N-acetylcysteine / NAC

Also known as NAC, n acetyl cysteine, acetylcysteine.

Last reviewed October 9, 2026 · Jump to references

What is N-acetylcysteine / NAC?

In plain words

NAC is a modified form of cysteine, one of the building blocks of protein. The body can turn it into cysteine to make glutathione, a substance that helps protect cells from damage; NAC also helps loosen thick mucus. Researchers study it for several lung and mental health conditions, alongside its established medical roles in mucus thinning and treating acetaminophen poisoning. Evidence for broader supplement benefits is mixed, and NAC can cause nausea and other side effects.

Technical definition

N-acetylcysteine (NAC; acetylcysteine) is an N-acetylated derivative of the sulfur-containing amino acid L-cysteine, rather than a peptide. It supplies cysteine for synthesis of glutathione, an intracellular antioxidant, and its free thiol group reduces disulfide bonds in mucus proteins, lowering mucus viscosity rather than acting through a specific receptor. Acetylcysteine is an FDA-approved drug for specific indications, including acetaminophen poisoning and mucus thinning; NAC is also marketed in supplement products, whose regulatory treatment varies by jurisdiction.

Educational information only. This page does not provide medical advice or determine whether a supplement is appropriate for you. Review supplements with a qualified healthcare professional, especially if you take medication, are pregnant, have surgery scheduled, or have a chronic medical condition.

Evidence by use

Each use is rated on its own. There is no single overall effectiveness score.