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The Multimodal Treatment Study of ADHD (MTA Study) is the largest ADHD treatment study ever conducted — nearly 600 7–9-year-old children with ADHD were randomly assigned to one of four interventions:

1) Carefully monitored medication treatment;

2) Intensive behavior therapy;

3) Medication Treatment combined with Behavior Therapy; or

4) Community Care (parents obtained whatever treatment they desired).

After 14 months, results indicated that children receiving carefully monitored medication treatment or medication treatment plus intensive behavior therapy had lower levels of ADHD symptoms and somewhat better overall adjustment compared to those receiving intensive behavioral treatment alone or regular community care.

Ten months after study treated had ended, children who had received intensive medication treatment — either alone or in combination with behavior therapy — were still doing better than those who received intensive behavior therapy only or community care. The magnitude of the relative benefits, however, had been reduced by about 50% compared tot the initial outcome assessment. And, when participants were assessed again a year later, no group differences based on initial treatment assignments were found; the same was true when participants were evaluated again several years later during adolescence. Thus, the initial benefits associated with carefully monitored medication treatment had evaporated; this is not surprising given that many participants had stopped taking medication and the care with which this treatment was provided during the treatment phase of the study was no longer available.

The researchers continued to follow the sample annually through age 18 and then on a reduced schedule to age 25. During the annual assessments, information on treatments received in the prior year was obtained; participants were considered to have received medication treatment if they had taken the equivalent of at least 10 mg of methylphenidate on at least half the days during the year. Based on this annual medication use data through age 18, 3 medication use groups were formed:

a) Consistent, i.e,. those who had met the minimum threshold during each year;

b) Inconsistent, i.e., those meeting the minimum threshold in some but not all years; and

c) Negligible, i.e., below the minimum threshold in all years.

The Latest Results

At the most recent follow-up assessment when participants were 25, self- and parent-reported ADHD symptoms were obtained. In addition, the researchers measured participants’ height. This data was also collected on a group of comparably aged young adults from the same communities who had not been diagnosed with ADHD in childhood, i.e., comparison subjects.

Consistency of medication use — Only 14.3% of participants used medication consistently through age 18; remember, this does not reflect optimal medication treatment but only that a minimum threshold was met each year. Twenty-three percent had not met this threshold in any year and the remaining 69% were in the Inconsistent use group, with the threshold met for some years but not others.

Persistence of symptoms — Relative to comparison subjects, participants with ADHD maintained substantially higher ADHD symptoms over time based on the average of their self-report and their parents’ report. The magnitude of this difference was large and indicates substantial persistence of ADHD symptoms into young adulthood. Symptoms reported by parents were significantly higher than symptoms reported by participants themselves.

Are ADHD symptoms in young adulthood related to patterns of medication use through adolescence? The clear answer to this question was NO. Regardless of whether participants were Consistent, Inconsistent, or Negligible users of ADHD medication through adolescence, their self- and parent-reported ADHD symptoms were quite similar. There was thus no indication that consistent medication treatment over a number of years had any persistent impact.

Is there an association between persistent medication use and adult height? — This association was found. Students in the Consistent and Inconsistent medication treatment groups had average heights — combined across these groups — that were about an inch shorter than those in the Negligible treatment group. And, participants in the Consistent Group were nearly an inch shorter on average than those in the Inconsistent group, i.e., nearly 2 inches shorter than those in the Negligible group.

Conclusions

Three broad conclusions can be drawn from this study.

First, there was substantial persistence of ADHD symptoms into adulthood. Although not mean youth with ADHD continue to struggle with ADHD as adults, this is not a condition that most children simply outgrow. Rather, it is likely to be a chronic condition that must be managed effectively over time. Keeping effective treatment in place over many years, while extremely challenging, may often be necessary.

Second, although the benefits of medication treatment on ADHD symptoms dissipate, the impact on adult stature persists. Consistent medication treatment through adolescence was not linked to reduced symptoms in young adulthood; unfortunately, however, it was associated with reduced adult height . The impact on height was not trivial, with average differences between Consistent and Negligible medication treatment groups of roughly 2 inches. One implication of this finding is that reducing medication dose, which can be done when medication is combined with behavior therapy, could be an effective way to mitigate adverse height outcomes.

While these are interesting and important findings, caution is required in drawing certain conclusions. It would be erroneous to conclude that medication treatment has no long-term benefits as only core ADHD symptoms were examined. It remains possible that benefits on other important outcomes not examined here, e.g., educational attainment, work history, etc., were associated with consistent medication treatment. It is also true that medication treatment after the 14-month treatment portion of the study ended was no longer managed and monitored as it had been.

These data also provide don’t address whether adults who continued to take medication were benefiting from it. The findings reported here highlight that enduring medication benefits should not be expected; instead, whatever benefits this treatment provides while in place will likely dissipate when it stops.

Finally, while it is tempting to conclude that stimulant medication treatment was the cause of reduced adult stature, the design of the study does not fully allow support this conclusion. It is possible that some other factor that contributed to some participants taking medication more consistently, e.g., more severe symptoms, also explains the reduced height attainment in this group.

Take-Home Message

These limitations and uncertainties not withstanding, several ‘take home’ messages are important.

First, relatively few youth with ADHD use medication consistently over their development, even though it is the treatment that currently has the strongest empirical support for reducing symptoms.

Second, many with ADHD will continue to struggle with ADHD symptoms into adulthood, even though some show significant reductions in core symptoms over time.

Third, although medication helps control symptoms in the short-term, it is not a cure. Even long-term treatment provided in community settings does not seem to yield persistent benefits on core symptoms.

Fourth, we don’t know whether optimal medication treatment maintained over many years would have a greater impact. Unfortunately, the study required to answer this question will probably never be done.

Finally, parents and clinicians need to balance the need for persistent treatment in some children with the likely consequences of reduced adult height. Whether or not this is an important concern may depend on the height a child would have otherwise attained.

Because height reduction would likely be linked to cumulative exposure to stimulant medication over time, working to find the lowest effective dose is a good practice. In many cases, this can be achieved by combining medication treatment with other behavior therapy and/or other approaches.

– Dr. David Rabiner is a child clinical psychologist and Director of Undergraduate Studies in the Department of Psychology and Neuroscience at Duke University. He publishes the Attention Research Update, an online newsletter that helps parents, professionals, and educators keep up with the latest research on ADHD.

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