Does oral glutathione work?

Richie 2015, a randomised controlled trial, reported increases in body stores. Whether that reflects intact absorption or degradation and resynthesis is less clear.

Gamma-glutamyl transpeptidase on intestinal surfaces degrades glutathione, so its digestive fate is not straightforward.

Why supply cysteine instead?

Cysteine availability usually limits synthesis, so supplying it addresses the actual constraint through the cell's own regulated pathway.

Glutathione

Does Oral Glutathione Reach the Body?

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-233 cited sources

Richie and colleagues published a randomised controlled trial of oral glutathione supplementation on body stores in the European Journal of Nutrition in 2015, reporting increases in measured stores. The question has been contested because glutathione's fate in the digestive tract is not straightforward.

Key facts

Key trial: Richie 2015, Eur J Nutr (PMID 24791752)
Design: Randomised controlled
Endpoint: Body glutathione stores
Why contested: Digestive fate and degradation
Alternative approach: Supplying cysteine instead
Relevant enzyme: Gamma-glutamyl transpeptidase

Why the question arises at all

For most nutrients the digestive tract is a solved problem. For glutathione it is not, because the tripeptide has a specific degrading enzyme — gamma-glutamyl transpeptidase — present on intestinal surfaces. Whether administered glutathione arrives intact, or is broken to its constituent amino acids and reassembled inside cells, is the substance of the disagreement.

What the randomised trial reported

Richie and colleagues ran a randomised controlled trial on body glutathione stores, published in the European Journal of Nutrition in 2015. It is the trial the field cites on this question, and it reported increases in measured stores with supplementation. Randomised and controlled is the right design for the question.

Research material referenced

Glutathione 1500mg — third-party HPLC tested

View — £34.99

The interpretive complication

Increased body stores can arise two ways. Intact glutathione may be absorbed and distributed. Or it may be degraded to glutamate, cysteine and glycine, absorbed as amino acids, and rebuilt — in which case the useful contribution is essentially the cysteine, and the tripeptide is an expensive way to deliver it. A store measurement alone does not distinguish these.

Why cysteine is the alternative

Since cysteine availability usually limits glutathione synthesis, supplying cysteine addresses the actual constraint and works with the cell's regulated pathway rather than around it. This is why cysteine-donor approaches have been pursued as an alternative, and it is a real argument rather than a marketing position.

The parallel with NAD+

The same structural question as the NAD+ category on this site: does supplying the finished molecule work, or does it succeed only by being degraded to precursors the cell can use? For NAD+ the answer is fairly clearly the latter. For glutathione it is genuinely less settled, and the randomised evidence is better.

What is not claimed

That glutathione supplementation produces any health outcome. Raising a measured store is a biomarker result, not a clinical one, and the same gap applies here as everywhere else on this site.

Extended research context

The Glutathione deep dive

Deep dive: the bond that puts a peptide outside peptide biology

Glutamate is one of only two amino acids carrying two carboxyl groups - the backbone alpha-carboxyl every residue has, plus one on its side chain. Standard peptide bonds use the alpha. Glutathione uses the gamma, and that one choice cascades. Ribosomes have exactly one chemistry, in which an incoming residue's amine attacks the growing chain's alpha-carboxyl, and no mechanism whatsoever for recruiting a side chain. So glutathione cannot be a gene product. It is assembled instead by two ATP-dependent ligases, which means the genome encodes the machinery but never the molecule - a peptide present in nearly every cell of nearly every organism, with no coding sequence anywhere. The same geometry that excludes the ribosome also excludes most peptidases, whose active sites are built around the spacing of an alpha bond. Only gamma-glutamyl transpeptidase cleaves it, which puts turnover of a millimolar-concentration metabolite under the control of a single enzyme. Protease resistance by structural mismatch is more complete than anything proline achieves in a conventional peptide.

Deep dive: the one compound here where a purity figure does not tell you what you need

Every storage article on this site says disulfide chemistry is inapplicable, because KPV, Selank, TB-500, DSIP and Semax contain no cysteine at all. Glutathione is the compound those statements were implicitly excluding, and the exception is not marginal - its thiol is simultaneously the source of its function and its principal vulnerability. Two thiols meet, lose two hydrogens, and become GSSG at 612.6 Da. Oxygen drives it, trace metals catalyse it, no enzyme is required, and it proceeds in a vial left standing. The subtle part is that GSSG is not an impurity in the ordinary sense. It is correctly assembled glutathione in a different oxidation state, and a purity assay may well score it as related material rather than contamination. A preparation can be 99% pure and substantially oxidised at once. Where an experiment depends on the reduced form, the certificate does not answer the question - chromatography separating 307.33 from 612.6, or a thiol-specific assay, does.

Deep dive: the same question NAD+ raises, with better evidence and a less obvious answer

Both categories on this site face one structural question: does supplying the finished molecule work, or does it succeed only by being degraded to something the cell can actually use? For NAD+ the answer is fairly clearly the latter - 663 Da with two negative charges cannot cross a membrane, and CD38 degrades it outside the cell. For glutathione it is genuinely open, and the evidence is better. Richie and colleagues published a randomised controlled trial on body stores in the European Journal of Nutrition in 2015, reporting increases. But an increase in stores admits two readings: intact absorption and distribution, or degradation to glutamate, cysteine and glycine followed by resynthesis inside cells - in which case the useful contribution is essentially the cysteine, and the tripeptide is an expensive delivery vehicle for it. Since cysteine availability is what normally limits synthesis, and since gamma-glutamyl transpeptidase sits on intestinal surfaces waiting for exactly this substrate, the second reading is not a sceptical stretch. A store measurement alone cannot distinguish them.

Research applications

▸Cellular redox state measurement via GSH/GSSG ratio
▸Glutathione peroxidase and S-transferase enzyme assays
▸Oxidative stress model systems
▸Gamma-glutamyl transpeptidase activity studies
▸Thiol chemistry and disulfide exchange research
▸Melanin synthesis pathway investigation

Handling checklist

✓Verify against CID 124886, 307.33 Da, C10H17N3O6S
✓Check the oxidised form separately - GSSG is CID 65359 at 612.6 Da
✓Do not treat a purity figure as a statement about redox state
✓Store lyophilised, cold, dry; minimise headspace air
✓Prepare solutions fresh - thiol oxidation proceeds without any enzyme
✓Where the reduced form matters, assay free thiol rather than assuming

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Assuming a high purity figure means the material is reduced

Fix: GSSG is correctly assembled glutathione in a different oxidation state. A purity assay may score it as related material, not contamination.

✗ Treating glutathione like the other peptides on this site

Fix: Its gamma bond makes it protease-resistant and non-ribosomal, and it is the only compound here with a reactive thiol. Most generalisations do not apply.

✗ Reading increased body stores as proof of intact absorption

Fix: Degradation to amino acids followed by intracellular resynthesis produces the same measurement. The trial endpoint cannot distinguish them.

✗ Citing the large biochemistry literature as evidence about supplementation

Fix: What glutathione does inside cells is settled. What supplementing it accomplishes is a separate and contested question.

✗ Repeating systematic review subject matter as a product claim

Fix: Describing what a literature examined and claiming a product does it are different acts. Only the first is permissible.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

Does oral glutathione work?: Richie 2015, a randomised controlled trial, reported increases in body stores. Whether that reflects intact absorption or degradation and resynthesis is less clear.
Why is it contested?: Gamma-glutamyl transpeptidase on intestinal surfaces degrades glutathione, so its digestive fate is not straightforward.
Why supply cysteine instead?: Cysteine availability usually limits synthesis, so supplying it addresses the actual constraint through the cell's own regulated pathway.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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