What Does Glutathione Do in the Body? What the Trials Measured

Glutathione is a small molecule of three amino acids, glutamate, cysteine and glycine, that every cell makes for itself, and trial authors describe it as the most abundant antioxidant the body produces. Two placebo-controlled trials of swallowing it found different things: no change in blood glutathione after four weeks at 1,000 mg a day, and stores 30 to 35% higher after six months at the same dose, back to baseline a month after stopping.^{1, 2} Glutathione has no authorised health claim in the UK; what follows is what the trials measured.³ This is the glutathione hub within the Wellgard metabolic and longevity guide.

What is glutathione, and what does it do in the body?

Glutathione is a tripeptide, three amino acids joined in a chain, so a peptide rather than a protein, which cells assemble for themselves from glutamate, cysteine and glycine.⁴ It exists in a reduced form, GSH, and an oxidised form, GSSG, and the ratio between the two is the measure trials use for redox balance. The six-month trial's authors call it "the most abundant endogenous antioxidant" and "a critical regulator of oxidative stress and immune function".¹ Those are descriptions of biochemistry; they attach to no claim.

The "what toxins does it remove" question has a precise answer in pharmacology: liver enzymes attach glutathione to certain drug by-products so they can be excreted, which is why the hospital antidote to paracetamol overdose is acetylcysteine, a cysteine source.⁵ That is a medicine given under supervision, not a property of a capsule, and "detox" is not a claim a UK supplement may make.³

Why is glutathione called the "master antioxidant", and is that a health claim?

"Master antioxidant" is a nickname for the biochemistry above, and it carries no legal weight. The Great Britain nutrition and health claims register, which states that "Only authorised claims in the Great Britain NHC register may be used in Great Britain", has no row for glutathione: no authorised wording and no refused one. Three refused rows mention it in passing, among them the N-acetyl-L-cysteine claim of a "contribution to the normal glutathione formation", judged not substantiated.³ So no UK label or article may attach antioxidant, detox, liver, immune, skin, ageing or energy wording to glutathione or to anything sold to supply it.

Do glutathione levels fall with age?

In the studies that measured it, yes, from the mid-forties. In 169 healthy adults, red-cell glutathione in the 60 to 79 age group was 17% lower than in 20 to 39-year-olds.⁶ In 122 healthy adults, the plasma balance of reduced to oxidised glutathione "was not oxidized prior to 45 years and subsequently was oxidized at a nearly linear rate of 0.7 mV/year".⁷ The reason appears to be supply: eight older adults made glutathione at 45.8% of the pool a day against 83.1% in eight younger people, and after two weeks of extra cysteine and glycine "no differences in these measures were observed between younger subjects and supplemented elderly subjects".⁴ None of this shows that an older person needs a supplement, or what happens to any outcome if levels rise.

What are the signs of low glutathione, and can you test for it?

There is no symptom list, because no study has produced one, and there is no routine NHS test. Glutathione is measured in research laboratories, in red cells, plasma, lymphocytes or cheek cells, which is how every figure on this page was obtained.^{1, 6} What the studies call "low" is a population pattern, lower red-cell levels after 60 and a plasma pool more oxidised each year after 45.^{6, 7} A "glutathione deficiency" is not a diagnosis anyone can make from tiredness, dull skin or slow recovery; a symptom that worries you is a GP question.

Does taking glutathione raise the glutathione in your body?

The two placebo-controlled trials that measured stores over time are the ones to hold together. A four-week trial of 500 mg twice daily in 40 healthy adults found no change in reduced, oxidised or total glutathione and none in two urinary 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, 17 to 29% higher in blood and red cells at 250 mg, a lower oxidised-to-reduced ratio, and levels that "returned to baseline after a 1-month washout period".^{2, 1} 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 by two weeks, with no placebo group and funding from a liposomal-glutathione maker; detail on does liposomal glutathione work.⁸ In 125 people with type 2 diabetes taking 500 mg a day alongside their treatment for six months, blood glutathione rose and a DNA-damage marker fell within three months; an HbA1c change appeared only in a post-hoc subgroup over 55.⁹ No oral trial has measured a clinical outcome in healthy people; daily use, timing and stopping are on how to take glutathione.

Why don't doctors prescribe glutathione?

Because in the UK there is nothing to prescribe. No glutathione medicine holds a UK marketing authorisation; the MHRA's position, published through the Joint Council for Cosmetic Practitioners, is that the imported injection "does not possess a Marketing Authorisation for use in the UK".¹⁰ An unlicensed medicine may be supplied only "when there are no licensed available medicines that can meet the needs of individual patients", and those needs "must be clinical in nature and are determined by the prescriber responsible for their care".¹¹ What is sold in the UK is a food supplement, lawful to sell and allowed no claim.³

Is glutathione good for the liver? What the trials found

Two studies, neither a controlled trial, pointing in different directions. An open-label Japanese pilot gave 300 mg a day for four months to people with non-alcoholic fatty liver disease; in the 29 who completed it the liver enzyme ALT fell significantly, and the authors called for "large-scale clinical trials".¹² A 2026 retrospective analysis of 466 people with cirrhosis taking 500 mg a day for a median of 30 days found the MELD-3 severity score worsened at the population level while 33.5% of patients improved, with "no dose-response relationship", and described the result as "challenging indiscriminate antioxidant use".¹³ So no controlled trial has measured whether glutathione changes the course of a liver condition, "liver detox" is not a claim UK law allows, and anyone with a liver condition asks their specialist first.³

Should you take glutathione, NAD or NMN?

