Furthermore, the limited research in this area has not addressed the similarities (and distinctions) in the underlying variance structures of use and dependence for cannabis – and only rarely for alcohol (Grant et al., in press; Whitfield et al., 2004). Such a pursuit is highly relevant to gene association studies, as a large degree of genetic overlap between heaviness of use and dependence symptoms suggests that gene-finding studies for one phenotype can be directed by results from investigations of the other, perhaps even allowing for the integration of findings from studies of heavy use with those focused on dependence. The significant implications for etiological models of alcohol and cannabis dependence and the utility of global vs. substance-specific intervention strategies further highlight the importance of investigating commonality in sources of influence on alcohol and cannabis use and related symptomatology.
