Methylphenidate (C14H19NO2), or MPH, is an amphetamine-like prescription stimulant commonly used to treat Attention Deficit Hyperactivity Disorder (ADHD) in children and adults. It is also one of the primary drugs used to treat the daytime drowsiness symptoms of narcolepsy. Novartis Pharmaceuticals markets methylphenidate under the brand name Ritalin®.
Methylphenidate was patented in 1950 by the CIBA-Geigy Pharmaceutical Company, a precursor to Novartis, and was initially prescribed as a treatment for depression, chronic fatigue, and narcolepsy, among other ailments. Beginning in the 1960s, it was used to treat children with ADHD, known at the time as hyperactivity or minimal brain dysfunction (MBD). Today MPH is the medication most commmonly prescribed to treat ADHD around the world. According to most estimates, more than 75 percent of MPH prescriptions are written for children, with boys being about four times as likely to take MPH as girls. Production and prescription of MPH rose significantly in the 1990s, especially in the United States, as the ADHD diagnosis came to be better understood and more generally accepted within the medical and mental health communities.
Methylphenidate is a central nervous system (CNS) stimulant. It has a "calming" effect on many children who have ADHD, reducing impulsive behavior and the tendency to "act out", and helps them concentrate on schoolwork and other tasks. Adults who have ADHD often find that MPH increases their ability to focus on tasks and organize their lives.
The means by which methylphenidate helps people with ADHD are not well understood. Some researchers have theorized that ADHD is caused by a dopamine imbalance in the brains of sufferers. MPH is a dopamine reuptake inhibitor, which means that it increases the level of the dopamine neurotransmitter in the brain by partially blocking the transporters that remove it from the synapses. 
In the United States, methylphenidate is classified as a Schedule II narcotic, the designation used for substances that have a recognized medical value but which have a high potential for abuse. Some people abuse MPH by crushing the tablets and snorting or smoking them, which produces a "high" similar to that of cocaine or amphetamine and can lead to addiction. When taken orally in prescribed doses, MPH is not addictive and does not produce a "high".
Treating children with stimulant medication, and methylphenidate in particular, has become controversial as the number of children taking them has increased. Critics contend that MPH is extensively overprescribed in the United States, especially among children; that the drug is used primarily to control or sedate "problem" schoolchildren so that they will not disrupt class; that it transforms healthy children into "zombies", stifling their creativity and intellectual energy; and that it can lead children into dangerous drug addictions later in life. However, the American Medical Association and the U.S. government have found little evidence to support these contentions, and peer-reviewed studies have produced conflicting and inconclusive results. Recent research suggests that ADHD boys who are treated with stimulants like MPH are actually less likely to abuse drugs and alcohol later in life.