Cocaine is a natural product extracted from the leaves of Erythroxylon coca Lam (coca leaves). This tropical shrub is cultivated widely on the Andean ridge in South America and is the only known natural source of cocaine. Normally produced as the hydrochloride salt, it has limited medical use as a topical anaesthetic. The free base, sometimes known as crack, is a smokable form of cocaine. Coca leaves have been used as a stimulant by some indigenous people of South America since historical times. Purified cocaine has been misused as a central nervous system stimulant since the early years of the twentieth century. Cocaine is under international control.