Stimulant drugs were the first class of compounds reported as being effective in treating the behavioral disturbances that are evident in children with ADHD (Table 4–1). Stimulants are sympathomimetic drugs structurally similar to endogenous catecholamines. The most commonly used compounds in this class are methylphenidate (Ritalin), d-methylphenidate (Focalin), d-amphetamine (Dexedrine), and a mixed amphetamine product (Adderall). These drugs have been shown to enhance dopaminergic and noradrenergic neurotransmission (Bymaster et al. 2002; Volkow et al. 2001). Because the various stimulants have somewhat different mechanisms of action, some patients may respond preferentially to one or another agent (Greenhill et al. 1998).