A central nervous system stimulant drug. Methylphenidate (Methylin, Ritalin) is used to treat attention deficit/hyperactivity disorder (ADHD), narcolepsy (sudden attacks of deep sleep), and other conditions. Methylphenidate used to treat ADHD in combination with social, educational, and psychological therapies; the goal is to increase the attention span of a person while decreasing restlessness in children and adults who are hyperactive, impulsive, and easily distracted.