Thus, reassessing the nature of the lifetime comorbidity in this sample after the respondents have had the time to encounter different substances has increased our ability to detect the latent dimension of risk. The common genetic and environmental influence on dependence vulnerability may be due genetic differences in the neural pathways, such as the mesolimbic dopaminergic system, that are influenced by most drugs of abuse (Chen et al., 2009). Likewise, non-shared or unique environmental contributions to SDV may be partially attributed to environmental circumstances, such as experiencing parental divorce (Thomson et al., 2008)) or childhood trauma (Khoury et al., 2010) that increase the likelihood of drug involvement. Simultaneously, the degree of substance-specific preference and substance-specific liability is also the consequence of one’s experiences and biology. Substance-specific genetic mechanisms most likely reflect differences in biological mechanisms that relay information specific to the presence or absence of a drug, as well as processes related to the metabolism of specific drugs, to name a few. Similarly, unique environmental influences on each drug may be capturing different environmental situations in which the use of these substances occurs.
