Paclitaxel requires oral dexamethasone 10mg the night before application, and pemetrexed and docetaxel require oral dexamethasone 5mg in the morning and evening on the day before, the day of, and the day after treatment.The above usage is for scientific reference only, and the specifics of the use of the drug should be strictly in accordance with medical advice. Chemotherapy can cause nausea and vomiting, and may also cause allergic reactions, such as a generalized red rash. The use of dexamethasone during chemotherapy can prevent allergic reactions and reduce vomiting. Oral dexamethasone is often required in the clinic before chemotherapy chemotherapy drugs, mainly including paclitaxel, doxorubicin, pemetrexed and so on. The different ways of using dexamethasone before chemotherapy, intravenous drip or oral, mainly depends on the different chemotherapy drugs used by the doctor to the patient. Clinical application of such drugs before the patient must be instructed to take dexamethasone orally and the specific dose and method, otherwise it may aggravate the patient’s treatment of adverse reactions and aggravate the condition.