Cetirizine is an antihistamine medication that helps relieve allergy symptoms such as itchy eyes, runny nose, sneezing, hives, and itching. It works by blocking histamine, a natural substance produced by the body that causes symptoms of allergies. Cetirizine is used to treat hay fever, conjunctivitis, eczema, and other allergic reactions. It is classified as a non-drowsy antihistamine, but some people may still feel sleepy after taking it. Common side effects include headaches, dry mouth, feeling sick, dizziness, and diarrhea. Cetirizine comes in various forms, including capsules, tablets, gels, dissolve tablets, liquid, and chewables. It is generally considered safe and effective for treating allergic rhinitis, urticaria, and allergic conjunctivitis. However, it is important to speak to a doctor before taking cetirizine if you are allergic to it or any other medications, have any medical conditions, or are taking other medicines that make you sleepy.