Emerging evidence shows that the 5-HTTLPR genotype interacts with social environments and influences drinking behaviors. However, few studies have examined interaction effects between the 5-HTTLPR genotype and specific aspects of family environments on adolescent drinking. The present study investigated whether the effects of family conflict or parental monitoring on adolescent drinking differed as a function of the 5-HTTLPR genotype cross-sectionally and longitudinally. It was replicated in two independent samples consisting of 175 adolescents in the U.S. and 4,916 adolescents in the U.K. The results of path analyses and multi-group analyses showed that, in the two samples, the 5-HTTLPR low-activity allele carriers exposed to high levels of family conflict were more likely to engage in concurrent alcohol misuse at Time 1 than non-carriers. The results of analyses testing the interaction between the 5-HTTLPR genotype and parental monitoring were inconsistent in the two samples. Overall, our results suggest that the 5-HTTLPR low activity allele carriers are more susceptible to the effect of family conflict on concurrent alcohol misuse. This finding highlights the importance of identifying and reducing family conflict in alcohol prevention and intervention programs in adolescents with the 5-HTTLPR low-activity allele
