NAC vs Glutathione: What Each Is and What the Trials Measured

NAC and glutathione are different molecules. NAC (N-acetylcysteine) is a form of cysteine, the amino acid that usually limits how much glutathione cells make, and in the UK acetylcysteine is also a licensed medicine; glutathione is the finished three-amino-acid molecule. Their trials measured different things, none has compared them on a health outcome, and neither has an authorised UK health claim.^{1, 2, 3} This page is part of the Wellgard glutathione guide.

Evidence at a glance

• Trials: two placebo-controlled GlyNAC trials (24 and 114 older adults), two placebo-controlled swallowed-glutathione trials (40 and 54 adults), one manufacturer-funded crossover of NAC and two glutathione forms (20 adults).
• Largest trial: 114 healthy adults, mean age 65, up to 7.2 g of GlyNAC a day for two weeks.
• Strongest measured outcome: glutathione 30 to 35% higher in red cells, plasma and lymphocytes after six months of 1,000 mg a day of glutathione, back to baseline a month after stopping.
• Not tested: NAC against glutathione on any health outcome; the two taken together.

Sources checked on 13 October 2026.

What is the difference between NAC and glutathione?

NAC is cysteine with an acetyl group attached. In the UK, acetylcysteine is a licensed medicine: by drip in hospital as the antidote to paracetamol overdose, as effervescent tablets for "reduction of sputum viscosity" and as eye drops for tear deficiency.² NAC is also sold as a supplement. Glutathione is made in every cell from glutamate, cysteine and glycine; it is sold as a supplement, and no glutathione medicine is licensed in the UK (see are glutathione injections and drips safe in the UK). The NHS says to get help from NHS 111 if you have taken "more paracetamol than it says on the packet or leaflet".⁴ NAC itself is covered on what NAC is.

How does the body make glutathione from NAC and glycine?

Cells join glutamate, cysteine and glycine; cysteine is usually the one in shortest supply, and in older adults glycine can run low too.^{1, 5} In the best-known study, eight older adults had red-cell glutathione of 1.12 mmol/L against 2.08 in eight younger adults; after two weeks of cysteine (as NAC) with glycine, their glutathione was 94.6% higher and its synthesis rate 78.8% higher, no longer different from the younger group. There was no placebo group.⁵ The assessors refused the wording that NAC contributes to "the normal glutathione formation".³ Food supplies the same building blocks: in a two-week study of 31 adults, 45 g a day of a pressurised whey protein raised lymphocyte glutathione by about 24%, and 15 g did not (more on what foods are high in glutathione).⁶ Glycine has its own page, does glycine help you sleep; collagen's glycine is on can I take collagen and glutathione together.

What did the GlyNAC trials find?

GlyNAC is glycine and NAC taken together, and its two placebo-controlled trials disagree. A 16-week trial in 24 older adults, from one US group, found that GlyNAC, and not placebo, "improved/corrected" low glutathione, oxidative stress, inflammation, physical function and several ageing markers.⁷ In the group's open-label pilot in eight older adults, the benefits "declined after stopping" for 12 weeks.⁸ The largest trial, 114 healthy adults with a mean age of 65 taking 2.4, 4.8 or 7.2 g a day for two weeks, found no rise in total glutathione, its primary endpoint; only a post-hoc subgroup with high oxidative stress and low starting glutathione rose. Most of its authors worked for a company selling glycine and NAC products.⁹

What did the glutathione trials find?

A supplier-funded four-week trial of 500 mg twice a day in 40 healthy adults found no change in red-cell glutathione or in two oxidative-stress markers, while a six-month trial of 250 or 1,000 mg a day in 54 adults found glutathione 30 to 35% higher in red cells, plasma and lymphocytes at the top dose, back to baseline a month after stopping.^{10, 11} A one-month pilot of liposomal glutathione at 500 or 1,000 mg a day in 12 adults found whole-blood glutathione up to 40% higher at two weeks, with no placebo group; it was supplier-funded.¹² The formats are set out on does liposomal glutathione work; none is ranked.

Has anyone compared NAC and glutathione?

Once, on blood markers. A crossover in 20 adults with metabolic syndrome gave each person three weeks each of a sublingual glutathione tablet, swallowed glutathione capsules (450 mg a day of each) and NAC (200 mg a day), according to the full text.¹ Plasma glutathione and the reduced-to-oxidised ratio were higher in the sublingual period than in the swallowed one. The tablet's maker sponsored the study and employed two authors, the doses differed, and only blood markers were measured.¹ No trial has compared NAC and swallowed glutathione on any health outcome: they are two routes to the same molecule with different trial records, so neither is "better".

Can you take NAC and glutathione together?

No trial has tested the two taken together. A 1991 review of NAC lists glutathione, paracetamol and anticancer medicines as clinically significant interactions.¹³ If you take any medicine, ask a pharmacist first, particularly about a nitrate for angina: in a 1992 study of 11 healthy volunteers, NAC made nitrate headaches worse.¹⁴ Side effects are on NAC side effects and glutathione side effects.

