CRN: ‘This is not the final word on NAC’ While Amazon moves ahead with removing NAC-containing dietary supplements from its website, the FDA’s Office of Dietary Supplement Programs (ODSP) acknowledges that it is still reviewing the information around the ingredient. NAC (N-acetyl-L-cysteine) is a derivative of the amino acid L-cysteine and is a precursor of the cellular antioxidant glutathione. The ingredient was first approved as an inhaled mucolytic drug in 1963. At present it is used in emergency rooms as a treatment in cases of acetaminophen poisoning to prevent severe liver damage. Despite its early use as a respiratory medication, the ingredient has been widely used for many years in finished dietary supplements, frequently as a standalone product. A search of the Dietary Supplement Label Database from the NIH’s Office of Dietary Supplements yields 1,468 products containing NAC (database accessed May 7, 2021), including some of the biggest brands in the industry.