The overdiagnosing of ADHD may be related to the way health insurance is paid and the self-interest of doctors who gain fees from patients they write such prescriptions for. There is still a strong tendency only to respect as illness that which is physiological and can be described physiologically. A child who has no abnormality or disease can go to a psychiatrist, be said to have ADHD, and be put on Ritalin. The psychiatrist will get his fee, the insurance company will pay the bill. There will of course be a series of visits to the psychiatrists.
Drug companies benefit enormously too.
It is a mild stimulant which works by activating the brain stem arousal system and cortex. We do not know that the former is abnormal at all, but we do know that Ritalin will calm people down and allow them to pay attention to something for longer spans of time than is normal for them without Ritalin. There is also some evidence that Ritalin does not restore any chemical imbalance having to do with glucose at all. Not only are there no tests to prove that Ritalin is generally effective for children who are hyperactive, but there is no evidence that the use of Ritalin actually gets rid the problems such children have in school. Consider the following study.