Amphetamines that are approved for use for the treatment of narcolepsy include dextroamphetamine, racemic amphetamine, and various combinations of D-amphetamine and racemic amphetamine. Methylphenidate is a central psychostimulant that is approved for the treatment of narcolepsy, and that is also used for other causes of excessive daytime sleepiness (EDS). Despite the abuse liability of amphetamine, dextroamphetamine and methamphetamine, all three agents are effective for the treatment of EDS of central origin. Amphetamine and methamphetamine are well absorbed from the gastrointestinal tract and are primarily metabolized through hepatic enzymatic pathways. At excessive dosages, amphetamines and methylphenidate can lead to irritability, paranoia, aggressive behavior, hyperpyrexia, arrhythmias, rhabdomyalysis, renal failure, coronary and cerebral vasospasm, cardiovascular collapse, and death. Several studies have been conducted in an effort to evaluate the potential for methamphetamine to produce dopamine neurotoxicity in humans, by measuring the dopamine transporter (DAT).