Although these findings highlight the relative differences in impact genetic, shared- and non-shared environmental factors have on the diversity of substances used between males and females and across ages, from these analyses we can not discern the identity of the environmental influences and genetic polymorphisms that account for these observed differences, nor how these genetic and environmental influences interact. Relationships between substance use and environmental factors such as deviant peers (e.g. 24–27), parental factors (e.g. 24–28), and socioregional location (e.g. 29, 30) have been documented and may moderate the longitudinal etiology of diversity of substances used.
