Allegra 120 mg is an antihistamine medication used to relieve symptoms of allergic rhinitis such as sneezing, runny nose, itchy or watery eyes, and nasal congestion. It contains the active ingredient Fexofenadine Hydrochloride, which helps block histamine, a substance in the body that causes allergy symptoms. Allegra 120 mg starts working within an hour and provides relief for up to 24 hours.