Ritalin (methylphenidate) is a central nervous system stimulant primarily prescribed to treat attention-deficit hyperactivity disorder (ADHD) and narcolepsy in the United States. It works by increasing levels of dopamine and norepinephrine in the brain, helping to improve attention, focus, and impulse control. Often prescribed for both children and adults, it is a commonly used treatment for managing the symptoms of ADHD, although it can sometimes cause side effects like insomnia, loss of appetite, and anxiety.