Fexofenadine, sold under the brand name Allegra among others, is an antihistamine pharmaceutical drug used in the treatment of allergy symptoms, such as hay fever and urticaria. Therapeutically, fexofenadine is a selective peripheral H1 blocker. It is classified as a second-generation antihistamine because it is less able to pass the blood–brain barrier and cause sedation, compared to first-generation antihistamines. It was patented in 1979 and came into medical use in 1996. It is on the World Health Organization's List of Essential Medicines. Fexofenadine has been manufactured in generic form since 2011. In 2020, it was the 255th most commonly prescribed medication in the United States, with more than 1million prescriptions. Medical uses Fexofenadine is used for relief from physical symptoms associated with seasonal allergic rhinitis and for treatment of chronic urticaria. It does not cure, but rather prevents the aggravation of allergic rhinitis and chronic idiopathic urticaria, and reduces the severity of the symptoms associated with those conditions, providing relief from repeated sneezing, runny nose, itchy eyes or skin, and general body fatigue. In a 2018 review, fexofenadine, along with levocetirizine, desloratadine, and cetirizine, was cited to be a safe to use for individuals with inherited long QT syndrome. Efficacy For the treatment of allergic rhinitis, fexofenadine is similarly effective to cetirizine, but is associated with less drowsiness than cetirizine. Fexofenadine was also shown to inhibit histamine-induced wheal and flare to a significantly greater degree than loratadine or desloratadine, but was slightly less effective than levocetirizine. Fexofenadine at doses above 120 mg a day does not appear to provide additional efficacy in the treatment of allergic rhinitis. Side effects The most common side effects include headache, back and muscle pain, miosis or pinpoint pupils, nausea, drowsiness, and menstrual cramps. Anxiety and insomnia have also been rarely reported. The most common side effects demonstrated during clinical trials were cough, upper respiratory tract infection, fever, and otitis media for children ages 6 to 11 and fatigue for children ages 6 months to 5 years. Overdose The safety profile of fexofenadine is quite favorable, as no cardiovascular or sedative effects have been shown to occur even when taking 10 times the recommended dose. Research on humans ranges from a single 800-mg dose, to a twice-daily, 690-mg dose for a month, with no clinically significant adverse effects, when compared to a placebo. No deaths occurred in testing on mice, at 5000 mg/kg body weight,