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[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# N-acetylcysteine (NAC)

A cysteine derivative that refills liver glutathione; it is the antidote for acetaminophen poisoning.

Updated 2026-11-01

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## Key facts

- It is deacetylated to cysteine, the amino acid that limits glutathione synthesis.
- Acetaminophen antidote: it refills GSH, supplies sulfate for sulfation and may neutralise some NAPQI directly.
- It protects almost completely when given in the first hours; even late, it improves the course of liver failure.
- It is also a mucolytic: it breaks disulfide bonds in mucus.

**Formula**
C₅H₉NO₃S

**PubChem**
[CID 12035](https://pubchem.ncbi.nlm.nih.gov/compound/12035)

## Structure

- Cysteine with an acetylated amino group; it keeps a free thiol (–SH).

## Clinical notes

- The decision uses the Rumack-Matthew nomogram (acetaminophen level by hours) or any sign of liver injury.
- The intravenous route can cause anaphylactoid reactions (flushing, bronchospasm), usually managed by slowing the infusion.
- Doses and schedules are set by the poison-centre protocol.

## Related conditions

- [Acetaminophen toxicity](https://durgical.com/en/conditions/acetaminophen-toxicity/)

## Related

- [Glutathione (GSH)](https://durgical.com/en/biochemistry/molecules/glutathione/)
- [NAPQI (N-acetyl-p-benzoquinone imine)](https://durgical.com/en/biochemistry/molecules/napqi/)
- [Acetaminophen metabolism and NAPQI](https://durgical.com/en/biochemistry/topics/acetaminophen-metabolism-and-napqi/)

## Test yourself

Think of the answer, then tap the question to see it.

## How does N-acetylcysteine protect the liver in acetaminophen poisoning?

It supplies cysteine to rebuild the glutathione that neutralises NAPQI.

## When is N-acetylcysteine most effective?

In the first hours after ingestion, before glutathione is depleted.

## What typical adverse effect does the intravenous route have?

Anaphylactoid reactions such as flushing, hives or bronchospasm.

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Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [N-Acetyl-L-Cysteine (CID 12035)](https://pubchem.ncbi.nlm.nih.gov/compound/12035) (PubChem, NCBI, 2026); [Acetaminophen overdose: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/002598.htm) (MedlinePlus, US National Library of Medicine, 2026); [Paracetamol ADME](https://reactome.org/PathwayBrowser/#/R-HSA-9753281) (Reactome, 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/molecules/n-acetylcysteine/