Quinine sulfate's primary function is to combat malaria by targeting and destroying the parasites within red blood cells, especially Plasmodium falciparum, which can be resistant to other treatments. While it has been used for leg cramps, this is not its main purpose and is generally discouraged due to potential risks.
Common side effects include cinchonism (tinnitus, headache, nausea, vision problems), gastrointestinal issues, and potential cardiovascular effects. In some cases, it can lead to allergic reactions, blood disorders, low blood sugar, or even serious visual disturbances. Therefore, quinine sulfate should only be used under strict medical supervision.