Ancestry-stratified analyses demonstrated consistent main and interaction effects in the European American subpopulation (N=1,130). In the interaction model set for European American individuals, peer drinking had a hazardous effect on first intoxication (HR=1.87, 95% 1.66–2.11) and first DSM-5 symptom (HR=2.23, 95% CI 1.89–2.63); rs1229984 had a protective effect on first intoxication (HR=0.60, 95% CI 0.44–0.82) and first DSM-5 symptom (HR=0.47, 95% CI 0.27–0.82); and interaction terms were significant (p<.02). The ADH1B GA/AA genotypes were protective among individuals reporting none/few best friends drinking, but not among those reporting most/all best friends drinking, corroborating our findings in the overall sample.
