This research is not without limitations. The SIBS sample is predominantly in mid-adolescence, so all participants have not yet experienced the full risk period for substance misuse. Consequently, our analysis of substance use necessarily focused on ever using rather than patterns of regular use or abuse. Further, behavioral genetic research suggests that the impact of family environmental influences on substance use and mental health outcomes diminishes with age as genetic influences gain in importance40-42. It will be important to follow the SIBS sample through late adolescence and early adulthood as more of the participants initiate substance use and as others transition to regular or abusive use patterns to determine whether the effects we observe will endure.
