title: Does giving up substance use work for patients with psychosis? A systematic meta-analysis.
abstract: OBJECTIVE
  To assess the extent to which ceasing the use of cannabis or other substances reduces the symptoms and social disability associated with psychotic illness.
  
  
  METHODS
  The electronic databases CINAHL, EMBASE, MEDLINE and PsycINFO were searched for peer-reviewed publications in English that report data about the characteristics of current and former substance-using patients diagnosed with psychotic illnesses. The searches yielded 328 articles, of which 23 studies met the inclusion criteria. Four key outcome variables; positive symptoms, negative symptoms, ratings of depression and global function, and five other measures of outcome that were reported in five or more studies were examined using meta-analysis.
  
  
  RESULTS
  Current substance-using patients were significantly younger than former substance-using patients (standardised mean difference (SMD) = -0.38), but did not differ in age at onset of psychosis, sex, level of education or marital status. Current substance users had higher scores on rating scales of positive symptoms (SMD = 0.29) and depression (SMD = 0.36), and lower scores on global function (SMD = -0.26) when compared with former substance users. There was a significant improvement in the ratings of positive symptoms, mood and global function among patients who stopped using substances during the first episode of psychosis, while improvements in the symptoms of patients with a more established psychotic illness did not reach statistical significance.
  
  
  CONCLUSIONS
  The results suggest that substance use contributes to both the symptoms and the burden of disability experienced by patients with psychosis. Patients in the early stages of psychotic illness should be informed about the benefits of giving up substances earlier, rather than later in the illness. Psychiatric services should regard the treatment of substance use as an integral part of the treatment of psychotic disorders.
authors.affiliation: The Prince of Wales Hospital, Barker Street, Randwick, Sydney, Australia.
authors.forename: Katherine
authors.initials: K
authors.lastname: Mullin
authors.forename: Pal
authors.initials: P
authors.lastname: Gupta
authors.forename: Michael T
authors.initials: MT
authors.lastname: Compton
authors.forename: Olav
authors.initials: O
authors.lastname: Nielssen
authors.forename: Anthony
authors.initials: A
authors.lastname: Harris
authors.forename: Matthew
authors.initials: M
authors.lastname: Large
mesh_terms: D006801:Humans; D011618:Psychotic Disorders / Q000150:complications / Q000523:psychology*; D012720:Severity of Illness Index; D019966:Substance-Related Disorders / Q000150:complications / Q000523:psychology*