Treating children who have Attention Deficit Hyperactivity Disorder (ADHD) 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.
Prof Pelham said there were "no beneficial effects" of medication and the impact was seemingly negative instead.
"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," he said.
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 examples of just how explosive his behaviour can be.
He has self-harmed, suffers night terrors and is aggressive - he recently assaulted three school teachers.
(Please don't forget that many of the most popular drugs for our kids are basically just smaller doses of drugs we make illegal for adults.)