skeletal-muscle–relaxant drug belonging to the alkaloid family of organic compounds. Of botanical origin, it is used in modern medicine primarily as an auxiliary in general anesthesia (anesthetic), frequently with cyclopropane, especially in abdominal surgery. Upon injection, curare acts as a neuromuscular blocking agent to produce flaccidity in striated (striped) muscle (it competes with acetylcholine at the nerve ending, preventing nerve impulses from activating skeletal, or voluntary, muscles). It first affects the muscles of the toes, ears, and eyes, then those of the neck and limbs, and, finally, those involved in respiration. In fatal doses, death is caused by respiratory paralysis.

Crude preparations called curare have been used as arrow poisons (poison) in hunting wild game by the Indians of South America. Sources include various tropical American plants (primarily Chondrodendron species of the family Menispermaceae and Strychnos species of the family Loganiaceae). Crude curare is a resinous, dark brown to black mass with a sticky to hard consistency and an aromatic, tarry odour. The name comes from Indian words (woorari, woorali, urari) meaning “poison.” Preparations have been classified according to the containers used for them: pot curare in earthenware jars, tube curare in bamboo, and calabash curare in gourds.

Several related alkaloidal constituents are responsible for the pharmacological action of these preparations, the principal alkaloid being tubocurarine, first isolated from tube curare in 1897 and obtained in crystalline form in 1935. Tubocurarine chloride (as d-tubocurarine chloride), isolated from the bark and stems of a South American vine (Chondrodendron tomentosum), is the purified form used in medicine.

Injection of curare alkaloids in anesthesia produces a profound relaxation (comparable only to that produced by spinal anesthesia) with a minimal concentration of anesthetic agent. From this there is prompt recovery and a radical reduction of the possibilities of postoperative pneumonias and other complications.

The drug is also employed as a relaxant to keep the throat open, to keep open for examination such hollow organs as the rectum and urethra, to relieve various muscular contractions and convulsions, and to allow manipulations in the lumbar and sacroiliac regions of the back. Because of its quickly reversible action, it is useful in the diagnosis of myasthenia gravis, a muscle disorder. Curare also is used for relief of spastic paralysis, as an adjunct in shock therapy to reduce the incidence of vertebral fractures, and in cases in which a state of profound muscular relaxation or even immobility is desirable.