ADHD in childhood is prospectively linked to substance use, and depression in adolescence may be a risk factor that explains some of this risk. In this study, the mediating* effects of adolescent depressive symptoms on childhood ADHD and adulthood substance use were examined. Moderation† of ADHD-related risk for substance use in adolescence and adulthood based on elevated adolescent depressive symptoms was also studied.
This study was based on longitudinal data from the prospective 16-year follow-up of the Multimodal Treatment of ADHD (MTA) study‡ and included children with combined-type ADHD based on the Diagnostic and Statistical Manual of Mental Disorders – 4th Edition (DSM-IV; n = 547) and a local normative comparison group (LNCG; n = 258). The self-report Substance Use Questionnaire was adapted for the MTA study, and participants responded to questions about the frequency of use of alcohol, marijuana, cigarettes and a range of illicit prescription drugs. Adolescent depressive symptoms were assessed by the self-report 27-item Child Depression Inventory, which was rated when participants were aged <18 years. Symptoms of ADHD in adolescence were assessed using combined parent and teacher ratings from the Swanson, Nolan and Pelham Rating Scale. The Conners’ Adult ADHD Rating Scale was administered when participants were aged ≥18 years and assessed ADHD symptom persistence in young adults. The Diagnostic Interview Schedule for Children-Young Adult version was used to determine whether those with ADHD also had a diagnosis of depression, alcohol-use disorder, marijuana-use disorder, nicotine dependence or other substance-use disorder (SUD) in adulthood.
Mediating effects of adolescent depressive symptoms and risk of substance use in adulthood
- Depressive symptoms in adolescence did not mediate any associations between childhood ADHD (vs the LNCG) and substance-use outcomes in adulthood:
- Heavy drinking: regression coefficient estimate (Est) –0.25 (95% confidence interval [CI] –0.63 to 0.12)
- Marijuana use: Est 0.26 (95% CI –0.23 to 0.74)
- Daily smoking: Est 2.28 (95% CI 1.20 to 3.37; p < 0.006)
- Illicit drugs: Est –0.10 (95% CI –0.61 to 0.41).
- Adolescent depressive symptoms also did not mediate any associations between childhood ADHD with comorbid conduct disorder (CD)/oppositional defiant disorder (ODD) (vs ADHD only) and substance-use outcomes in adulthood:
- Heavy drinking: Est 0.09 (95% CI –0.33 to 0.52)
- Marijuana use: Est –0.09 (95% CI –0.65 to 0.47)
- Daily smoking: Est 0.52 (95% CI –0.70 to 1.74)
- Illicit drugs: Est 0.56 (95% CI –0.03 to 1.15).
- There was a predicted <4% increase in the odds of more frequent adult substance use due to elevated adolescent depressive symptoms attributed to childhood ADHD.
Moderating effects of adolescent depressive symptoms on ADHD–substance-use association
- For both the ADHD group and the LNCG, substance use was more frequent at specific times when adolescents experienced depressive symptoms that were more severe than usual, regardless of ADHD history.
- At the age of 17 years, use of the following substances was 14–65% more frequent when depressive symptoms were greater:
- Heavy drinking (Est 0.97; standard error [SE] 0.47; p < 0.05)
- Marijuana use (Est 0.96; SE 0.48; p < 0.05)
- Daily smoking (Est 1.30; SE 0.66; p < 0.05)
- Illicit drugs (Est 1.41; SE 0.60; p < 0.05).
- Adolescents with more severe depressive symptoms tended to use all substances evaluated (except alcohol) more frequently in adolescence for both the ADHD group and the LNCG.
- Predicted rates of substance use (except alcohol) in 17 year olds were 65–85% more frequent in those with higher average depressive symptoms in adolescence.
- Adolescent depressive symptoms moderated the effect of childhood ADHD on adulthood marijuana use only:
- Rates of weekly marijuana use were higher in the ADHD group and the LNCG at more severe depressive symptom levels.
- Participants with a history of childhood ADHD used more marijuana regardless of adolescent depressive symptoms. This was also true for young adults without childhood ADHD whose adolescent depressive symptoms were more severe.
- Young adults with no history of ADHD in childhood and few depressive symptoms in adolescence were less likely to use marijuana.
Major depression and SUDs in adulthood among those with ADHD
- There was no significant interaction between depression and ADHD persistence for any SUD.
- Depression was significantly associated with higher rates of nicotine dependence (odds ratio [OR] 3.02; 95% CI 1.22–7.51; p = 0.017), but not:
- Alcohol-use disorder (OR 1.67; 95% CI 0.78–3.56; p = 0.183)
- Marijuana-use disorder (OR 1.02; 95% CI 0.44–2.38; p = 0.964)
- Other SUD (OR 0.80; 95% CI 0.67–7.42; p = 0.19).
- Persistent ADHD symptoms were unrelated to nicotine dependence (OR 1.95; 95% CI 0.93–4.06; p = 0.075).
This study had several limitations. Although the analysis was adjusted for ADHD with and without comorbid CD or ODD, associations with other relevant diagnoses, such as anxiety, were not taken into account. Moreover, the difference in depressive symptom severity between the ADHD group and the LNCG was small, which suggests low power in detecting mediating and moderating effects. Similarly, the rates of major depressive disorder at mean age 25 years between the two groups were comparable, and few young adults had ADHD and depression. This suggests that there was also low power in testing the differences in rates of SUDs for those with and without depressive disorder.
The authors concluded that depression diagnoses in adulthood and ADHD persistence may operate as independent, additive correlates of risk of substance use. The authors suggested that these findings may indicate a limited role for depression and substance-use risk that adds to ADHD-related risk, but does not alter or explain it.
*A mediating role suggests that childhood ADHD predicts more severe depressive symptoms in adolescence and this leads to more frequent heavy drinking, marijuana use, other illicit drug use and daily smoking in adulthood
†A moderating role suggests that differences between adolescents with and without ADHD in adolescent and adult substance use depends upon the severity of depressive symptoms during adolescence, between- and within-persons
‡Included children aged 7–9.9 years with combined-type ADHD based on the DSM-IV at six sites in the US and Canada. Children were randomly assigned to one of four treatment groups: multicomponent behavioural treatment; systematic medication management; the combination of medication and behavioural treatment; or referral to usual community care. Children with ADHD were assessed at baseline prior to treatment randomisation, at 3 months, 9 months, the conclusion of the 14-month treatment phase, and 2, 3, 6, 8, 10, 12, 14 and 16 years after treatment randomisation. Children in the LNCG were recruited at the 2-year assessment and were age- and gender-matched to the children with ADHD
Howard AL, Kennedy TM, Macdonald EP, et al. Depression and ADHD-related risk for substance use in adolescence and early adulthood: concurrent and prospective associations in the MTA. J Abnorm Child Psychol 2019; Epub ahead of print.