Drugs commonly used to treat attention deficit hyperactivity disorder (ADHD) are not effective in the long term, according to new research.
A highly influential study in the US has concluded that while drugs such as Ritalin and Concerta work in the short term, there is no demonstrable improvement in children's behaviour after three years of medication.
The findings, reported on BBC's Panorama programme, also suggested long-term use of the drugs could stunt children's growth.
The Multimodal Treatment Study of Children with ADHD (MTA) has been monitoring the treatment of 600 children across the US since the 1990s. In 1999, it concluded that after one year, medication worked better than behavioural therapy for ADHD.
This finding influenced medical practice on both sides of the Atlantic and prescription rates in the UK have since tripled.
The report's co-author, Professor William Pelham, of the University of Buffalo, said: "I think that we exaggerated the beneficial impact of medication in the first study. We had thought that children medicated longer would have better outcomes. That didn't happen to be the case.
"The children had a substantial decrease in their rate of growth so they weren't growing as much as other kids both in terms of their height and in terms of their weight. And the second was that there were no beneficial effects - none.
"In the short run [medication] will help the child behave better, in the long run it won't. And that information should be made very clear to parents."
Panorama said GPs in the UK prescribed ADHD drugs such as Ritalin and Concerta to around 55,000 children last year - at a cost of £28m to the NHS.
Dr Tim Kendall, of the Royal College of Psychiatrists, who is helping prepare new NHS guidelines for the treatment of ADHD said: "A generous understanding would be to say that doctors have reached the point where they don't know what else to offer."
