Antipsychotic agents are useful in the treatment of psychosis due to both functional disorders (i.e., idiopathic disorders that are usually treated by psychiatrists) and organic mental disorders. These drugs are classified as low- and high-potency agents. Low-potency agents such as chlorpromazine block muscarinic and alpha 1-adrenergic receptors. Consequently, they produce anticholinergic side effects and orthostatic hypotension. High-potency antipsychotic agents have a higher affinity for dopamine receptors and a relatively negligible affinity for muscarinic and alpha 1 receptors. The high-potency agents frequently cause extrapyramidal side effects, such as dystonia and parkinsonism. Serious reactions to antipsychotic drugs include tardive dyskinesia and neuroleptic malignant syndrome.