Quinine sulfate is a medication derived from the bark of the cinchona tree. It is primarily used to treat malaria, a disease caused by parasites transmitted through mosquito bites. Quinine works by interfering with the parasites' ability to reproduce and survive in the bloodstream. In addition to its use in treating malaria, quinine sulfate has also been used to relieve leg cramps. However, its use for this purpose is less common today due to potential side effects. Quinine is also known for its bitter taste and is an ingredient in tonic water, which is often mixed with gin.