Australasian Science: Australia's authority on science since 1938

ADHD Medication Slows Boys’ Growth

By Stephen Luntz

Long-term medication for attention deficit hyperactivity disorder (ADHD) reduces the growth rates of 14–16-year-old boys.

Long-term medication for attention deficit hyperactivity disorder (ADHD) reduces the growth rates of 14–16-year-old boys, says Dr Alison Poulton of the University of Sydney’s Nepean Clinical School in a paper published in the Medical Journal of Australia.

Poulton compared a group of boys treated for ADHD for at least 3 years and found that, once they had reached their early teens, they were significantly shorter than their peers. Moreover, there was a correlation between dosage and growth rate.

While she acknowledges it is possible the condition, rather than the medication, is the reason the treated boys were relatively short, Poulton says the dosage effect makes this unlikely. She adds: “I can’t think of a way to demonstrate this decisively other than to give some boys a placebo for at least 3 years, but it would be unethical to deny an effective treatment for this long and parents would never agree to randomisation determining their child’s long-term treatment”.

Poulton has previously shown that children grow more slowly and lose weight when first put on ADHD medication. Yet puzzlingly, the heights of 12–14-year-olds were not statistically significantly different from the control group. Poulton says she is “not sure about the precise hormonal mechanisms” but notes that the boys taking medication appeared to be experiencing delays in later stages of puberty.

The study did not establish whether medication altered the boys’ final height, but Poulton says one comparison of men treated for ADHD in childhood with their fathers and brothers found no effect. However, she says larger sample sizes might produce statistically significant results.

Given the well-established effects of ADHD medication on appetite and weight, Poulton says the results are unsurprising since “weight gain fuels growth in height”. But she doesn’t think there are necessarily significant detrimental effects in areas such as brain development. Nevertheless, she notes that height is beneficial in areas such as sport, which can affect social inclusion.

“Friends with an earlier growth spurt could quickly overtake boys who are on medication, leaving them socially at quite a dis­advantage,” Poulton says. “One of the effects of puberty is often to become more defiant, and this can manifest in being unwilling to take medication. Not growing as fast could become another reason not to want to take it.

“To maintain an adequate rate of growth during puberty we recommend that boys on ADHD stimulant medication should take the lowest dose that adequately treats their ADHD.”