The drug Ritalin was originally used as a stimulant for adults - until researchers discovered it could help children concentrate. It's now taken by millions of patients around the world to treat Attention Deficit Hyperactivity Disorder or ADHD. Witness speaks to Dr C Keith Conners, one of the researchers behind the first randomised clinical trial of Ritalin on children in 1964. PICTURE: Ritalin blister-packs and packet. Ritalin is a proprietary brand of Novartis Pharmaceuticals. Copyright Science Photo Library.