N-Acetyl-L-Cysteine, or N-A-C, is an acetylated form of the amino acid cysteine. Cysteine is the most important precursor to glutathione (GSH), the most critical antioxidant produced in the body. Promotes respiratory health, helps clear excess mucus. Protects the liver by boosting glutathione levels. Supports detoxification. Gluten-free, non-gmo and vegan.