title: The role of cannabis in cognitive functioning of patients with schizophrenia.
abstract: BACKGROUND
  Cognitive deficits are commonly found both in patients with schizophrenia (SCH) and in people with cannabis use disorders (CUD). Surprisingly, some small recent studies reported better cognitive performance in SCH patients with comorbid cannabis use disorders (SCH + CUD) compared to other SCH patients.
  
  
  OBJECTIVE
  The aim of the present study was to investigate the residual impact of CUD and specific patterns of consumption on cognition in a larger sample of SCH + CUD patients.
  
  
  METHODS
  We administered a cognitive test battery to 34 SCH and 35 currently abstinent SCH + CUD patients. We explored the association between patterns of cannabis consumption and cognitive performance. Potential confounds with influence on cognitive ability were assessed and controlled for.
  
  
  RESULTS
  SCH + CUD patients had poorer academic achievements and lower vocabulary scores, but they performed better in tests of verbal and working memory, visuomotor speed and executive function (p < .05). More frequent cannabis use was associated with better performance in attention and working memory tasks.
  
  
  CONCLUSIONS
  Although our findings might be interpreted as beneficial effect of cannabis use on cognition in patients with schizophrenia, we favorise an alternative interpretation: in our view, the better cognitive functioning of SCH + CUD patients may rather reflect a relatively lower vulnerability to psychosis compared to the SCH group. Lower vulnerability may correspond to a higher level of functioning such as cognitive ability. This conclusion is consistent with the view of cannabis playing a critical role in the manifestation of psychosis in at least some of the SCH + CUD patients.
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital of Cologne, Kerpener Str. 62, 50924, Cologne, Germany. thomas.schnell@uk-koeln.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Schnell
authors.forename: Dagmar
authors.initials: D
authors.lastname: Koethe
authors.forename: Jörg
authors.initials: J
authors.lastname: Daumann
authors.forename: Euphrosyne
authors.initials: E
authors.lastname: Gouzoulis-Mayfrank