They are different molecules in different systems, and no trial has compared them, so there is no evidence-based ranking in either direction. NAD+ is a coenzyme every cell uses to turn food into energy and to run its repair enzymes, and NMN is the molecule cells convert into NAD+ in one step. Glutathione is a thiol, the cell's own sulphur-based buffer, and its trials measured glutathione stores and oxidative-stress markers.^{1, 2} NMN's own trial record is on what is NMN and is it safe in the UK, and stopping on what happens when you stop taking NMN. No trial has tested the pair, and none of the abstracts read reports an interaction.

What do NAC and GlyNAC have to do with glutathione?

Cysteine usually limits how much glutathione a cell can make, and in older adults glycine can too, which is why the two are studied together as GlyNAC.⁴ The two trials disagree and belong together. A 16-week placebo-controlled trial in 24 older adults, from one US group, found that GlyNAC "improved/corrected" low glutathione, oxidative stress and several other ageing markers.¹⁴ The largest trial, 114 healthy adults with a mean age of 65 taking up to 7.2 g a day for two weeks, found no rise in total glutathione (903.5 mg/L on placebo against 959.6 mg/L, p = 0.278); only a post-hoc subgroup with high oxidative stress and low baseline glutathione rose.¹⁵ NAC on its own is the hospital medicine above, and the register refused its glutathione-formation claim, so a NAC supplement may not make it.^{5, 3} NAC and glutathione are two routes to the same molecule with different trial records; neither is "better". Glycine's own page is does glycine help you sleep, and collagen's glycine is on can I take collagen and glutathione together.

What does vitamin C have to do with glutathione?

Vitamin C has placebo-controlled evidence that it changes blood glutathione, and authorised wording of its own. In 48 adults with low vitamin C, 500 or 1,000 mg a day for 13 weeks raised lymphocyte glutathione by 18%, and it fell back towards baseline over 13 weeks of placebo.¹⁶ A UK label may say that "Vitamin C contributes to the protection of cells from oxidative stress"; that wording belongs to vitamin C and does not transfer to glutathione.³ "Which is better" compares two different things, a vitamin with a daily requirement and a molecule the body makes. They can be taken together; no trial read reports an interaction. Vitamin C's own page is what is vitamin C good for.

Which foods contain glutathione?

Fresh fruit and vegetables and freshly cooked meat. A 1992 survey of the foods on a US food-frequency questionnaire found that "dairy products, cereals, and breads are generally low in GSH; fruits and vegetables have moderate to high amounts of GSH; and freshly prepared meats are relatively high in GSH", with frozen food similar to fresh and other processing causing "extensive loss".¹⁷ No UK food-composition table lists glutathione. Values per food, cooking and depletion are on what foods are high in glutathione.

Is glutathione safe, and who should ask first?

A 2026 review describes gastrointestinal discomfort as the most reported adverse effect of oral glutathione in trials, with "serious toxicities rare"; the four-week trial reported liver, kidney and blood-count tests unchanged, and in the six-month trial the stores that had risen returned to baseline within a month of stopping.^{18, 2, 1} The full cautions are on glutathione side effects. No trial has included pregnant or breastfeeding women or young children, and EFSA's 2026 opinion on S-acetyl glutathione, an acetylated form it assessed as safe at 300 mg a day for adults, excludes pregnant and lactating women and children under 10, so ask a GP or midwife.¹⁹ Inhaled glutathione, a different product, cut lung function (FEV1) by 19% and caused cough or breathlessness in most of eight people with mild asthma, which the authors attributed to sulphite forming from it; anyone with asthma or sulphite sensitivity asks a pharmacist or GP first, although no evidence links capsules to asthma.²⁰ People with liver or kidney disease, or on prescribed treatment for diabetes or Parkinson's, ask the clinician managing it; no trial tested glutathione as a replacement for treatment.

Two uses are a legal and safety matter. No glutathione injection or drip is licensed in the UK, cosmetic use is "not an admissible special need" for an unlicensed medicine, and the harms on record are on are glutathione injections and drips safe in the UK.¹⁰ The skin-lightening trials, what they measured, what they did not, and who to ask are on does glutathione lighten skin.

Frequently asked questions

Does glutathione affect hormones such as oestrogen or cortisol, or reduce belly fat?

No trial has measured oestrogen, testosterone, cortisol, body fat or weight in people taking oral glutathione. There is no sex-specific trial, so "what happens when a woman takes glutathione" has the same answer as for anyone else, and no oral trial in fertility or PCOS exists; the PCOS trials tested NAC, graded on which PCOS supplements have evidence.

