title: Cannabis use and transition to psychosis in people at ultra-high risk.
abstract: BACKGROUND
  Cannabis use is associated with an increased risk of developing a psychotic disorder but the temporal relationship between cannabis use and onset of illness is unclear. The objective of this study was to assess prospectively the influence of cannabis use on transition to psychosis in people at ultra-high risk (UHR) for the disorder.
  
  
  METHODS
  Lifetime and continued cannabis use was assessed in a consecutively ascertained sample of 182 people (104 male, 78 female) at UHR for psychosis. Individuals were then followed clinically for 2 years to determine their clinical outcomes.
  
  
  RESULTS
  Lifetime cannabis use was reported by 134 individuals (73.6%). However, most of these individuals had stopped using cannabis before clinical presentation (n=98, 73.1%), usually because of adverse effects. Among lifetime users, frequent use, early-onset use and continued use after presentation were all associated with an increase in transition to psychosis. Transition to psychosis was highest among those who started using cannabis before the age of 15 years and went on to use frequently (frequent early-onset use: 25%; infrequent or late-onset use: 5%; χ(2)1=10.971, p=0.001). However, within the whole sample, cannabis users were no more likely to develop psychosis than those who had never used cannabis (cannabis use: 12.7%; no use: 18.8%; χ(2)1=1.061, p=0.303).
  
  
  CONCLUSIONS
  In people at UHR for psychosis, lifetime cannabis use was common but not related to outcome. Among cannabis users, frequent use, early-onset use and continued use after clinical presentation were associated with transition to psychosis.
authors: Institute of Psychiatry, King's College London,London,UK.
authors: L R
authors: LR
authors: Valmaggia
authors: Institute of Psychiatry, King's College London,London,UK.
authors: F L
authors: FL
authors: Day
authors: Institute of Psychiatry, King's College London,London,UK.
authors: C
authors: C
authors: Jones
authors: Institute of Psychiatry, King's College London,London,UK.
authors: S
authors: S
authors: Bissoli
authors: Institute of Psychiatry, King's College London,London,UK.
authors: C
authors: C
authors: Pugh
authors: Institute of Psychiatry, King's College London,London,UK.
authors: D
authors: D
authors: Hall
authors: Institute of Psychiatry, King's College London,London,UK.
authors: S
authors: S
authors: Bhattacharyya
authors: Institute of Psychiatry, King's College London,London,UK.
authors: O
authors: O
authors: Howes
authors: Institute of Psychiatry, King's College London,London,UK.
authors: J
authors: J
authors: Stone
authors: Institute of Psychiatry, King's College London,London,UK.
authors: P
authors: P
authors: Fusar-Poli
authors: Institute of Psychiatry, King's College London,London,UK.
authors: M
authors: M
authors: Byrne
authors: Institute of Psychiatry, King's College London,London,UK.
authors: P K
authors: PK
authors: McGuire
mesh_terms: D000328:Adult; D002188:Cannabis / Q000009:adverse effects*; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D011605:Psychoses, Substance-Induced / Q000209:etiology; D011618:Psychotic Disorders / Q000209:etiology*; D012306:Risk; D055815:Young Adult