Early studies suggest that around a third of small children given Ritalin or another ADHD drug have such a bad reaction that they have to stop treatment. Reactions have included sleeplessness, irritability, repetitive behaviour or thoughts, and appetite loss.
The drugs also affect the child's growth. Children on an ADHD drug are around 20 per cent shorter, and 55 per cent lighter, for their age.
(Source: Journal of the American Medical Association, 2007; 298: 1747-9).