Consistent use of ADHD medication may stunt growth by 2 inches, large study finds

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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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