Although studies consistently document increasing genetic influence during adolescence on a variety of phenotypes, including substance-specific use such as drinking behavior, this pattern has yet to be documented in the context of diversity of substances used (16, 17). When estimating the relative impact of genetic and environmental influences on substance use behaviors, those few studies that do focus on adolescents either collapse across age ranges (e.g., 7, 8) or use narrow age bands (e.g. 13, 14). This results in a lack of information on how relative genetic and environmental influences may change during adolescence.
