When reading the instructions for use of medicines or consulting some toolkits, words such as caution and contraindication often appear. Mastering the difference between the two is helpful for the rational selection of medicines as well as for ensuring the safe use of medicines by patients. Use with caution refers to the use of drugs to be careful, that is to say, in the use of drugs to pay attention to the observation, if there is an adverse reaction to stop the drug immediately. The term “use with caution” does not mean that the drug should not be used at all, but because it may cause adverse reactions in children, the elderly, pregnant women, lactating women, and patients with cardiac, hepatic, or renal insufficiency. Due to the physiological characteristics or pathology of these people, the body detoxification, detoxification function is low, or the function of some important organs is low, in the use of a certain drug is prone to adverse reactions. Therefore, medication should be used with caution and should be discontinued and consulted with a physician or pharmacist in the event of a problem. Prohibited means that there is no room for choice, belonging to the absolute prohibition of the use of drugs. Once such drugs are taken by mistake, serious adverse reactions or poisoning will occur. Such as peptic ulcer patients are prohibited aspirin, if taken can induce gastrointestinal bleeding; are engaged in mechanical operation, driving a car or ship or aerial work should be prohibited chlorpheniramine maleate, because of the drug’s drowsiness side effects can bring great security risks to the patient. Strictly grasp the “caution” and “prohibited” the difference between the two uses of the drug, and grasp the patient’s medical history before using the drug, in order to ensure the safety of the patient’s use of the drug.