N-acetylcysteine (NAC) is a derivative of the naturally occurring amino acid, cysteine. NAC has an extensive history of use as a mucolytic (breaks down mucous) in the treatment of acute and chronic lung conditions such as emphysema, bronchitis, chronic asthma, and cystic fibrosis. It directly splits the sulfur linkages of mucoproteins thereby reducing viscosity of bronchial and lung secretions. As a result it improves bronchial and lung function, reduces cough, and improves oxygen saturation in the blood.

In detailed analysis of 39 human trials it has been concluded that oral NAC reduces the risk of exacerbations (severe worsening) and improves symptoms in patients with chronic bronchitis compared with a placebo.

In addition to its benefits to respiratory health, NAC is serves as a nutritional precursor for the synthesis of glutathione, which is a powerful antioxidant. Glutathione also detoxifies chemicals into less harmful compounds. N-Acetyl Cysteine has also been shown to be effective in treating liver failure and detoxifying heavy metals from the body.