title: What has research over the past two decades revealed about the adverse health effects of recreational cannabis use?
abstract: OBJECTIVE
  To examine changes in the evidence on the adverse health effects of cannabis since 1993.
  
  
  METHODS
  A comparison of the evidence in 1993 with the evidence and interpretation of the same health outcomes in 2013.
  
  
  RESULTS
  Research in the past 20 years has shown that driving while cannabis-impaired approximately doubles car crash risk and that around one in 10 regular cannabis users develop dependence. Regular cannabis use in adolescence approximately doubles the risks of early school-leaving and of cognitive impairment and psychoses in adulthood. Regular cannabis use in adolescence is also associated strongly with the use of other illicit drugs. These associations persist after controlling for plausible confounding variables in longitudinal studies. This suggests that cannabis use is a contributory cause of these outcomes but some researchers still argue that these relationships are explained by shared causes or risk factors. Cannabis smoking probably increases cardiovascular disease risk in middle-aged adults but its effects on respiratory function and respiratory cancer remain unclear, because most cannabis smokers have smoked or still smoke tobacco.
  
  
  CONCLUSIONS
  The epidemiological literature in the past 20 years shows that cannabis use increases the risk of accidents and can produce dependence, and that there are consistent associations between regular cannabis use and poor psychosocial outcomes and mental health in adulthood.
authors.affiliation: The University of Queensland Centre for Youth Substance Abuse Research and The UQ Centre for Clinical Research, Herston, Australia; The National Addiction Centre, Kings College London, London, UK; National Drug and Alcohol Research Centre, University of New South Wales, New South Wales, Australia.
authors.forename: Wayne
authors.initials: W
authors.lastname: Hall
mesh_terms: D000014:Abnormalities, Drug-Induced / Q000453:epidemiology / Q000209:etiology; D000063:Accidents, Traffic / Q000706:statistics & numerical data; D001334:Automobile Driving / Q000706:statistics & numerical data; D001927:Brain Diseases / Q000139:chemically induced / Q000453:epidemiology; D002318:Cardiovascular Diseases / Q000139:chemically induced / Q000453:epidemiology; D003072:Cognition Disorders / Q000139:chemically induced / Q000453:epidemiology; D004522:Educational Status; D005260:Female; D047109:Fetal Development / Q000187:drug effects; D006801:Humans; D013287:Illicit Drugs / Q000009:adverse effects*; D002189:Marijuana Abuse / Q000453:epidemiology / Q000209:etiology; D008385:Marijuana Smoking / Q000009:adverse effects*; D009369:Neoplasms / Q000139:chemically induced / Q000453:epidemiology; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000453:epidemiology / Q000209:etiology; D011605:Psychoses, Substance-Induced / Q000453:epidemiology / Q000209:etiology; D011618:Psychotic Disorders / Q000453:epidemiology / Q000209:etiology; D012140:Respiratory Tract Diseases / Q000139:chemically induced / Q000453:epidemiology; D012307:Risk Factors; D012559:Schizophrenia / Q000139:chemically induced / Q000453:epidemiology
chemical_list: D013287:Illicit Drugs
keywords: Cannabis; dependence; drug-related harms; epidemiology; health risks; mental health