Cetirizine /sɛˈtɪrᵻziːn/ (trade names Zirtec, Zyrtec, Reactine) 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: for instance they are less likely to induce drowsiness or to interfere with memory formation.