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.
Most of the estimated 500,000 children in Britain with ADHD receive no treatment at all.
But of those that do, most - about 55,000 last year - are prescribed stimulants like Ritalin and Concerta.
The cost of these drugs to the NHS is about £28m.
In 1999, the American study 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.
But now after longer-term analysis, 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.
"There's no indication that medication's better than nothing in the long run."
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.
And all I can do is go back to the doctors and say: 'Is there anything more you can do?'
Mother of child with ADHD
His mother Sharon said things had gone from bad to worse.
"He has broke down and cried when he gets into situations," she said.
"He says: 'Why am I like this mum, I don't want to feel like this, I don't want to be like this, you know, help me'.
"And all I can do is go back to the doctors and say: 'Is there anything more you can do?'
"All they say is, well, we are doing what we can."
The National Institute for Clinical Excellence is currently revising the treatment guidelines for ADHD.
Chair of the working group Dr Tim Kendall said they were devising a strategy which was likely to involve training for parents as well as "behavioural interventions".
"The important thing is that we have an approach which doesn't focus just on one type of treatment," Dr Kendall said.
Panorama: What Next for Craig? BBC One 8.30pm, Monday 12 November 2007