Xyzal is a third-generation non-sedative antihistamine indicated for the relief of symptoms associated with seasonal and perennial allergic rhinitis and uncomplicated skin manifestations of chronic idiopathic urticaria. It was developed from the second-generation antihistamine cetirizine. Xyzal is the R-enantiomer of the cetirizine racemate. Xyzal is an inverse agonist that decreases activity at histamine H1 receptors. This in turn prevents the release of other allergy chemicals and increased blood supply to the area, and provides relief from the typical symptoms of hay fever. It does not prevent the actual release of histamine from mast cells. Xyzal was approved by the United States Food and Drug Administration on May 25, 2007 and is marketed under the brand XYZAL® by sanofi-aventis U.S. LLC .