Used primarily to treat certain types of irregular heart rhythms (arrhythmias), particularly atrial fibrillation and atrial flutter. It works by affecting the electrical activity of the heart, specifically by inhibiting sodium and potassium ion channels in cardiac muscle cells, to help maintain a normal rhythm. Also used in the management of malaria when other treatments are not effective, due to its antimalarial properties. In research settings, it serves as a chiral selector in chromatography for separating enantiomers. It has been used in the diagnosis and treatment of Brugada syndrome, a condition involving abnormal heart rhythms, but with caution due to the risk of inducing severe arrhythmias. Additionally, it has been used off-label to treat leg cramps, although this use is limited due to safety concerns.