Is glutathione good for eczema, itchy skin or hair growth?

No trial has tested oral glutathione in eczema or itch, or measured hair growth or grey hair. Eczema is a condition a GP or pharmacist manages. The nutrients with authorised wording for hair are on collagen for hair and nails. The wrinkle, glow and acne measurements the skin trials did make are on does glutathione make you look younger.

Does glutathione help with hangovers?

In the one blinded trial, a 40-person crossover, people drank 0.78 g of alcohol per kilogram after a yeast extract containing 50 mg of glutathione or a placebo. Serum acetaldehyde was significantly lower with the extract, but there was "no significant difference between the two groups" on the two hangover-symptom scales; three authors were employed by the maker.²¹ That is the whole of the evidence, and UK rules allow no supplement to claim to prevent or cure a hangover.

Do glutathione creams, soaps and serums do anything?

They are cosmetics, not supplements, and the evidence is one maker-run trial: 30 women applied a 2% oxidised-glutathione lotion to one side of the face for ten weeks, the melanin index was lower on that side at ten weeks, and nothing was measured after stopping.²² The larger issue is what is in the jar: UK border checks have destroyed whitening lotions sold under glutathione names that contained 3.1% hydroquinone and two prescription steroids, all prohibited in cosmetics.²³ Check the ingredient list and ask a pharmacist about anything promising to lighten skin.

How do I know if glutathione is working, and why do some people feel good on it?

Not from the outside, because the trials measured blood, not feelings. The four-week trial at 1,000 mg a day found no change at all; in the six-month trial, blood glutathione was above baseline after one month at both doses and back to baseline a month after stopping, so the only measurable "working" is a laboratory reading that lasts as long as the dosing.^{2, 1} A change you notice is yours to weigh; the trials did not measure it. If you feel worse, stomach upset is the effect the trials report; anything beyond that is a pharmacist or GP conversation.¹⁸

Sources

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3. Great Britain nutrition and health claims (NHC) register, 19 May 2026 edition. gov.uk.
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5. Chiew AL, et al. Interventions for paracetamol (acetaminophen) overdose. Cochrane Database of Systematic Reviews, 2018. PubMed 29473717.
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9. Kalamkar S, et al. Randomized clinical trial of long-term glutathione supplementation in elderly type 2 diabetic patients. Antioxidants, 2022. PubMed 35624890.
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11. MHRA. Supply unlicensed medicinal products (specials), updated 29 January 2025. gov.uk.
12. Honda Y, et al. Efficacy of glutathione for the treatment of nonalcoholic fatty liver disease: an open-label, single-arm, multicenter, pilot study. BMC Gastroenterology, 2017. PubMed 28789631.
13. Philips CA, et al. A cluster analysis of 466 patients: glutathione supplementation and cirrhosis phenotypes. Frontiers in Pharmacology, 2026. PubMed 42453576.
14. Kumar P, et al. Supplementing glycine and N-acetylcysteine (GlyNAC) in older adults improves glutathione deficiency, oxidative stress and aging hallmarks. Journals of Gerontology, Series A, 2023. PubMed 35975308.
15. Lizzo G, et al. A randomized controlled clinical trial in healthy older adults of glycine and N-acetylcysteine supplementation on glutathione redox status. Frontiers in Aging, 2022. PubMed 35821844.
16. Lenton KJ, et al. Vitamin C augments lymphocyte glutathione in subjects with ascorbate deficiency. American Journal of Clinical Nutrition, 2003. PubMed 12499341.
17. Jones DP, et al. Glutathione in foods listed in the National Cancer Institute's Health Habits and History Food Frequency Questionnaire. Nutrition and Cancer, 1992. PubMed 1574445.
18. Au S, et al. Efficacy and safety of glutathione supplementation in type 2 diabetes and diabetes complications. Nutrients, 2026. PubMed 42451135.
19. EFSA Panel on Nutrition, Novel Foods and Food Allergens. Safety of S-acetyl glutathione as a novel food pursuant to Regulation (EU) 2015/2283. EFSA Journal, 2026. PubMed 42683004.
20. Marrades RM, et al. Nebulized glutathione induces bronchoconstriction in patients with mild asthma. American Journal of Respiratory and Critical Care Medicine, 1997. PubMed 9279219.
21. Song G, et al. Effects of GSH on alcohol metabolism and hangover improvement in humans: a randomized double-blind placebo-controlled crossover clinical trial. Nutrients, 2024. PubMed 39408229.
22. Watanabe F, et al. Skin-whitening and skin-condition-improving effects of topical oxidized glutathione: a double-blind and placebo-controlled clinical trial in healthy women. Clinical, Cosmetic and Investigational Dermatology, 2014. PubMed 25378941.
23. Office for Product Safety and Standards. Product Safety Report 2301-0119: whitening face and body lotion, 1 February 2023. gov.uk.