In the United States, the legal standing of cannabis is at a watershed with two states passing legislation permitting large scale commercialization (108) while in many other countries there is ongoing controversy surrounding the appropriate legal approach to recreational cannabis use (109). That cannabis use can be implicated in the (co)-occurrence of major psychiatric disorders (e.g. depression, psychosis), reduced life opportunities (e.g. low academic achievement) and death (e.g. suicide) are often cited as barriers to its legalization. A review of the literature quickly notes that while the evidence for a straightforward causal link between cannabis and these outcomes is tenuous at best (34), any rational public health policy regarding the regulation of cannabis cannot ignore these potential harms (110–112). What genetic studies do is shed light on these mechanisms. There is overwhelming support for a cluster of risk and protective influences, including familial, genetic and environmental factors that contribute to their co-occurrence. Thus, while genetic research may never put to bed the controversy surrounding the legality of cannabis use, nor should it, we believe that such studies have made and continue to substantially impact our understanding of the manner in which cannabis use and misuse produces societal and personal harm.
