NAC vs glutathione: does oral glutathione work, or should you take NAC instead?

How it works

Glutathione is the main antioxidant inside cells, recycles vitamins C and E, and is the molecule the liver uses to bind and clear many waste products. Cells cannot import much intact glutathione and instead make it, and cysteine is the scarce ingredient. That is the logic for NAC, and the 2014 review in Pharmacology and Therapeutics sets it out: NAC works as an antioxidant only once it has been converted to glutathione inside the cell. The GlyNAC trials in older adults added glycine to NAC, because glycine also runs short with age, and found glutathione levels and several markers of oxidative stress improved over 16 to 24 weeks.

Effective dose

Oral glutathione: 250 mg and 1000 mg a day for six months in the 2015 trial, with the larger rise at 1000 mg. NAC: most supplement trials used 600 to 1800 mg a day; the GlyNAC trials used NAC by body weight, roughly 100 mg per kilogram, alongside the same amount of glycine, which is far above a general supplement dose. There is no UK reference intake for either, because the body makes glutathione and gets cysteine from protein.

Forms compared

NAC is cysteine with an acetyl group attached, which keeps it stable in a capsule and lets it survive the gut. Once absorbed, the acetyl group is removed and the cysteine joins glycine and glutamate inside the cell to make glutathione. Glutathione supplements are the finished molecule, usually as reduced L-glutathione, the active form. Liposomal and sublingual versions claim better absorption; the 2015 trial that showed a rise used ordinary capsules.

Timing

Both are taken with or between meals. NAC has a sulphur smell and taste that some people find easier with food. Glutathione stores changed over months in the trial, so judge either on a three to six month run, not weeks.

Safety profile

NAC at supplement doses can cause nausea, wind or loose stools, and its smell puts some people off. Oral glutathione had no reported side effects in the six month trial. Neither has a UK upper limit. Anyone with asthma should be aware that inhaled NAC can tighten airways; oral doses have not shown that but caution is sensible. Pregnancy and breastfeeding data are limited for both, so ask your GP.

Guideline positions

Randomised controlled trial of oral glutathione supplementation on body stores of glutathione (2015). Effects of oral glutathione on oxidative stress biomarkers in volunteers, four weeks (2011). Existing and potential uses for N-acetylcysteine: the need for conversion to intracellular glutathione (2014). GlyNAC in older adults, randomised trial (2022).

Practical framework

Start with NAC unless it disagrees with you: Nutri Tailor stocks N-acetyl cysteine capsules at 375 mg per capsule, NAC only, made in the UK. If you want the finished molecule, reduced L-glutathione capsules give 200 mg per capsule; the 2015 trial used 250 to 1000 mg a day, so count on more than one capsule and a six month view. Pairing NAC with glycine is the GlyNAC approach and is covered in GlyNAC: glycine and NAC together. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.

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Common misconceptions

That oral glutathione is destroyed in the stomach: the six month trial says otherwise, though the rise was slow. That NAC is glutathione: it is a precursor and only becomes glutathione inside a cell that has enough glycine and glutamate. That a higher glutathione level is always better: the trials measured stores and oxidative markers, not disease outcomes.