Cetirizine, sold under the brand name Zyrtec among others, is a second-generation antihistamine used to treat allergic rhinitis (hay fever), dermatitis, and urticaria. It is taken by mouth. Effects generally begin within an hour and last for about a day. The degree of benefit is similar to other antihistamines such as diphenhydramine.It was patented in 1981 and came into medical use in 1987. It is available as a generic medication. In 2017, it was the 66th most commonly prescribed medication in the United States, with more than eleven million prescriptions.