Quinine

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 restless legs syndrome, 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 the ingredient in tonic water that gives it its bitter taste.

Common side effects include headache, ringing in the ears, trouble seeing, and sweating. More severe side effects include deafness, low blood platelets, and an irregular heartbeat. Use can make one more prone to sunburn. While it is unclear if use during pregnancy causes harm to the baby, treating malaria during pregnancy with quinine when appropriate is still recommended. Quinine is an alkaloid, a naturally occurring chemical compound. How it works as a medicine is not entirely clear.

Quinine was first isolated in 1820 from the bark of a cinchona tree, which is native to Peru. 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 from the New World. Quinine is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system.