“Throughout rigorous analyses, and after accounting for more than 70 variables in this longitudinal sample of children with ADHD taking stimulants, we did not find an association with later substance use,” lead investigator Brooke Molina, PhD, director of the youth and family research program at the University of Pittsburgh, said in an interview.
The findings were published online in JAMA Psychiatry.
Owing to symptoms of impulsivity inherent to ADHD, the disorder itself carries a risk for elevated substance use, the investigators note.
They speculate that this may be why some previous research suggests prescription stimulants reduce the risk of subsequent substance use disorder. However, other studies have found no such protective link.
To shed more light on the issue, the investigators used data from the Multimodal Treatment Study of ADHD, a multicenter, 14-month randomized clinical trial of medication and behavioral therapy for children with ADHD. However, for the purposes of the present study, investigators focused only on stimulant use in children.
At the time of recruitment, the children were aged 7-9 and had been diagnosed with ADHD between 1994 and 1996.
Investigators assessed the participants prior to randomization, at months 3 and 9, and at the end of treatment. They were then followed for 16 years and were assessed at years 2, 3, 6, 8, 10, 12, 14, and 16 until a mean age of 25.
During 12-, 14-, and 16-year follow-up, participants completed a questionnaire on their use of alcohol, marijuana, cigarettes, and several illicit and prescription drugs.
Investigators collected information on participants’ stimulant treatment via the Services for Children and Adolescents Parent Interview until they reached age 18. After that, participants reported their own stimulant treatment.
A total of 579 participants were included in the analysis. Of these, 61% were White, 20% were Black, and 8% were Hispanic.
Decline in stimulant use over time
The analysis showed that stimulant use declined “precipitously” over time – from 60% at the 2- and 3-year assessments to an average of 7% during early adulthood.
The investigators also found that for some participants, substance use increased steadily through adolescence and remained stable through early adulthood. For instance, 36.5% of the adolescents in the total cohort reported smoking tobacco daily, and 29.6% reported using marijuana every week.
In addition, approximately 21% of the participants indulged in heavy drinking at least once a week, and 6% reported “other” substance use, which included sedative misuse, heroin, inhalants, hallucinogens, or other substances taken to “get high.”
After accounting for developmental trends in substance use in the sample through adolescence into early adulthood with several rigorous statistical models, the researchers found no association between current or prior stimulant treatment and cigarette, marijuana, alcohol, or other substance use, with one exception.
While cumulative stimulant treatment was associated with increased heavy drinking, the effect size of this association was small. Each additional year of cumulative stimulant use was estimated to increase participants’ likelihood of any binge drinking/drunkenness vs. none in the past year by 4% (95% confidence interval, 0.01-0.08; P =.03).
When the investigators used a causal analytic method to account for age and other time-varying characteristics, including household income, behavior problems, and parental support, there was no evidence that current (B range, –0.62-0.34) or prior stimulant treatment (B range, –0.06-0.70) or their interaction (B range, –0.49-0.86) was associated with substance use in adulthood.
Dr. Molina noted that although participants were recruited from multiple sites, the sample may not be generalizable because children and parents who present for an intensive treatment study such as this are not necessarily representative of the general ADHD population.