The Central Nervous System Modulatory Activities of N Acetylcysteine: A Synthesis of Two Decades of Evidence As I mention in my book, N acetyl cysteine (NAC) is not found in food sources, but in the body, it converts into cysteine. NAC acts as a precursor to glutathione, a powerful NAC and Glutathione: The Amino Acid the Supplement Industry Is Not Telling You About Green Valley Health and Herbs Serving Elmira for over 30 years