N-Acetylcysteine · supplement
Evidence tier: weak
A foundational antioxidant and mucolytic. Used for respiratory health, liver support, and biofilm driven chronic infections.
NAC supplies cysteine, the rate limiting building block of glutathione, the body's main internal antioxidant. That is the whole basis of the antidote: a paracetamol overdose burns through the liver's glutathione and NAC refills the tank before the toxic metabolite kills hepatocytes. In a person who has not been poisoned there is no depleted tank to refill, which is why the mechanism is real and the consumer claim built on it is not. Separately, NAC breaks the disulphide bonds that make mucus thick, which is its mucolytic action, and it modulates glutamate signalling, which is the leading hypothesis for the psychiatric trials.
NAC is the clearest example in the catalogue of a licensed medicine being sold as a supplement, and the two things must not be confused. As a medicine it is excellent: acetylcysteine is the FDA approved antidote for paracetamol (acetaminophen) overdose and is close to 100 percent hepatoprotective when given within eight hours of ingestion, and it is a licensed mucolytic. None of that transfers to a capsule taken for antioxidant support or detox. There is no evidence that NAC detoxifies a healthy person or that raising glutathione by supplement produces any health outcome a person can feel. Graded by consumer relevant use: airways is the strongest and it is still a disease indication, where the 2019 Cochrane review of mucolytics versus placebo in chronic bronchitis and COPD (38 trials, 10,377 participants) found a small reduction in exacerbations, about one avoided exacerbation every two years, with eight people needing treatment for nine months to keep one person exacerbation free (PMID 31107966). That is a real but modest drug effect in diagnosed lung disease, not a benefit for a well person's chest. Psychiatry is emerging and mixed: the 2024 systematic review and meta analysis of NAC augmentation in obsessive compulsive disorder found six randomised trials in only 195 patients, a modest Y-BOCS improvement that reached significance only in the five to eight week window and not at shorter or longer follow up, and the authors call for large high quality trials (PMC11456833). Trichotillomania and skin picking split the same way: positive in one adult randomised trial, negative in the paediatric trial. A systematic review across major mental disorders found NAC safe but efficacy inconsistent, positive signals in schizophrenia and not in bipolar disorder or major depression (PMID 29457216). The legal status is the other half of the picture: acetylcysteine was approved as a new drug on 14 September 1963, and in 2022 the FDA formally confirmed that NAC is therefore EXCLUDED from the definition of a dietary supplement, choosing only to exercise enforcement discretion rather than to legalise it. Selling it as a supplement rests on an FDA decision not to act, not on a finding that it belongs there.
Supplement products typically supply 600 to 1,800 mg daily. Be clear that the doses that produced the medical results are different: the psychiatric trials generally used 2,000 to 3,000 mg daily for two to three months, and the paracetamol antidote is a hospital protocol (a 21 hour intravenous infusion or a 72 hour oral regimen) that has nothing to do with a capsule.
600 to 1200 mg twice daily, between meals. Cycle off occasionally with long term use.
May reduce effectiveness of nitroglycerin. Smell can be unpleasant, capsules preferred over powder.
Pregnancy: caution
Breastfeeding: caution
Active compounds: N-acetyl-L-cysteine, cysteine, glutathione (the downstream product)
Remedies using NAC (N-Acetylcysteine) · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.