n. an atypical antipsychotic used for the treatment of acute mania, schizophrenia, and other psychotic disorders in adults. It is closely related to clozapine but lacks the latter drug’s association with agranulocytosis. Common side effects are sedation, lethargy, weight gain, and orthostatic hypotension. Rarely, like all antipsychotics, it may be associated with tardive dyskinesia or neuroleptic malignant syndrome. U.S. trade names: Zydis; Zyprexa.