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 intracellular B12 processing: Potential role of the glutathione Download Scientific Diagram NAC N Acetyl Cysteine Super Antioxidant Glutathione Precursor Gene The Central Nervous System Modulatory Activities of N Acetylcysteine: A Synthesis of Two Decades of Evidence