No serious commentator doubts that cannabis is potentially damaging to the user. Like tobacco, it is typically smoked and thus shares the potential for lung disease. Like alcohol, it affects reaction times and may raise the risk of road accidents. Cannabis has also been associated with cognitive impairment, deterioration in education performance (van Ours and Williams 2008), and psychotic illness (Arsenault 2004). Moreover, cannabis is often – albeit contentiously – seen as a causal gateway to more serious drug use (Kandel 2002). The question is what to do about it?
Researchers, research funders and policymakers should give greater voice to the risks and harms associated with particular cannabis policies and to the evaluation of alternative regulatory frameworks. Given the decades of research and experience with cannabis prohibition, it seems reasonable to reorient the cannabis policy debate based on known policy-attributable harms rather than to continue to speculate on questions of causality between cannabis use and mental illnesses such as psychosis, depression, and related disorders, that will not be definitively answered any time soon