Buy Ritalin Online. To treat ‘Attention Deficit Hyperactivity Disorder’ (ADHD). It is used in children and young people between the ages of 6 and 18. It is used only after trying treatments which do not involve medicines. Such as counselling and behavioural therapy. Ritalin is not for use as a treatment for ADHD in children under 6 years of age or in adults. It is not known if it is safe or of benefit in these people.