Whereas the social and legal status of a drug is an environmental factor, it profoundly influences causes of individual behavioral variation pertaining to its use, including genetic sources of this variation. It is the legal definition of substances as licit/illicit, reflecting social conventions and significance of related behaviors rather than drug properties or organismic reactions to drugs, that results in a corresponding pattern of genetic clustering of liabilities to the respective disorders, forming two genetically distinct albeit correlated groupings of dependence symptoms respectively for licit and illicit drugs (Kendler et al., 2007). It is thus likely that a change in a drug's legal status (such as those, e.g., that happened with alcohol related to Prohibition) would result in the respective addiction's migration to the genetically and etiologically different group.
