In 75 years of cannabis prohibition in Canada, the latter third have been marked by considerable debate as to the propriety of invoking a criminal response to behaviour that is so prevalent and widely tolerated. The movement for reform of the laws prohibiting simple possession and use of the drug has intensified in recent years. Pragmatic adaptations on the part of Canadian legal institutions, aimed at mitigating the social and personal consequences of enforcing these sanctions, are applied routinely though selectively today. Nonetheless, actual policy reform seems far from inevitable, despite the increasing endorsement of factual evidence and widespread support for decriminalization. Given the legal-political impasse characterizing the cannabis controversy today, this paper examines the grounds on which prohibition may be viably opposed on the basis of respect for human rights. These moral grounds and remaining obstacles to legal reform are developed in view of the key contested arguments in R. v. Clay (1997), a landmark constitutional challenge as to the designation of cannabis as a prohibited substance in Canada.