From the Manufacturer:
N-Acetyl Cysteine (NAC) is the pre-acetylized form of the simple amino acid Cysteine. N-Acetyl Cysteine is a powerful antioxidant and a premier antitoxin and immune support substance. Antioxidants neutralize free radicals, which are produced by normal metabolic activity. When free radicals are left unchecked they cause damage to cells and DNA and are considered by scientists to be a major factor in the aging process.
N-Acetyl Cysteine has been shown to provide protection against free radicals as well as a broad range of toxic hazards such as: acrolein (found in barbecue and cigarette smoke and auto exhaust), bromobenzene, paraquat (a toxic herbicide), overdoses of acetaminophen, and the side-effects of cyclophosphamide and adrimycin (anticancer drugs).