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. How it works Ritalin improves the activity of certain parts of the brain which are under-active.