et al., 2007) and differences in sequence of licit and illicit substance initiation (Guerra et al., 2000) in African-Americans compared with Caucasians hint at distinctions in pathways of risk that cannot easily be detected in studies where African-Americans comprise only a small proportion of participants. In this study, we use data from a young adult African-American female twin sample to estimate the relative contributions of genetic and environmental factors to the timing of first use for alcohol, cigarettes, and cannabis and to assess the degree to which these influences on initiation are shared across the three substances.
