title: [Residual neuropsychological, structural and functional brain abnormalities after long-term cannabis use].
abstract: BACKGROUND
  An important question that arises in policy discussions concerning the use of cannabis is whether the possible harmful effects of cannabis are reversible.
  
  
  OBJECTIVE
  To review studies on residual neuropsychological, structural and functional brain abnormalities that may have resulted from the long-term use of cannabis.
  
  
  METHODS
  When we searched Medline (January 1966 - December 2003) and EMBASE (January 1988 - December 2003) using the key words 'cannabis', 'marijuana', 'neuropsychological test', 'cognition', 'CT-scan', 'MRI', 'PET', 'SPECT' and 'brain', we found 29 studies in our area of interest. We selected only those neuropsychological and functional brain imaging studies in which the patients had a controlled abstinence period longer than 98 hours.
  
  
  RESULTS
  On the basis of six studies we concluded that there was insufficient evidence to prove conclusively that long-term cannabis use causes or does not cause residual abnormalities. The results of our review were also inconclusive whether cannabis use during adolescence may have a lasting effect on cognitive functioning and brain structure. However, we could not rule out the possibility that (1) certain cognitive and cerebral abnormalities existed in patients before cannabis use began and (2) that patients were suffering from subacute effects of cannabis.
  
  
  CONCLUSIONS
  So far, research into the residual effects of cannabis use has been inadequate. Future studies should concentrate on the effect of cannabis use during early adolescence. More insight should come from longitudinal studies involving neuropsychological measurements and brain imaging before cannabis use begins. The abstinence period should be at least seven weeks.
authors.affiliation: VU Medisch Centrum Amsterdam. marjanw@ggzba.nl
authors.forename: M R
authors.initials: MR
authors.lastname: Weeda
authors.forename: B D
authors.initials: BD
authors.lastname: Peters
authors.forename: L
authors.initials: L
authors.lastname: De Haan
authors.forename: D H
authors.initials: DH
authors.lastname: Linszen
mesh_terms: D000293:Adolescent; D001921:Brain / Q000254:growth & development / Q000503:physiopathology; D001923:Brain Chemistry / Q000187:drug effects; D003072:Cognition Disorders / Q000139:chemically induced / Q000175:diagnosis; D006801:Humans; D002189:Marijuana Abuse / Q000150:complications*; D001523:Mental Disorders / Q000139:chemically induced* / Q000175:diagnosis; D013997:Time Factors