Curare is a group of chemically similar alkaloid toxins derived from plants. Since ancient times, it has been used by the aboriginal people of Central and South America as a coating for poison darts and arrows. It irreversibly inhibits acetylcholine receptors resulting in paralysis of the diaphragm and asphyxiation. Although it can be lethal if injected, it can be safely ingested as the normal process of digestion quickly breaks down the toxin.
In medicine, curare was developed as an anesthetic until it was found that although it paralyzed the patient, it did not deaden pain. It was later used as a muscle relaxant during surgery as a combination of anesthetic and curare would prevent reflex muscle movements that could only be achieved through a higher, more dangerous dose of anethetic.
Curare is rarely used in modern medicine as rocuronium bromide and pancuronium bromide are much safer alternatives.