Despite the higher prevalence of cannabis use and cannabis use disorders than other illicit drug disorders in the general population [137] and the consistent evidence from twin and family studies of a heritable component to cannabis use and abuse/dependence, there has been less genomic research on cannabis use disorders than on cocaine and heroin disorders. There are several challenges facing genetic research into the etiology and course of cannabis (and other drug) use disorders. These include issues relating to research design, such as sample ascertainment, phenotype definition and statistical power (particularly an issue in the context of GWAS) as well as more fundamental issues relating to our understanding of risk for and development of cannabis (and other substance) use disorders
