title: Cannabis use and cognitive function: 8-year trajectory in a young adult cohort.
abstract: OBJECTIVE
  To evaluate the relationship between change in cannabis use and changed cognitive performance over 8 years.
  
  
  METHODS
  We used survey methodology with a cohort design.
  
  
  METHODS
  An Australian community sample aged 20-24 years at baseline.
  
  
  METHODS
  We assessed cognitive performance with the California Verbal Learning Test (CVLT) (immediate and delayed), Spot-the-Word test (STW), Symbol Digit Modality test (SDMT) and Digit Backwards (DB). Groups of cannabis users were defined from self-reports across three waves as: 'never' (n= 420) 'remain light' (n= 71), 'former light' (n= 231), 'remain heavy' (n= 60), 'former heavy' (n= 60) and 'always former' (since start of study) (n= 657). Planned contrasts within mixed model repeated-measures analysis of variance was used for longitudinal analysis with an adjusted alpha of 0.01.
  
  
  RESULTS
  Data were obtained from 2404 participants with 1978 (82.3%) completing wave 3. At baseline there were significant differences between cannabis groups on CVLT (immediate and delayed) and SDMT. However, after controlling for education, gender, gender × group and gender × wave, there were no significant between-group differences and only CVLT immediate recall reached adjusted statistically significant longitudinal change associated with changed cannabis use (group × wave P= 0.007). Specifically, former heavy users improved their performance relative to remaining heavy users (estimated marginal means: former heavy 6.1-7.5: remain heavy 6.4-6.6).
  
  
  CONCLUSIONS
  Cessation of cannabis use appears to be associated with an improvement in capacity for recall of information that has just been learned. No other measures of cognitive performance were related to cannabis after controlling for confounds.
authors.affiliation: Centre for Mental Health Research, Australian National University, Eggleston Road, Canberra, ACT, Australia. robert.tait@anu.edu.au
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Tait
authors.forename: Andrew
authors.initials: A
authors.lastname: Mackinnon
authors.forename: Helen
authors.initials: H
authors.lastname: Christensen
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001315:Australia / Q000453:epidemiology; D002188:Cannabis / Q000009:adverse effects*; D002648:Child; D003071:Cognition / Q000187:drug effects*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D059012:Lost to Follow-Up; D008297:Male; D002189:Marijuana Abuse / Q000453:epidemiology / Q000503:physiopathology* / Q000523:psychology; D008570:Memory, Short-Term / Q000187:drug effects; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data*; D013997:Time Factors; D014706:Verbal Learning / Q000187:drug effects; D055815:Young Adult