title: Understanding cannabis use in first-episode psychosis: an application of the Theory of Planned Behaviour.
abstract: OBJECTIVE
  The study aims to examine whether an extended Theory of Planned Behaviour (TPB) model predicts the frequency of past and intended cannabis use in young adults with psychosis.
  
  
  METHODS
  A cross-sectional correlational design was used with 32 participants (aged 18-36 years old) within 3 years (mean = 7 months) of their first psychotic episode. TPB variables and a measure of social influence (descriptive norms) were measured.
  
  
  RESULTS
  The TPB accounted for a large amount of the variance in both the frequency of past cannabis use (25%) and in the intended frequency of future cannabis use (36%). The addition of descriptive norms (beliefs about the frequency of others' cannabis use) accounted for a significant additional amount of the variance in past use (19%). Adding the 'friends' component of descriptive norms only led to a model that accounted for 52% of the variance in past cannabis use.
  
  
  CONCLUSIONS
  Descriptive social norms should be considered when trying to understand cannabis use in early psychosis. Interventions should take account of the individual's attitude towards cannabis, their perceived control over its use and its social context.
authors.affiliation: Royal Holloway, University of London, London, UK.
authors.forename: Anna
authors.initials: A
authors.lastname: Hames
authors.forename: Michael
authors.initials: M
authors.lastname: Evangeli
authors.forename: Chris
authors.initials: C
authors.lastname: Harrop
authors.forename: Marta
authors.initials: M
authors.lastname: di Forti
mesh_terms: D000293:Adolescent; D000328:Adult; D017831:Diagnosis, Dual (Psychiatry) / Q000523:psychology; D042241:Early Diagnosis; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000150:complications / Q000523:psychology*; D008960:Models, Psychological; D011582:Psychological Theory; D011618:Psychotic Disorders / Q000150:complications / Q000175:diagnosis / Q000523:psychology*; D012945:Social Values