Used primarily in the treatment of certain heart rhythm disorders, particularly atrial fibrillation and atrial flutter, to restore and maintain normal sinus rhythm. It works by blocking specific cardiac ion channels, prolonging the action potential and refractory period in cardiac tissue. Also employed as an anti-malarial agent in some cases, though less commonly today. In research settings, it serves as a chiral selector in chromatography due to its ability to differentiate enantiomers. Additionally, it has been used off-label to manage leg cramps, although this use is limited due to safety concerns.