Quinine

Iron Quinine Bitters

From Wikipedia:

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 used for restless legs syndrome, it is not recommended for this purpose due to the risk of side effects. It can be taken by mouth or used intravenously. Malaria resistant to quinine occurs in certain areas of the world. Some quantities are also used in tonic water and give it its bitter taste.