%) sporadically and 47 (40.5%) daily. Analysis of variance, polinomic lineal tendency analysis and individual post-hoc contrasts were performed. Results: The final sample included 116 subjects. Age of first antipsychotic treatment differed between groups (mean and [SD]: 27.0 [4.94]; 25.7 [4.44] and 24.5 [4.36]; p=0.033) and diminished as cannabis use increased (linear tendency; p=0.009). Post-hoc contrasts revealed that patients who had used cannabis (irrespective of frequency) had significantly lower ages of onset (p=0.033), ranging between 0.17 and 3.70 years (CI 95%). Conclusions: In our sample, cannabis use significantly decreased age of psychosis onset in schizophrenia. Prospective studies with larger samples are necessary to further study this association.