Quinine is a medication used to treat malaria and babesiosis. This includes the treatment of malaria due to Plasmodium falciparum that is resistant to chloroquine when artesunate is not available. While sometimes used for nocturnal leg cramps, quinine is not recommended for this purpose due to the risk of serious side effects. It can be taken by mouth or intravenously. Malaria resistance to quinine occurs in certain areas of the world. Quinine is also used as an ingredient in tonic water to impart a bitter taste.
Quinine was first isolated in 1820 from the bark of a cinchona tree, which is native to Peru, and its molecular formula was determined by Strecker in 1854. The class of chemical compounds to which it belongs is thus called the cinchona alkaloids. Bark extracts had been used to treat malaria since at least 1632 and it was introduced to Spain as early as 1636 by Jesuit missionaries returning from the New World. It is on the World Health Organization's List of Essential Medicines. Treatment of malaria with quinine marks the first known use of a chemical compound to treat an infectious disease.