Examination of cumulative effects of early adolescent depression on cannabis and alcohol use disorder in late adolescence in a community-based cohort.

BACKGROUND AND AIMS: Although they often co-occur, the longitudinal relationship between depression and substance use disorders during adolescence remains unclear. This study estimated the effects of cumulative depression during early adolescence (ages 13-15 years) on the likelihood of cannabis use disorder (CUD) and alcohol use disorder (AUD) at age 18.

DESIGN: Prospective cohort study of youth assessed at least annually between 6th and 9th grades (~ age 12-15) and again at age 18. Marginal structural models based on a counterfactual framework that accounted for both potential fixed and time-varying confounders were used to estimate cumulative effects of depressive symptoms over early adolescence.

SETTING: The sample originated from four public middle schools in Seattle, Washington, USA.

PARTICIPANTS: The sample consisted of 521 youth (48.4% female; 44.5% were non-Hispanic White).

MEASUREMENTS: Structured in-person interviews with youth and their parents were conducted to assess diagnostic symptom counts of depression during early adolescence; diagnoses of CUD and AUD at age 18 was based the Voice-Diagnostic Interview Schedule for Children. Cumulative depression was defined as the sum of depression symptom counts from grades 7-9.

FINDINGS: The past-year prevalence of cannabis and alcohol use disorder at the age 18 study wave was 20.9 and 19.8%, respectively. A 1 standard deviation increase in cumulative depression during early adolescence was associated with a 50% higher likelihood of CUD [prevalence ratio (PR) = 1.50; 95% confidence interval (CI) = 1.07, 2.10]. Although similar in direction, there was no statistically significant association between depression and AUD (PR = 1.41; 95% CI = 0.94, 2.11). Further, there were no differences in associations according to gender.

CONCLUSIONS: Youth with more chronic or severe forms of depression during early adolescence may be at elevated risk for developing cannabis use disorder compared with otherwise similar youth who experience fewer depressive symptoms during early adolescence.