phenothiazine
n. any of a group of chemically related compounds that are mostly used as antipsychotic drugs, having been originally developed as such in the 1950s. Divided into three subgroups—aliphatic, piperazine, and piperidine—the drugs in this class of conventional antipsychotics were the first effective antipsychotic medications and at one time were the most widely used agents for the treatment of schizophrenia. They are also used for the treatment of acute mania, psychotic agitation, and nausea and vomiting, as well as for preanesthesia sedation. It is commonly assumed that their therapeutic effects are produced by blockade of dopamine D2 receptors (see dopamine-receptor antagonist); they also block acetylcholine, histamine, and norepinephrine receptors. A variety of adverse side effects is associated with their use, including extrapyramidal symptoms, tardive dyskinesia, sedation, and anticholinergic effects.