Treating children who have Attention Deficit Hyperactivity Disorder with drugs is not effective in the long-term, research has shown.
A study obtained by the BBC's Panorama programme says drugs such as Ritalin and Concerta work no better than therapy after three years of treatment.
The findings by an influential US study also suggested long-term use of the drugs could stunt children's growth.
It said that the benefits of drugs had previously been exaggerated.
The Multimodal Treatment Study of Children with ADHD 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."
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.
The Panorama programme features disturbing footage of a 14-year-old from Stoke-on-Trent, who has been on ADHD medication for a decade.
Craig Buxton's family kept a video diary of his behaviour and captured on camera disturbing examples of just how explosive his behaviour can be - he recently assaulted three school teachers. ( BBC )