Ritalin (methylphenidate) is a central nervous system (CNS) stimulant. It has effects similar to, but more potent than, caffeine and less potent than amphetamines. The way Ritalin works in a user is not completely understood. What is known about how Ritalin"works" is that it produces malfunctions in the brain rather than by improving brain function. This is the only way it works.

Ritalin is available as 5, 10, and 20 mg tablets for oral administration. A 20 mg extended-release tablet for oral administration is also available. Methylphenidate hydrochloride (the chemicals that make up Ritalin) is a white, odorless, fine crystalline powder.

This medication is often prescribed for children who are believed to have attention-deficit hyperactivity disorder (ADHD). Ironically, there is no fool proof method to determine whether a person has ADHD. Additionally, in 1998 at the National Institutes of Health Consensus on ADHD, the following statement was issued: "We do not have an independent, valid test for ADHD, and there is no data to indicate that ADHD is due to a brain malfunction".

Because stimulant medicines such as Ritalin have such a high potential for abuse, the U.S. Drug Enforcement Administration (DEA) has placed tight, Schedule II controls on their manufacture, distribution, and prescription. For example, the DEA requires special licenses for these activities, and prescription refills are not allowed. Also, each state may impose further regulations and restrictions, such as limiting the number of dosage units per prescription.