title: Cannabis users have higher premorbid IQ than other patients with first onset psychosis.
abstract: BACKGROUND
  A number of studies have reported that patients with psychosis who use cannabis have better cognitive performance than those who do not. This is surprising as cannabis can impair cognition in healthy subjects. An obvious question is whether the better current performance of psychotic patients who have used cannabis is a reflection of their having a higher premorbid IQ than those psychotic patients who haven't used cannabis.
  
  
  OBJECTIVE
  In a sample of patients at their first episode of psychosis, we tested the hypothesis that patients who smoked cannabis would have a higher premorbid IQ than patients who did not.
  
  
  METHODS
  279 participants (119 patients and 160 healthy controls) were assessed in order to obtain current and premorbid IQ measures and detailed information on cannabis use. We examined the association between cannabis use and both premorbid and current IQ in patients and controls.
  
  
  RESULTS
  Patients who had ever smoked cannabis had significantly higher current (p<.001) and premorbid IQ (p=.004) compared to patients who had never used cannabis. This difference was not found among controls.
  
  
  CONCLUSIONS
  These findings suggest that the better cognitive performance of patients with their first episode of psychosis who have used cannabis compared with those who haven't is due to the better premorbid IQ of the former.
authors: Institute of Psychiatry, Department of Psychosis Studies and Biomedical Research Centre, King's College, de Crespigny Park, Denmark Hill, London SE5 8AF, United Kingdom; Sezione di Psichiatria del Dipartimento di Biomedicina Sperimentale e Neuroscienze Cliniche (BioNeC), Università di Palermo, Via "Gaetano La Loggia" 1, 90100 Palermo, Italy. Electronic address: laura_ferraro@hotmail.it.
authors: Laura
authors: L
authors: Ferraro
authors: Manuela
authors: M
authors: Russo
authors: Jennifer
authors: J
authors: O'Connor
authors: Benjamin D R
authors: BD
authors: Wiffen
authors: Maria Aurora
authors: MA
authors: Falcone
authors: Lucia
authors: L
authors: Sideli
authors: Poonam
authors: P
authors: Gardner-Sood
authors: Simona
authors: S
authors: Stilo
authors: Antonella
authors: A
authors: Trotta
authors: Paola
authors: P
authors: Dazzan
authors: Valeria
authors: V
authors: Mondelli
authors: Heather
authors: H
authors: Taylor
authors: Bess
authors: B
authors: Friedman
authors: Hannah
authors: H
authors: Sallis
authors: Caterina
authors: C
authors: La Cascia
authors: Daniele
authors: D
authors: La Barbera
authors: Anthony S
authors: AS
authors: David
authors: Abraham
authors: A
authors: Reichenberg
authors: Robin M
authors: RM
authors: Murray
authors: Marta
authors: M
authors: Di Forti
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D003071:Cognition / Q000502:physiology*; D005260:Female; D006801:Humans; D007360:Intelligence / Q000502:physiology*; D007361:Intelligence Tests; D008297:Male; D002189:Marijuana Abuse / Q000523:psychology*; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D011618:Psychotic Disorders / Q000503:physiopathology* / Q000523:psychology*; D055815:Young Adult
keywords: Cannabis; Cognition; First Episode of Psychosis (FEP); IQ; Premorbid IQ; Risk of psychosis; Schizophrenia; Substance use