antiparkinsonian drug
any pharmacological agent that reduces the severity of symptoms of Parkinson’s disease or drug-induced parkinsonism (common with the use of conventional antipsychotics), including tremors, movement and gait abnormalities, and muscle rigidity. Such agents include antihistamines (e.g., diphenhydramine), anticholinergic drugs (e.g., benztropine, trihexyphenidyl), dopamine-receptor agonists (e.g., carbidopa, levodopa), and specific enzyme inhibitors of catechol-O-methyltransferase (COMT) and of MAO-B (see monoamine oxidase).