N-acetyl-l-cysteine (abbreviated as NAC) is an acetylated derivative of cysteine, which has dual functions of ‌ mucolytic ‌ and ‌ antioxidant ‌, and is widely used in the treatment of respiratory diseases and liver protection. This substance can be converted into glutathione in the body, which helps eliminate free radicals. At the same time, it can break the disulfide bonds of mucin in sputum and reduce the viscosity of sputum. ‌ ‌