The third-generation antihistamine levocetirizine, marketed as Xyzal, is used for the treatment of allergic rhinitis and hives of unknown cause. Compared to older antihistamines, it is less sedating. The drug works by blocking an allergic reaction-triggering chemical (histamine). There is no evidence to suggest levocetirizine prevents or treats hives, anaphylaxis, or other severe allergies.