title: Cannabis-induced psychosis and subsequent schizophrenia-spectrum disorders: follow-up study of 535 incident cases.
abstract: BACKGROUND
  Few studies have examined samples of people with cannabis-induced psychotic symptoms.
  
  
  OBJECTIVE
  To establish whether cannabis-induced psychotic disorders are followed by development of persistent psychotic conditions, and the timing of their onset.
  
  
  METHODS
  Data on patients treated for cannabis-induced psychotic symptoms between 1994 and 1999 were extracted from the Danish Psychiatric Central Register. Those previously treated for any psychotic symptoms were excluded. The remaining 535 patients were followed for at least 3 years. In a separate analysis, the sample was compared with people referred for schizophrenia-spectrum disorders for the first time, but who had no history of cannabis-induced psychosis.
  
  
  RESULTS
  Schizophrenia-spectrum disorders were diagnosed in 44.5% of the sample. New psychotic episodes of any type were diagnosed in 77.2%. Male gender and young age were associated with increased risk. Development of schizophrenia-spectrum disorders was often delayed, and 47.1% of patients received a diagnosis more than a year after seeking treatment for a cannabis-induced psychosis. The patients developed schizophrenia at an earlier age than people in the comparison group (males, 24.6 v. 30.7 years, females, 28.9 v. 33.1 years).
  
  
  CONCLUSIONS
  Cannabis-induced psychotic disorders are of great clinical and prognostic importance.
authors.affiliation: Aarhus University Hospital, Skovagervej 2, DK-824 0 Risskov, Denmark. mca@psykiatri.aaa.dk
authors.forename: Mikkel
authors.initials: M
authors.lastname: Arendt
authors.forename: Raben
authors.initials: R
authors.lastname: Rosenberg
authors.forename: Leslie
authors.initials: L
authors.lastname: Foldager
authors.forename: Gurli
authors.initials: G
authors.lastname: Perto
authors.forename: Povl
authors.initials: P
authors.lastname: Munk-Jørgensen
mesh_terms: D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D002188:Cannabis / Q000009:adverse effects*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D002189:Marijuana Abuse / Q000150:complications* / Q000453:epidemiology; D011618:Psychotic Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology*; D012008:Recurrence; D012307:Risk Factors; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology*; D012737:Sex Factors