N-Acetylcysteine (NAC)
The cysteine donor that refills glutathione. NAC is hospital standard of care for paracetamol overdose and the most practical way to raise the body's master antioxidant — but the strongest longevity data come from pairing it with glycine, not from taking it alone.
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BiohackingHub Research TeamEditorial Research Team · Last updated: July 31, 2026
Medical Disclaimer: The information on this page is for educational and research purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.
What Is NAC?
N-acetylcysteine is an acetylated form of the amino acid cysteine. That small chemical change makes it stable enough to survive digestion and reach the cells that need it — which matters, because cysteine is the rate-limiting ingredient in glutathione synthesis. Give the body cysteine and it makes more of its master antioxidant. That is the whole premise, and unusually for a supplement, the premise is well established rather than inferred.
NAC has a second life as a hospital drug: it is the standard antidote for paracetamol (acetaminophen) overdose, where it works by restoring the glutathione that the toxic metabolite depletes.
What It Actually Does Well
Paracetamol overdose. This is grade-A territory. A Cochrane review of interventions for paracetamol overdose confirms acetylcysteine as the established treatment — given early enough, it prevents liver failure outright.
Mucus and COPD. The PANTHEON trial randomised over a thousand patients to 600 mg twice daily and found a reduction in exacerbations. This is NAC's oldest and most respectable non-emergency use.
Glutathione repletion — with a caveat. NAC raises glutathione, but the trials that produced the striking results on oxidative stress, mitochondrial function, and physical function in older adults used glycine plus NAC together (GlyNAC). Glutathione is a tripeptide of cysteine, glycine, and glutamate; supplying only cysteine fixes one bottleneck when older adults are often short on both.
Where the Evidence Is Softer
A systematic review of NAC across major psychiatric conditions found signal but heterogeneous, mostly modest effects — enough to justify continued research, not enough to call it a treatment. NAFLD is similar: mechanistic and meta-analytic work points in a favourable direction, but the human outcome data are thin compared with the enthusiasm.
Dosage
| Parameter | Recommendation |
|---|---|
| Low | 600 mg/day |
| Typical | 1200 mg/day (split dose) |
| High | 1800 mg/day |
| Timing | Morning and evening; empty stomach absorbs better, food reduces nausea |
| Best pairing | Glycine 100 mg/kg — the GlyNAC combination |
Safety
NAC has a wide margin and decades of clinical use. The common complaints are gastrointestinal — nausea, bloating, sulphurous burps — and they track with dose. The anaphylactoid reactions described in the literature come from intravenous infusion in overdose care and do not translate to capsules. Asthmatics should be aware that inhaled NAC can provoke bronchospasm; oral use is a different exposure. The one regulatory quirk worth knowing: the US FDA has at times contested NAC's status as a dietary supplement, which is a legal argument, not a safety one.
Related Research
Stacking Interactions
How N-Acetylcysteine (NAC) interacts with other compounds
Protocols using N-Acetylcysteine (NAC)
Evidence-graded stacks that include this compound
Safety Profile — Tier A
Well-tolerated — strong human evidence
Contraindications
- ●Active asthma exacerbation (bronchospasm risk with inhaled forms)
- ●Known cysteine or sulphur-compound hypersensitivity
Side Effects
- ●Nausea, bloating, and sulphurous burps — the most common complaints, usually dose-related
- ●Loose stools at doses above ~1800 mg/day
- ●Anaphylactoid reactions are an intravenous-infusion phenomenon, not an oral-supplement one