Used to treat malaria, particularly caused by Plasmodium falciparum when chloroquine is not effective. It works by interfering with the parasite's ability to break down hemoglobin in red blood cells, leading to toxic buildup that kills the parasite. Also used off-label for nocturnal leg cramps, though this use is limited due to risk of side effects. Serves as a bittering agent in beverages like tonic water, giving them a characteristic bitter taste. Used in research and analytical chemistry as a fluorescence standard due to its strong and stable fluorescent properties.