Cyproximide is a psychoactive drug discovered by American Cyanamid company. The drug exhibited activity as a central nervous system depressant and was claimed to be useful as a tranquilizing agent, hypnotic agent or muscle relaxant. The phenobarbital-like activity of cyproximide after intraperitoneal administration was demonstrated in rod traversal, clinging and righting reflex tests in mice. In addition to CNS depressant activity, cyproximide had a mild stimulant and antidepressant effects, which were shown by the restoration of exploratory behavior and an increase in locomotor activity in mice. Chronic administration of the drug led to a greater incidence of proliferative lesions in the liver of treated rats; however, the incidence of hepatocellular neoplasms was the same in treated and control rats.