Zyrtec (cetirizine) side effects include headaches, dry mouth, and dizziness. Serious side effects are also possible. Learn more about potential side effects, dosing, and when to avoid this over-the-counter antihistamine. Browse ZYRTEC® allergy products for adults and children to learn about proper dosing information and how they may help to relieve your patients’ allergy symptoms. Zyrtec (cetirizine) provides rapid symptom relief for seasonal/perennial allergic rhinitis and hives. It is generally well tolerated; however, mild drowsiness can occur in some patients compared with fexofenadine or loratadine. Cetirizine (Zyrtec) is an antihistamine medication that treats allergy symptoms like itchy eyes, sneezing, a stuffy nose or hives. Whether you need to know ZYRTEC ® dosages for adults or children, check out our dosing charts and FAQs for the ZYRTEC ® family of products, to find all the information you need. Zyrtec is used in adults and children to treat cold or allergy symptoms such as sneezing, itching, watery eyes, or runny nose. Zyrtec is also used to treat itching and swelling caused by chronic urticaria (hives). Zyrtec (cetirizine hydrochloride) is an antihistamine that treats symptoms, such as itching, runny nose, watery eyes, and sneezing from hay fever (allergic rhinitis) and other allergies, such as allergies to molds and dust mites. Cetirizine is a second-generation peripherally selective antihistamine used to treat allergic rhinitis (hay fever), dermatitis, urticaria (hives), and runny nose. [11]. It is taken by mouth. [12]. Effects generally begin within thirty minutes and last for about a day. [12]. What it is: Cetirizine (Zyrtec)—second-generation antihistamine for hay fever and hives. Typical dose: 10 mg once daily; 5 mg may suffice for mild symptoms or kidney impairment. Overview: Cetirizine is an antihistamine that is taken to help treat allergy symptoms, such as a runny nose, itchy or watery eyes, sneezing, or an itchy nose or throat. It may also be used to.