title: Course of cannabis use and clinical outcome in patients with non-affective psychosis: a 3-year follow-up study.
abstract: BACKGROUND
  Prospective studies on the relationship between course of cannabis use and clinical outcome in patients with non-affective psychotic disorders are inconclusive. The current study examined whether (1) persistent, recently started, discontinued and non-cannabis-using patients with a psychotic disorder differed with regard to illness outcome at 3-year follow-up, and (2) whether timing of cannabis discontinuation was associated with course of clinical outcome.
  
  
  METHODS
  This 3-year follow-up study was part of a multi-center study in the Netherlands and Belgium (Genetic Risk and Outcome of Psychosis; GROUP). We used mixed-model analyses to investigate the association between pattern of cannabis use and symptoms, global functioning and psychotic relapse.
  
  
  RESULTS
  In our sample of 678 patients, we found persistent users to have more positive and general symptoms, worse global functioning and more psychotic relapses compared with non-users and discontinued users [Positive and Negative Syndrome Scale (PANSS) positive, p < 0.001; PANSS general, p < 0.001; Global Assessment of Functioning (GAF) symptoms, p = 0.017; GAF disability, p < 0.001; relapses, p = 0.038]. Patients who started using cannabis after study onset were characterized by worse functioning at baseline and showed an increase in general symptoms (including depression and anxiety) at the 3-year follow-up (p = 0.005). Timing of cannabis discontinuation was not associated with clinical outcome.
  
  
  CONCLUSIONS
  These findings suggest that cannabis use in patients with a psychotic disorder has a long-lasting negative effect on illness outcome, particularly when persistent. Treatment should focus on discouraging cannabis use.
authors: Department of Early Psychosis,Academic Medical Center,Amsterdam,The Netherlands.
authors: F J
authors: FJ
authors: van der Meer
authors: Department of Early Psychosis,Academic Medical Center,Amsterdam,The Netherlands.
authors: E
authors: E
authors: Velthorst
mesh_terms: D000328:Adult; D001007:Anxiety / Q000523:psychology; D001530:Belgium / Q000453:epidemiology; D016022:Case-Control Studies; D003863:Depression / Q000523:psychology; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D002189:Marijuana Abuse / Q000453:epidemiology / Q000523:psychology*; D008385:Marijuana Smoking / Q000453:epidemiology / Q000523:psychology*; D009426:Netherlands / Q000453:epidemiology; D011446:Prospective Studies; D011618:Psychotic Disorders / Q000453:epidemiology / Q000523:psychology*; D012189:Retrospective Studies; D055815:Young Adult
keywords: Cannabis; clinical outcome; psychosis; psychotic relapse; schizophrenia; symptoms