The main effects on maximal alcohol consumption of all of the environmental risk factors increased substantially in strength from ages 12–14 to ages 15–17, as did the effects of both GR-AUD and GR-ExtD. The pattern of interactions remained relatively similar to that seen at ages 12–14 except that the weaker interactions between GR-AUD and low prosocial behavior, and between GR-Ext and low parental monitoring, disappeared. Our environmental measures were much more limited at ages 18–21 and 22–25 when most of the twins had moved out of the home. Despite strong main effects of alcohol availability and peer group deviance on alcohol consumption at these ages, no gene×environment interactions were observed.
