N-Acetyl Cysteine is a stable form of the sulfur amino acid L-cysteine, and is a powerful antioxidant. it is a precursor of glutathione, a major antioxidant. Glutathione is activated by the selenium-containing glutathione peroxidase, one of the most important antioxidant enzymes in the body. N-Acetyl Cysteine is better than glutathione supplements, which may break down during digestion and lose potency.