The Effects of Stimulant Medications for ADHD

In recent years, mental disabilities have overtaken physical disabilities as the leading cause of activity limitations for children. One of the most prevalent mental conditions affecting children is Attention Deficit Hyperactivity Disorder (ADHD). As the number of children diagnosed with the condition has increased, so too has the use of stimulant medications such as Ritalin to treat the condition. In 2011, eleven percent of U.S. children ages 4 to 17 had ever been diagnosed with ADHD and more than half were taking stimulant medication.

Although stimulant medication is recommended as a treatment for ADHD by the National Institute of Mental Health, its use remains controversial. One concern is short- and long-term side effects, which may include physical effects such as decreased appetite, insomnia, and growth deficits as well as mood changes such as anxiety and depression. Adding to the unease is the relative lack of evidence on the educational benefits of medication use. Solid evidence can be difficult to come by because few studies follow children long enough to observe long-run outcomes and treatment decisions are made by families, raising the possibility that any relationship between medication use and outcomes may reflect family characteristics rather than the causal effect of treatment.

In their recent study Do Stimulant Medications Improve Educational and Behavioral Outcomes for Children with ADHD? (NBER Working Paper 19105), researchers Janet Currie, Mark Stabile, and Lauren E. Jones aim to help fill this gap.

The authors examine the effect of a policy change in Quebec, Canada that greatly expanded insurance coverage for prescription medications. Using data from the National Longitudinal Survey of Canadian Youth, the authors follow a sample of children from 1994 to 2008, enabling them to observe long-term educational outcomes. Their data includes an assessment of ADHD symptoms for all respondents, avoiding the issue that some types of children may be more likely to have been diagnosed with ADHD, as well as information on medication use at each survey wave until the children are 15 years old.

The policy change is a 1997 law that made prescription drug insurance coverage mandatory in Quebec. The law established a public plan for those without drug insurance, with premiums scaled according to income and collected with the provincial income tax to ensure compliance. The enactment of the law led to a rapid increase in drug coverage, from 55 percent of the population in 1996 to 84 percent in 1998, rising to 89 percent by 2003. In the rest of Canada, by contrast, drug coverage rose more slowly and gradually, from 65 percent in 1996 to 76 percent in 2003.

The authors first examine whether the policy change led to an increase in the use of stimulant medication (Ritalin) in Quebec, relative to the rest of Canada. Naturally, medication use may have risen in the rest of Canada during this time as well, due to the gradual spread of insurance or greater acceptance of this treatment. Therefore, the authors use a triple difference specification that focuses on those children most likely to benefit from increased stimulant use in response to the policy change: those with the worst initial ADHD symptoms.

The authors find that the law increased the use of Ritalin in Quebec by 1.15 percentage points for a child with an average level of ADHD symptoms and by even more for children with more severe symptoms. Since the baseline use of Ritalin in the sample is about 2 percent, this represents a reasonably large effect.

Next, the authors turn to exploring the effect of the law and resulting increase in medication use on other outcomes. They find that behavioral outcomes are negatively affected in the medium run, as the law is associated with an increase in the probability of grade repetition, lower math scores, and a deterioration in relationships with parents.

Finally, the authors explore the long-term effects of the policy. Consistent with the medium-term findings, the policy is associated with an increased probability of suffering from depression and a decreased probability of post-secondary education in girls. The authors employ a number of checks to verify that their results are not driven by greater access to drugs to treat physical health conditions, other contemporaneous policy changes, or chance.

In short, the evidence suggests that the increased access to stimulant medication that resulted from Quebec's insurance law had some negative effects on behavioral outcomes, consistent with known side effects, and did not improve academic outcomes. The authors suggest that one possible explanation for this surprising finding is that "medication is a substitute for other types of cognitive and behavioral interventions that might be necessary to help the child learn. By making children less disruptive, ADHD medication could decrease the attention that they receive in the average classroom and reduce the probability of receiving other services."

The authors caution that their study "does not shed light on the question of whether optimal medication use would be beneficial." Many children in their sample appear to take medication in a haphazard manner and the dose taken may not be calibrated to achieve optimal results. "What our results do speak to is the effect of a large increase in the use of ADHD medications in a community, given the usual standard of care available to Quebec children. In Quebec, as in the U.S., any doctor can prescribe Ritalin, and it is not necessary to have expertise treating ADHD. Hence it is not surprising that some use is sub-optimal. Our results suggest that observers of the large increases in the use of medication for ADHD in the U.S. are right to be concerned."

The authors acknowledge funding from the Canadian Institutes of Health Research.

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