Terfenadine is primarily known for its application as an antihistamine, used to alleviate symptoms associated with allergies, such as hay fever, hives, and other allergic skin conditions. It works by blocking the effects of histamine, a substance in the body that causes allergic symptoms. Due to its non-sedative properties, it was particularly favored for treating allergies without causing drowsiness, making it suitable for individuals who needed to remain alert during daily activities. However, its use has been largely discontinued in many countries due to the risk of serious heart-related side effects, particularly when interacting with certain medications or in individuals with pre-existing heart conditions. Despite this, its development marked a significant advancement in antihistamine therapy, paving the way for safer alternatives.