This study examined the prospective relations among family history density of
alcoholism (
FHD), adolescent family harmony, and young adults' alcohol and
drug dependence. Family harmony was rated by mothers and fathers in adolescence, and young adults'
substance dependence diagnoses were obtained through structured interviews. Higher
FHD predicted lower adolescent family harmony, which in turn increased young adults' odds of being diagnosed with
drug dependence (with and without
alcohol dependence) compared to no diagnoses or to
alcohol dependence only. Family harmony also interacted with
FHD such that the protective effect of family harmony on young adults'
drug dependence with or without
alcohol dependence decreased as
FHD rose, and was nonsignificant at high levels of
FHD. The findings suggest the importance of distinguishing among alcohol and
drug dependence disorders and examining their differential etiological pathways, and also suggest that the protective effects of harmonious family environments on
substance dependence may be limited at high levels of
FHD.