How does N-Acetyl cysteine (NAC) work for treating cold symptoms?

N-acetyl cysteine (NAC) may ease cold symptoms by thinning mucus and supporting antioxidant defenses; evidence also suggests it can reduce some influenza-like symptoms.

1. Mucolytic action: NAC breaks down bonds that make mucus thick, loosening it so it can drain from the lungs, nasal passages, and sinuses. This can relieve congestion and sinus pressure, though the increased drainage may mean more nose-blowing. 1
2. Glutathione and oxidative stress: NAC is a precursor to glutathione, an antioxidant involved in reducing reactive oxygen and nitrogen species. These rise during infection, so supporting glutathione may help the body manage infection-related oxidative stress. 2
3. Influenza-like symptoms and immunity: A study using NAC reported fewer influenza symptoms, including runny nose and sore throat, without reducing the number of infections; the discussion also describes improved cell-mediated immunity in earlier research. More randomized studies would help confirm preventive effects. 3