Phlegmolytic drugs mainly make it easy to cough up by diluting sputum or liquefying mucus. Phlegmolytic drugs can be divided into three categories according to the mode of action: 1. Nauseating and stimulating expectorants, such as ammonium chloride and guaiac glycerol ether belong to nauseating expectorants. After oral administration, they can stimulate the gastric mucosa, cause mild nausea, and reflexively promote increased secretion of respiratory glands, thus diluting phlegm and making it easy to cough up. Stimulating expectorants are volatile substances, such as eucalyptus oil, benzoin tincture, etc. added to boiling water, and their vapor volatilization can stimulate the respiratory mucous membrane to increase secretion and make sputum dilute and easy to cough up; 2. sputum dissolving agents, which mainly decompose the viscous components in sputum, make sputum liquefied, reduce viscosity and easy to cough up, such as acetylcysteine; 3. mucus regulators, which mainly act on the mucus-producing cells of trachea and bronchus to It makes the secretion less viscous and the sputum thinner and easier to cough up, such as bromhexine hydrochloride and carboxymethylstilbestrol. Patients can choose phlegm-suppressing drugs according to their specific conditions and under the guidance of doctors or pharmacists.