Dogs can take Zyrtec (cetirizine) safely but only under the guidance of a veterinarian. Zyrtec is often used to relieve allergy symptoms in dogs such as itchy skin, hives, runny noses, and watery eyes. The typical dosage is based on the dog's weight (around 0.5 to 1 mg per pound of body weight) and is usually given once every 24 hours. However, it is critical never to give dogs Zyrtec-D, as it contains pseudoephedrine, a decongestant that is highly toxic to dogs and can cause severe side effects including seizures and death. Dogs with certain medical conditions like kidney or liver disease, pregnant or nursing dogs, and those on other medications may not be able to take Zyrtec safely. Always consult a veterinarian before giving Zyrtec to ensure the proper dosage and to avoid dangerous drug interactions or contraindications.