Used primarily as a long-acting, non-sedating antihistamine for the treatment of allergic conditions such as hay fever, chronic urticaria, and other allergic skin reactions. It works by blocking histamine H1 receptors, reducing symptoms like sneezing, itching, and runny nose. Due to risk of cardiac side effects, including QT prolongation and arrhythmias, its use has been discontinued or restricted in many countries. Was commonly taken orally in tablet form for 24-hour relief. Not recommended for use with certain medications that affect heart rhythm or liver metabolism.