N-acetylcysteine (NAC) is an acetylated form of the amino acid L-cysteine. It has antioxidant and anti-inflammatory properties and is a mucolytic agent, meaning that it helps break down mucus in the respiratory tract.[1] NAC is converted to L-cysteine after ingestion, which, in turn, is converted into glutathione (GSH), a powerful antioxidant.
L-cysteine can’t be supplemented on its own because free L-cysteine is highly unstable, becoming readily oxidized in solution which can encourage the formation of insoluble precipitates.[2] Similarly, glutathione is rapidly broken down in the gastrointestinal tract and blood, limiting its availability in the body when supplemented directly.[3] In contrast, NAC is more stable and has a much lower toxicity than free L-cysteine,[4][5] making it safer and more effective for increasing cysteine and glutathione levels in the body.