Human

Cetirizine dihydrochloride  is a second-generation antihistamine used in the treatment of hay fever, allergies, angioedema, and urticaria. It is a major metabolite of hydroxyzine, and a racemic selective H₁ receptor antagonist. Second-generation antihistamines like cetirizine are less able to cross the blood–brain barrier and therefore have diminished effects on the central nervous system compared to first-generation drugs.