Cetirizine belongs to the group of anti-allergic drugs, which can be taken usually until 2-3 days after the allergic symptoms have improved, and at most for no more than 7 days. Cetirizine belongs to the second generation of antihistamines and is indicated for allergic dermatitis, allergic rhinitis, allergic conjunctivitis, urticaria and various itching symptoms caused by allergies. Cetirizine has a long half-life. If the patient’s allergic symptoms appear to improve, it can be taken for another 2-3 days, up to a maximum of 7 days, to avoid adverse drug reactions. Although the drug does not easily cross the blood-brain barrier, some patients may still experience anxiety, drowsiness, headache, nausea, vomiting, and palpitations after application. In addition, patients should not take central depressant drugs such as Valium and Gallatin while taking Cetirizine. Avoid driving, drinking alcohol, working at height and fine work, and Cetirizine is not recommended for women who are preparing for pregnancy or breastfeeding.