Phenothiazine, the parent compound of a multitude of present-day drugs, has been employed on an extensive scale for its insecticidal, fungicidal, antibacterial and anthelmintic properties. Phenothiazine was formerly used as an insecticide and as a drug to treat infections with parasitic worms (antihelminthic) in livestock and people. It was introduced as antihelminthic in livestock in 1940 and is considered, with thiabendazole, to be the first modern antihelminthic. Almost a catholicon, its widespread use in animals and man has led to the uncovering of many adverse reactions encompassing effects on blood elements, neuromuscular problems and photosensitization. Its potential side effects have now limited its use. The chemical structure of phenothiazine provides a most valuable molecular template for the development of agents able to interact with a wide variety of biological processes. Synthetic phenothiazines (with aliphatic, methylpiperazine, piperazine-ethanol, piperazine-ethyl, or piperidine side-chain) and/or phenothiazine-derived agents e.g., thioxanthenes, benzepines, imonostilbenes, tricyclic antidepressants, dimetothiazine, and cyproheptadine have been effective in the treatment of a number of medical conditions with widely different etiology. These include various currently clinically used drugs for their significant antihistamic, antipsychotic, anticholinergic (antiparkinson), antipruritic, and/or antiemetic properties.

Trimeprazine (also known as Alimemazine), a phenothiazine used as antipsychotic drug. This drug is used in Russia under brand name TERALIGEN and has anti-histamine, sedative, and anti-emetic (anti-nausea) effects. Teraligen is used to treat neurosis, depression and anxiety of different origins. It prevents and relieves allergic conditions, which cause pruritus and urticaria by blocking histamine produced by the body during an allergic reaction. Trimeprazine competes with free histamine for binding at HA-receptor sites. This antagonizes the effects of histamine on HA-receptors, leading to a reduction of the negative symptoms brought on by histamine HA-receptor binding. Trimeprazine is not approved for use in humans in the United States. Nevertheless, combination of alimemazine and prednisolone (commonly sold under the brand name Temaril-P) is licensed as an antipruritic and antitussive in dogs.

Trimeprazine (also known as Alimemazine), a phenothiazine used as antipsychotic drug. This drug is used in Russia under brand name TERALIGEN and has anti-histamine, sedative, and anti-emetic (anti-nausea) effects. Teraligen is used to treat neurosis, depression and anxiety of different origins. It prevents and relieves allergic conditions, which cause pruritus and urticaria by blocking histamine produced by the body during an allergic reaction. Trimeprazine competes with free histamine for binding at HA-receptor sites. This antagonizes the effects of histamine on HA-receptors, leading to a reduction of the negative symptoms brought on by histamine HA-receptor binding. Trimeprazine is not approved for use in humans in the United States. Nevertheless, combination of alimemazine and prednisolone (commonly sold under the brand name Temaril-P) is licensed as an antipruritic and antitussive in dogs.

Oxomemazine is a histamine H₁-receptor antagonist. Additionally, oxomemazine could be classified as a ligand for M1 receptors. It is used in the symptomatic treatment of non-productive coughs that occur specifically at night.