title: The impact of cannabis and stimulant disorders on diagnostic stability in psychosis.
abstract: BACKGROUND
  Substance abuse adds to diagnostic uncertainty in psychosis and may increase the risk of transition from brief and affective psychoses to schizophrenia. This study examined whether comorbid substance disorder was associated with diagnostic instability and progression from other psychosis diagnoses to schizophrenia and whether effects differed for cannabis and stimulant-related disorders.
  
  
  METHODS
  We identified 24,306 individuals admitted to hospital with an ICD-10 psychosis diagnosis between 2000 and 2011. We examined agreement between initial diagnosis and final diagnosis over 2-5 years and predictors of diagnostic change toward and away from a final diagnosis of schizophrenia.
  
  
  RESULTS
  Nearly half (46%) of participants with initial brief, atypical, or drug-induced psychoses were later diagnosed with schizophrenia. Persisting illicit drug disorders did not increase the likelihood of progression to schizophrenia (OR = 0.97; 95% CI, 0.89-1.04) but increased the likelihood of revision of index psychosis diagnosis away from schizophrenia (OR = 1.55; 95% CI, 1.40-1.71). Cannabis disorders predicted an increased likelihood of progression to schizophrenia (OR =1.12; 95% CI, 1.01-1.24), while stimulant disorders predicted a reduced likelihood (OR = 0.81; 95% CI, 0.67-0.97). Stimulant disorders were associated with greater overall diagnostic instability.
  
  
  CONCLUSIONS
  Many people with initial diagnoses of brief and affective psychoses are later diagnosed with schizophrenia. Cannabis disorders are associated with diagnostic instability and greater likelihood of progression to schizophrenia. By contrast, comorbid stimulant disorders may be associated with better prognosis in psychosis, and it may be important to avoid premature closure on a diagnosis of schizophrenia when stimulant disorders are present.
authors.affiliation: InforMH, Macquarie Hospital, PO Box 169, North Ryde NSW 1670 Australia (Grant.Sara@health.nsw.gov.au).
authors.forename: Grant E
authors.initials: GE
authors.lastname: Sara
authors.forename: Philip M
authors.initials: PM
authors.lastname: Burgess
authors.forename: Gin S
authors.initials: GS
authors.lastname: Malhi
authors.forename: Harvey A
authors.initials: HA
authors.lastname: Whiteford
authors.forename: Wayne C
authors.initials: WC
authors.lastname: Hall
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000150:complications* / Q000175:diagnosis / Q000523:psychology; D008875:Middle Aged; D011618:Psychotic Disorders / Q000150:complications / Q000175:diagnosis* / Q000523:psychology; D012189:Retrospective Studies; D012559:Schizophrenia / Q000150:complications / Q000175:diagnosis; D012565:Schizophrenic Psychology; D019966:Substance-Related Disorders / Q000150:complications / Q000175:diagnosis / Q000523:psychology; D055815:Young Adult