After those first three years, ADHD can be just as successfully treated with behavioural therapy.
The Multimodel Treatment Study has been monitoring the health of 600 young people with ADHD since the early 1990s.
In addition to discovering the short-term benefits of drugs such as Ritalin and Concerta, the study has discovered that the drugs could also stunt children's growth.
Ironically, it was the initial findings of the same study that sparked much of the growth in ADHD drug sales. In 1999, the study concluded that the drugs worked better than therapy over the first year.
Prof William Pelham, one of the study's co-authors, 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."
(Source: BBC Panorama, November 12, 2007).