Haloperidol and lithium blocking of the mood response to intravenous methylphenidate

Ten euthymic manic-depressive patients with therapeutic plasma lithium levels were each given two i.v. infusions of 30 mg of methylphenidate. The infusions were separated by at least 3 days. Before one infusion each patient was given 5 mg of haloperidol i.v. and before the other infusion each was given an identical volume of saline. A psychiatric observer was blind to the nature of the pretreatment and the order of pretreatment was randomized. Saline pretreated patients showed marked activation and euphoriant responses despite therapeutic lithium levels. Haloperidol pretreatment reduced this response in three patients and eliminated the euphoriant and activating response in the remaining seven patients. These results agree with the existence of a dopaminergic step in the induction of methylphenidate-induced activation and euphoria.