The adverse health effects of cannabis use: What are they, and what are their implications for policy?

Background: The adverse health effects of cannabis are a source of contention in debates about policies towards the drug. Methods: This paper provides a review of epidemiological evidence on the major adverse health effects of cannabis use and considers its implications for policy. Results: The evidence strongly suggests that cannabis can adversely affect some users, especially adolescents who initiate use early and young adults who become regular users. These adverse effects probably include increased risks of: motor vehicle crashes, the development of cannabis dependence, impaired respiratory function, cardiovascular disease, psychotic symptoms, and adverse outcomes of adolescent development, namely, poorer educational outcomes and an increased likelihood of using other illicit drugs. Conclusions: Politically, evidence of adverse health effects favours the status quo in developed countries like Australia where cannabis policy has been framed by the media as a choice between two views: (1) either cannabis use is largely harmless to most users and so we should legalize, or at the very least decriminalize its use; or (2) it harms some of its users so we should continue to prohibit its use.