The action of stimulant medication in attention deficit disorder with hyperactivity: Dopaminergic, noradrenergic, or both?

The effect of methylphenidate (0.3 mg/kg) on the performance of vigilance tasks after a prior treatment with haloperidol (0.04 mg/kg) was investigated to see whether haloperidol changed the response on vigilance tasks. The subjects were 12 attention deficit disorder with hyperactivity boys aged 64 to 122 months. Methylphenidate was shown to diminish attention deficits in the hyperactive group, but when methylphenidate was preceded by haloperidol, this effect was blocked on all the vigilance subtests. The implications of these findings for a primarily dopaminergic action of methylphenidate in attention-disordered children is discussed.