Diarrhea and coughing have also been observed in children. Cetirizine, the active ingredient of Zyrtec, is a second-generation antihistamine that blocks the action of histamine (a product of the ...

and often cough.” By blocking this receptor, an antihistamine like Zyrtec tamps down the classic allergy symptoms in the process, these symptoms, says Dr. Corry. Adults and children aged six and ...