widely used anthelmintic (worming agent) in veterinary medicine. Phenothiazine is an organic compound effective against a broad range of parasites in cattle, horses, poultry, sheep, and swine. A highly toxic drug, it is not recommended for human use and is not effective in dogs or cats.

Some of the most useful antipsychotic drugs are derivatives of phenothiazine. They are widely used to treat the symptoms of persons suffering from schizophrenia, psychotic depression, the manic phase of manic-depression, and organic psychoses. The phenothiazines suppress or eliminate such symptoms as hallucinations, delusions, agitation, and disordered thinking. The drugs apparently achieve their tranquillizing effect by blocking the transmission of dopamine in the brain. Among the most widely used phenothiazines are chlorpromazine (marketed under Thorazine and other trade names), thioridazine (Mellaril), and trifluoperazine (Stelazine).