Is NAC the same as NAD or NMN?

No. NAD (nicotinamide adenine dinucleotide) is a coenzyme cells use to release energy from food, and NMN (nicotinamide mononucleotide) is converted into NAD in the body; neither contains cysteine or is a glutathione building block. NMN's trials and UK position are on what is NMN and is it safe in the UK.

What we don't know

• No trial has compared NAC with glutathione, or GlyNAC with either, on a health outcome.¹
• No trial has tested NAC and glutathione taken together.
• Effects a person would notice rest on small trials: walking speed and strength in the GlyNAC trial and pilot, and exercise tests in a 36-person NAC crossover where only people starting low improved.^{7, 8, 15}
• The positive GlyNAC results come from one research group; the larger trial from another team did not reproduce them overall.⁹

Frequently asked questions

Is NAC a glutathione supplement?

No. NAC is a source of cysteine, one of glutathione's three building blocks, not glutathione itself. The assessors refused the claim that it contributes to "the normal glutathione formation", and NAC has no authorised health claim in Great Britain.³

Does NAC actually increase glutathione?

In a small study it did; the largest trial did not show it overall. Eight older adults taking NAC with glycine for two weeks had 94.6% higher red-cell glutathione, with no placebo group; in 114 healthy older adults, GlyNAC did not raise total glutathione against placebo, except in a post-hoc subgroup.^{5, 9}

Is GlyNAC better than glutathione?

No trial has compared them. GlyNAC has a positive 24-person trial and a 114-person trial with no overall rise; swallowed glutathione has a four-week trial with no change and a six-month trial in which stores rose 30 to 35%.^{7, 9, 10, 11}

Which is better for the liver, NAC or glutathione?

Neither has been shown better. NAC's liver use is a hospital treatment: acetylcysteine by drip for paracetamol overdose.² Glutathione's small liver studies are in the glutathione guide; a liver question is one for your GP.

Should I take NAC or glutathione every day?

No trial answers that for a particular person. Trials gave glutathione daily for up to six months and GlyNAC for up to 24 weeks; the six-month rise fell back within a month of stopping.^{8, 11} Daily use and timing are on how to take glutathione; with any medicine, ask a pharmacist first, especially about NAC.

Sources

1. Schmitt B et al. Redox Biology 2015. Randomised crossover, 20 adults, three 3-week periods; manufacturer-funded, two authors employed by the manufacturer. PubMed 26262996
2. NICE British National Formulary. Acetylcysteine monograph, accessed 13 October 2026. bnf.nice.org.uk/drugs/acetylcysteine
3. Great Britain nutrition and health claims register, 19 May 2026 edition. Statutory register. gov.uk
4. NHS. Paracetamol for adults. Page last reviewed 24 March 2026. nhs.uk
5. Sekhar RV et al. American Journal of Clinical Nutrition 2011. Before-and-after study, 8 older and 8 younger adults, 2 weeks, no placebo; charity and government funded. PubMed 21795440
6. Zavorsky GS et al. International Journal of Food Sciences and Nutrition 2007. Randomised dose comparison, 36 adults (31 finished), 2 weeks. PubMed 17710587
7. Kumar P et al. Journals of Gerontology, Series A 2023. Randomised placebo-controlled trial, 24 older adults, 16 weeks; government and charity funded, no conflicts declared. PubMed 35975308
8. Kumar P et al. Clinical and Translational Medicine 2021. Open-label pilot, 8 older adults, 24 weeks plus 12 off; charity-funded, no conflicts declared. PubMed 33783984
9. Lizzo G et al. Frontiers in Aging 2022. Randomised placebo-controlled trial, 114 adults, 2 weeks; most authors employed by a company selling glycine and NAC products. PubMed 35821844
10. Allen J, Bradley RD. Journal of Alternative and Complementary Medicine 2011. Randomised placebo-controlled trial, 40 adults, 4 weeks; supplier-funded. PubMed 21875351
11. Richie JP Jr et al. European Journal of Nutrition 2015. Randomised placebo-controlled trial, 54 adults, 6 months; funding not checked. PubMed 24791752
12. Sinha R et al. European Journal of Clinical Nutrition 2018. Uncontrolled pilot, 12 adults, 4 weeks; supplier-funded. PubMed 28853742
13. Holdiness MR. Clinical Pharmacokinetics 1991. Narrative review. PubMed 2029805
14. Iversen HK. Clinical Pharmacology and Therapeutics 1992. Randomised placebo-controlled crossover, 11 healthy adults. PubMed 1505148
15. Paschalis V et al. Free Radical Biology and Medicine 2018. Placebo-controlled crossover trial, 36 adults, 30 days; funding not checked. PubMed 29233792

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