Behavioral symptoms of child mental disorders and lifetime substance use in adolescence: A within-family comparison of US siblings.

BACKGROUND: Childhood attention deficit hyperactivity disorder (ADHD) is found to be a risk factor for substance use in adolescence, but literature has suggested that the observed influence of ADHD may be driven by the comorbid conduct disorder (CD) or oppositional defiance disorder (ODD). We examine whether childhood ADHD and CD influence lifetime use of substances, independent of other comorbid mental problems and familial risk factors.

METHODS: A total of 712 sibling pairs from a nationally representative US longitudinal survey were followed from 1997 to 2015. The Behavior Problems Index (BPI) was used to measure mental disorders in children. The hyperactive, antisocial, headstrong, anxious/depressed subscales of the BPI for ADHD, CD, ODD, anxiety/depression of children were assessed by their biological mothers who were the primary caregiver. Lifetime substance use by age 18 was measured by self-reports. A within-family design was used to minimize confounding.

RESULTS: After controlling for mother fixed effects and comorbid mental disorders, symptoms of ADHD were not associated with lifetime substance use in adolescence except for regular smoking, while those of CD were positively and significantly associated with heightened risk for lifetime use of cannabis, regular smoking, cocaine, barbiturates, tranquilizers, hallucinogens, and inhalants in adolescence.

CONCLUSIONS: The results suggest that the association observed between childhood ADHD and substance use in adolescence may be driven by comorbid CD whose influences are robust to other mental disorders or unobserved familial factors.