Abstract
Aims: To examine whether major depressive disorder (MDD) and substance use disorders (SUDs: specifically, nicotine dependence (ND), alcohol use disorders (AUDs), and cannabis use disorders (CUDs)) in parents predicted increased risk for these disorders in late adolescent–emerging adult offspring and, specifically, the extent to which the pattern of risk differed for adopted and non-adopted youth. Participants: Late adolescent and emerging adult participants from the Sibling Interaction and Behavior Study (mean age=18.8), a community-based investigation of adopted and non-adopted adolescents, and their parents (adoptive parents of adopted youth, biological parents of non-adopted adolescents) were included. Measurements: Structured interviews were used to assess these disorders. Findings: (1) when the same disorder in parents and adolescents was examined, parental MDD was associated with increased risk for MDD among both adopted (p<.001) and non-adopted (p<.01) adolescents; in contrast, SUDs were associated with increased risk for the same SUD in non-adopted offspring (all p<.01). (2) When cross-SUD effects were examined, for the most part, each SUD was associated with increased risk for other SUDs among non-adopted but not adopted offspring (most p<.05). (3) When MDD-SUD associations were examined, parental ND and CUDs predicted increased risk for MDD in non-adopted (p<.001), but not adopted, adolescents. These effects tended to remain significant when adjusting for within-person comorbidity (p<.05). Conclusions: Major depressive disorder in parents appears to be a risk factor for late adolescent-emerging adult major depressive disorder but not substance use disorder in offspring, with this risk being environmentally mediated. Substance use disorder in parents appears, via genetic mediation, to increase risk of substance use disorder in adolescent offspring, and cannabis and nicotine use disorders in parents similarly contribute to major depressive disorder in those offspring.