There is no clear clinical answer to the best cough medicine to reduce phlegm. It is necessary to find the cause of the cough according to the patient’s clinical manifestations and examination results, and to treat the cause and choose the corresponding medication, which is the best for you. Currently commonly used cough suppressants can be classified according to their mechanism: central cough suppressants and peripheral cough suppressants. The former directly inhibits the medullary cough center and can be divided into addictive and non-addictive, with strong cough suppressant effects, mainly codeine phosphate, dextromethorphan hydrobromide, and pentoxifylline citrate; the latter inhibits any of the receptors, afferent nerves, efferent nerves, or effectors in the cough reflex arc and is not addictive, such as noscapine hydrochloride. If the cough is accompanied by difficulty in coughing up sputum, expectorants should be added. If a large amount of sputum accumulates in the body over a long period of time, it is prone to secondary infection and can block the airway, or even cause asphyxia. The former can increase the water content in the sputum and dilute the sputum, including acetylcysteine and deoxyribonuclease; the latter can reduce the viscosity of sputum and make the sputum easy to be expelled, including bromoxynil and aminoglutethimide. All of the above drugs should be used under the guidance of doctors and should not be purchased and taken by oneself.