Quinine hydrochloride dihydrate is primarily used as an antimalarial medication, effectively treating malaria caused by Plasmodium falciparum and other Plasmodium species. It is particularly valuable in regions where malaria is resistant to other treatments. Additionally, it is employed to manage nocturnal leg cramps, though this use is less common due to potential side effects. In some cases, it serves as a bittering agent in tonic water, contributing to its distinctive flavor. Its application extends to research settings, where it is utilized in biochemical studies to investigate its mechanisms of action and potential therapeutic benefits.