title: The influence of early and frequent use of marijuana on the risk of desistance and of progression to marijuana-related harm.
abstract: BACKGROUND
  A significant minority of lifetime marijuana users will eventually receive a diagnosis of abuse or dependence. Yet little is known regarding the effect of age at onset and frequency of lifetime marijuana use on desistance from use and on progression to marijuana disorders.
  
  
  METHODS
  To address this issue, data were obtained from a community sample of 2,729 lifetime marijuana users participating in the Ontario Mental Health Supplement.
  
  
  RESULTS
  Early and frequent lifetime marijuana use was associated with highly persistent use and rapid progression to marijuana-related harm. Multivariate analyses revealed a monotonic increase in the risk of desistance with less frequent categories of use and later ages of onset. Results also indicated a threshold of use (100-199 times) associated with an elevated risk of developing marijuana disorders. A lower threshold of risk for marijuana problems was observed for females (50-99 times).
  
  
  CONCLUSIONS
  Early and frequent marijuana use are potent risk factors for prolonging desistance and hastening marijuana-related harm. Required are prevention programs aimed at delaying the onset of first use as well as harm reduction strategies that encourage cessation or reduced levels of consumption among those already using.
authors.affiliation: Social, Prevention and Health Policy Research Department, Centre for Addiction and Mental Health, London, Ontario, N6G 4X8. ddewit@julian.uwo.ca
authors.forename: D J
authors.initials: DJ
authors.lastname: DeWit
authors.forename: J
authors.initials: J
authors.lastname: Hance
authors.forename: D R
authors.initials: DR
authors.lastname: Offord
authors.forename: A
authors.initials: A
authors.lastname: Ogborne
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D003625:Data Collection; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000150:complications* / Q000175:diagnosis; D008875:Middle Aged; D015999:Multivariate Analysis; D009864:Ontario; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors