title: Age at onset of non-affective psychosis in relation to cannabis use, other drug use and gender.
abstract: BACKGROUND
  Cannabis use is associated with an earlier age at onset of psychotic illness. The aim of the present study was to examine whether this association is confounded by gender or other substance use in a large cohort of patients with a non-affective psychotic disorder.
  
  
  METHODS
  In 785 patients with a non-affective psychotic disorder, regression analysis was used to investigate the independent effects of gender, cannabis use and other drug use on age at onset of first psychosis.
  
  
  RESULTS
  Age at onset was 1.8 years earlier in cannabis users compared to non-users, controlling for gender and other possible confounders. Use of other drugs did not have an additional effect on age at onset when cannabis use was taken into account. In 63.5% of cannabis-using patients, age at most intense cannabis use preceded the age at onset of first psychosis. In males, the mean age at onset was 1.3 years lower than in females, controlling for cannabis use and other confounders.
  
  
  CONCLUSIONS
  Cannabis use and gender are independently associated with an earlier onset of psychotic illness. Our findings also suggest that cannabis use may precipitate psychosis. More research is needed to clarify the neurobiological factors that make people vulnerable to this precipitating effect of cannabis.
authors.affiliation: Department of Psychiatry, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: N
authors.initials: N
authors.lastname: Dekker
authors.forename: J
authors.initials: J
authors.lastname: Meijer
authors.forename: M
authors.initials: M
authors.lastname: Koeter
authors.forename: W
authors.initials: W
authors.lastname: van den Brink
authors.forename: N
authors.initials: N
authors.lastname: van Beveren
authors.forename: R S
authors.initials: RS
authors.lastname: Kahn
authors.forename: D H
authors.initials: DH
authors.lastname: Linszen
authors.forename: J
authors.initials: J
authors.lastname: van Os
authors.forename: D
authors.initials: D
authors.lastname: Wiersma
authors.forename: R
authors.initials: R
authors.lastname: Bruggeman
authors.forename: W
authors.initials: W
authors.lastname: Cahn
authors.forename: L
authors.initials: L
authors.lastname: de Haan
authors.forename: L
authors.initials: L
authors.lastname: Krabbendam
authors.forename: I
authors.initials: I
authors.lastname: Myin-Germeys
mesh_terms: D000328:Adult; D017668:Age of Onset; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology*; D015985:Precipitating Factors; D011618:Psychotic Disorders / Q000453:epidemiology*; D012044:Regression Analysis; D012559:Schizophrenia / Q000453:epidemiology*; D012737:Sex Factors; D019966:Substance-Related Disorders / Q000453:epidemiology*