[fee-nuh-thahy-uh-zeen, -zin]
phenothiazine, any one of a class of drugs used to control mental disorders. Phenothiazines, along with other antipsychotic, or neuroleptic, drugs are used for such disorders as schizophrenia, paranoia, mania, psychosis resulting from mental deficiency, some forms of senility, hyperactivity in children, and even severe anxiety. Phenothiazines reduce psychiatric disorders without causing addiction or euphoria; sedation usually only occurs in the early stages of drug therapy. The most widely used phenothiazine, chlorpromazine (Thorazine), is prescribed for overactive schizophrenics; trifluoperazine (Stelazine) is used for inhibited and withdrawn schizophrenics. Typically, when a phenothiazine is taken over long periods of time, the frequency of recurring schizophrenic episodes decreases. Other phenothiazines are used in anesthesia and to control itching. Although many patients on phenothiazines and other neuroleptics show marked improvement, these drugs, when used over long periods of time, are fairly toxic. Parkinsonism (see Parkinson's disease) is a well-known side effect. Some patients experience severe reduction of motor activity, abnormal skin pigmentation, and visual impairment. Chlorpromazine therapy is associated with jaundice. Because many phenothiazines are potent anti-emetics, i.e., they control vomiting, they may mask symptoms of toxic drug overdosage or of pathological disorders such as brain tumors. Phenothiazines also cause a disorder called tardive dyskinesia, which consists of bizarre muscular movements such as lip smacking and abnormal postures. It occurs in patients who have been given the drug for long periods of time. See also psychopharmacology.

Phenothiazine is the organic compound with the formula S(C6H4)2NH. This yellow tricyclic compound is soluble in acetic acid, benzene, and ether. The compound is related the thiazine-class of heterocyclic compounds. Derivatives of the parent compound find wide use as drugs.


The compound was originally prepared by Bernthsen in 1883 via the reaction of diphenylamine with sulfur, but more recent syntheses rely on the cyclization of 2-substituted diphenylsulfide. The pharmaceutically-significant derivatives of phenothiazine are not prepared from phenothiazine.

Non-drug applications

The synthetic dye methylene blue, containing the structure, was described in 1876. Phenothiazine itself was introduced by DuPont as an insecticide in 1935. It is sometimes used as an antihelminthic in livestock.

Phenothiazine-derived drugs

The phenothiazine structure occurs in various neuroleptic drugs, e.g. Chlorpromazine, and antihistaminic drugs, e.g. Promethazine. The term "phenothiazines" describes the largest of the five main classes of neuroleptic antipsychotic drugs. These drugs have antipsychotic and, often, antiemetic properties, although they may also cause severe side effects such as akathisia, tardive dyskinesia, extrapyramidal symptoms, and the rare but potentially fatal neuroleptic malignant syndrome as well as substantial weight gain.

Phenothiazines are used as inodilators in congestive heart failure, acting upon the type I calcium/calmodulin dependent phosphodiesterase.

Phenothiazine antipsychotics are classified into three groups that differ with respect to the substituent on nitrogen: the aliphatic compounds (bearing acyclic groups), the "piperidines" (bearing piperidine-derived groups), and the piperazine (bearing piperazine-derived substituents).

Group Autonomic Example Sedative Extrapyramidal side-effect
Aliphatic compounds
moderate Chlorpromazine (marketed as Thorazine, Chlor-PZ, Klorazine, Promachlor, Promapar, Sonazine, Chlorprom, Chlor-Promanyl, Largactil) strong moderate
Promazine (trade name Sparine) moderate moderate
Triflupromazine (trade names Stelazine, Clinazine, Novaflurazine, Pentazine, Terfluzine, Triflurin, Vesprin) strong moderate/strong
Levomepromazine in Germany and Methotrimeprazine in America (trade names Nozinan, Levoprome) extremely strong low
Piperidines strong Mesoridazine (trade name Serentil) strong weak
Thioridazine (trade names Mellaril, Novoridazine, Thioril) strong weak
Piperazines weak Fluphenazine (trade names Prolixin, Permitil, Modecate, Moditen) weak/moderate strong
Perphenazine (sold as Trilafon, Etrafon, Triavil, Phenazine) weak/moderate strong
Flupentixol (sold as Depixol, Fluanxol) moderate strong
Prochlorperazine (trade names Compazine, Stemetil)
Trifluoperazine (trade name Stelazine) moderate strong


Further reading

Appendix: tradenames for phenothiazine

Like many commercially significant compounds, phenothiazine has numerous trade names including AFI-Tiazin; Agrazine; Antiverm; Biverm; Dibenzothiazine; Orimon; Lethelmin; Souframine; Nemazene; Vermitin; Padophene; Fenoverm; Fentiazine; Contaverm; Fenothiazine; Phenovarm; Ieeno; ENT 38; Helmetina; Helmetine, Penthazine; XL-50; Wurm-thional; Phenegic; Phenovis; Phenoxur; Reconox.

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