Researchers claim to have further evidence that attention deficit hyperactivity disorder medication can delay growth in teenage boys.
A study from the University of Sydney, to be published in the Medical Journal of Australia today, found that adolescent boys with ADHD were more likely to be slimmer and shorter than other boys their age.
Researchers studied 65 boys aged between 12 and 16 who had been on stimulant medication for more than three years and found prolonged treatment of methylphenidate - commonly known as Ritalin - or dexamphetamine was associated with a slower rate of physical development during puberty.
Boys aged 12 to 14 showed significantly lower weight and body mass index and those aged between 14 and 16 had significantly lower weight and height.
There was no difference in pubertal development in the 12 to 14-year-olds but those aged between 14 and 16 showed "significant delay" compared with their peers, which researchers warned could have social implications.
"These findings suggest that stimulant medication delays the rate of maturation during puberty, but not the onset of puberty," research study author Dr Alison Poulton said.
The authors recommended that to maintain an adequate growth rate, boys on ADHD medication should take the lowest dose compatible with their treatment.
Ritalin was the "drug of first choice" for 78 per cent of those surveyed, while dexamphetamine was prescribed for 22 per cent.
The study backs a 2007 US report, which found ADHD drugs slowed children's rate of growth.
The latest research also suggests that the impact on growth reached its maximum after three years.
Michele Toner, from the Learning and Attentional Disorders Society of WA, agreed with the authors that further research was needed to establish whether differences in development were because of ADHD or the treatment. "ADHD is a complicated condition. There can be serious consequences if it is left untreated, including significant academic, social and personal challenges," Dr Toner said.
Retiring Labor MP Martin Whitely, who has campaigned against the medication, said he was not surprised by the findings.
"All the evidence shows that in the long term, ADHD drugs are associated with all sorts of negative outcomes," he said.