The federal government's plan to legalize marijuana contravenes Canada's pledge to adhere to existing drug-control conventions set forth by the UN, according to a commentary published Monday in the CMAJ medical journal.

Canada is legally obligated to follow three international treaties that control or prohibit the access to drugs like marijuana, says the commentary's authors — Steven Hoffman and Roojin Habibi of the Global Strategy Lab at the University of Ottawa's Centre for Health Law, Policy and Ethics.

Those treaties are the 1961 Single Convention on Narcotic Drugs, the 1971 Convention on Psychotropic Substances and the 1988 Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.

Countries that adopted the 1961 convention, including Canada, agreed to recognize "addiction to narcotic drugs constitutes a serious evil for the individual and is fraught with social and economic danger" and be "conscious of their duty to prevent and combat this evil."

Canada would join other jurisdictions that have...