http://www.ecanadanow.com/news/health/adhd-drugs-have-no-long-term-benefits-20071112.html Researchers found drugs such as Ritalin and Concerta do work well for short term, but do not offer improvement in a children's behavior after three years.
I'm a little confused, though, about this statement. It sounds like after three years, an unmedicated child is as bad as they were before they were medicated, to which I would respond, well, duh. Drugs like ritalin treat the symptoms, but don't actually fix the underlying causes; just drugging a child (or an adult) to improve symptoms does not mean the behavior while on meds carries over to times where they aren't taking them.