Aims: To explore the developmental relationships between early-onset depressive disorders and later use of addictive substances.Design, Setting, Participants: A sample of 1545 adolescent twins was drawn from a prospective, longitudinal study of Finnish adolescent twins with baseline assessments at age 14 and follow-up at age 17.5.
Measurements:At baseline, DSM-IV diagnoses were assessed with a professionally administered adolescent version of Semi-Structured Assessment for Genetics of Alcoholism (C-SSAGA-A). At follow-up, substance use outcomes were assessed via self-reported questionnaire.Findings: Early-onset depressive disorders predicted daily smoking (odds ratio 2.29, 95%CI 1.49-3.50, p<.001), smokeless tobacco use (OR = 2.00, 95%CI 1.32-3.04, p=.001), frequent illicit drug use (OR = 4.71, 95%CI 1.95-11.37, p=.001), frequent alcohol use (OR = 2.02, 95%CI 1.04-3.92, p=.037) and recurrent intoxication (OR = 1.83, 95%CI 1.18-2.85, p=.007) three years later. Odds ratios remained significant after adjustment for comorbidity and exclusion of baseline users. In within-family analysis of depression-discordant co-twins (analyses that control for shared genetic and familial background factors), early-onset depressive disorders at age 14 significantly predicted frequent use of smokeless tobacco and alcohol at age 17.5.
Conclusions:Our results suggest important predictive associations between early-onset depressive disorders and addictive substance use, and these associations appear to be independent of shared familial influences.