Hi, Zyrtec contains cetirizine hydrochloride which belongs to the group of medications known as antihistamines is used to help provide 24 hour relief due to hay fever or other upper respiratory allergies. When the sniffing season hits, Zyrtec can be taken as an effective allergic medication to help you muddle no more. Zyrtec relieves your worst indoor and outdoor allergy symptoms. Common indoor allergens include dust mites, pet dander and mold. Outdoor allergens, depending on the season and your location, include grass pollen, tree pollen and molds. Such allergens would seem like invaders in the body and trigger allergy symptoms as the body reacts to these. Zyrtec can be used for relief of the some common allergy symptoms like runny nose, sneezing, itchy eyes, itching of the nose or throat etc. Antihistamines like Zyrtec basically works by drying you up, so anything involving fluid in your body will decrease- including urine. Thus, they can cause urine to become dark and appear brown. Plenty of fluids intake may help to subside this side effect. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician