Glutathione: the tripeptide, its reduced and oxidized forms, how it is measured, and what its COA covers

What glutathione is: a tripeptide with an unusual bond#

Glutathione is a peptide of three amino acids, glutamate, cysteine and glycine, written γ-Glu-Cys-Gly. The Greek letter is the point of the molecule. In an ordinary peptide, each amino acid is joined to the next through the carboxyl group on its alpha carbon. In glutathione, the glutamate is joined to cysteine through the carboxyl group on its side chain, the gamma carboxyl, not the alpha one ^[1]. That difference means the usual peptidases that cut peptide bonds do not recognize the first bond in glutathione. The chemical name is γ-L-glutamyl-L-cysteinylglycine; the IUPAC name is (2S)-2-amino-5-[[(2R)-1-(carboxymethylamino)-1-oxo-3-sulfanylpropan-2-yl]amino]-5-oxopentanoic acid ^[2].

Cells make glutathione themselves, in two steps that each consume ATP. Glutamate-cysteine ligase (GCL) joins glutamate and cysteine, and glutathione synthetase (GS) adds glycine. GCL is the rate-limiting enzyme, cysteine the limiting substrate, and both enzymes are regulated at several levels, with the transcription factors Nrf2, AP-1 and NF-κB among the controls ^[3]. Shelly Lu's 2013 review in Biochimica et Biophysica Acta describes glutathione as the most abundant non-protein thiol in mammalian tissues and lists its documented roles as antioxidant defense, redox signaling, detoxification of foreign compounds (xenobiotics), cell proliferation, apoptosis, immune function and fibrogenesis ^[3]. Those are roles established in cell and tissue biochemistry; they say nothing about glutathione supplied from outside.

Glutathione formula, molecular weight and CAS number#

The identifiers below refer to reduced glutathione, the free thiol, the form sold as a solid.

Reduced (GSH) and oxidized (GSSG) glutathione, and why the ratio matters#

The cysteine in the middle of the tripeptide carries a thiol (-SH) group, and that thiol is the working part of the molecule ^[1]. When two glutathione molecules are oxidized, their sulfur atoms join in a disulfide bond and the product is glutathione disulfide, GSSG. The enzyme glutathione reductase converts GSSG back to two GSH using NADPH as the source of reducing power ^[1]. Inside an unstressed cell the pool is held mostly in the reduced form; the 2023 review in Metabolites gives a figure of about 90% GSH to 10% GSSG, and intracellular concentrations of roughly 0.5 to 10 millimolar depending on cell type ^[1]. A shift toward GSSG is read as oxidative stress, which is why the GSH:GSSG ratio, not GSH alone, is the usual readout in cell and animal experiments ^[1].

Two enzyme families do most of the work that consumes GSH. Glutathione peroxidases use GSH to reduce hydrogen peroxide and lipid peroxides to water or alcohols, producing GSSG in the process. Glutathione S-transferases attach GSH to electrophilic foreign compounds so that they can be exported from the cell and excreted, which is the detoxification role Lu describes ^[3]. An FDA background description for its 2022 compounding advisory committee says the same: glutathione is synthesized endogenously, the liver is the main source of plasma glutathione, and it is a cofactor for glutathione peroxidases and glutathione S-transferases ^[5].

Oxidation and stability of glutathione as a solid and in solution#

The same thiol that makes glutathione useful makes it unstable in solution. A 2020 preformulation study in Drug Development and Industrial Pharmacy, which the authors describe as the first experimental preformulation dataset for the molecule, measured an aqueous solubility of about 252.7 mg/mL, a log P of −3.1, a melting endotherm near 195 °C with decomposition near 210 °C, and a moisture content below 0.1% for the solid. In forced-degradation experiments the authors identified seven degradation products by LC-MS; the major pathway was oxidation to glutathione disulfide, which followed first-order kinetics ^[6]. In plain terms, the dry solid is a stable crystalline material, and once dissolved GSH converts steadily to GSSG.

Oxidation is not the only route of loss. In a 1980 series of kinetic studies in Chemical and Pharmaceutical Bulletin, Aruga, Awazu and Hanano followed glutathione decomposition in anaerobic aqueous solution at 60 °C, so that oxidation was excluded. They found that cleavage of the γ-glutamyl bond was slowest at pH 5 to 6, fastest at about pH 8.5, and reached a plateau at pH 10 to 12; loss of sulfur (desulfurization) was very slow at neutral pH and sped up markedly as the pH rose. Apparent activation energies were 19 to 21 kcal/mol for both reactions ^[7]. The practical reading is that a mildly acidic, cold, oxygen-free solution is where glutathione lasts longest, and a warm alkaline one is where it is lost fastest. Our guide to storing lyophilized peptides covers the general handling of solids and solutions.

The instability in solution also matters when glutathione is being measured rather than stored. Giustarini and colleagues showed in Nature Protocols that the acid step used to remove protein from a blood or tissue sample oxidizes roughly 5 to 15% of the GSH present to GSSG, which inflates the GSSG reading and distorts the ratio. Their remedy is to trap GSH with N-ethylmaleimide (NEM) before the acid is added, then remove the excess reagent by back-extraction ^[8].

How glutathione is measured: Ellman's reagent, HPLC and LC-MS#

Because GSH and GSSG interconvert, the method determines what a number means. The main approaches:

• Ellman's reagent (DTNB, 5,5′-dithiobis-2-nitrobenzoic acid). Thiols cleave DTNB to release a yellow anion read at 412 nm. The assay measures all DTNB-reactive thiols, so it is not specific to glutathione, and DTNB does not react with GSSG ^[1]. In the enzymatic recycling version, glutathione reductase and NADPH are added so that GSSG is converted to GSH and measured in the same cycle; Giustarini's protocol uses this to quantify GSSG after the GSH has been masked with NEM ^[8].
• HPLC with derivatization. Glutathione has no useful chromophore, so for UV or fluorescence detection it is first tagged with a reagent such as o-phthalaldehyde, monobromobimane or NEM. The Metabolites review calls HPLC the most sensitive of the methods it compares and notes that methods disagree on the same sample, DTNB reading highest and HPLC lowest in one comparison ^[1].
• HPLC-UV for purity of the bulk material. In 2023 FDA scientists presented a validated HPLC-UV method that quantifies reduced glutathione and four related impurities together, validated at 0.1% w/w with impurities quantifiable to 0.03% w/w, and applied it to four commercial glutathione active-ingredient products. The authors note that few validated compendial HPLC methods exist for glutathione ^[9].
• LC-MS and LC-MS/MS. Mass spectrometry identifies GSH and GSSG by mass and fragmentation, with no tag needed. The 2011 trial described below measured erythrocyte GSH, GSSG and their ratio by tandem LC-MS ^[10]. For a bulk solid, LC-MS confirms identity: GSH at a mass consistent with C10H17N3O6S, and any GSSG at roughly twice that mass.

The guide to HPLC and mass spectrometry explains how a chromatogram and a mass spectrum are read in general.

Regulatory status: USP monograph, dietary ingredient, FDA compounding review#

Glutathione has a pharmacopeial standard. The USP-NF Glutathione monograph defines the material as containing not less than 98.0% and not more than 101.0% of C10H17N3O6S on the dried basis ^[4]. That is a specification for the substance, not an approval of any product.

In the United States glutathione is sold as a dietary ingredient, and it has no FDA-approved drug product that we could identify. Two FDA communications from 2019 turn on exactly that distinction. On February 1, 2019, FDA warned compounders not to use glutathione-L-reduced powder distributed by Letco Medical to compound sterile drugs, citing potential endotoxins; FDA was aware of seven patients with adverse events, one of whom was hospitalized, and the powder had gone to about 100 compounders in 30 states ^[11]. A June 7, 2019 compounding alert gave the follow-up: the powder was labeled "Caution: Dietary Supplement", the overseas manufacturer said it marketed the material in the U.S. only for dietary supplements, and that restriction appeared on its invoice but not on the certificate of analysis the distributor received. FDA's testing found excessive bacterial endotoxin in every sample, some at five times the applicable limit ^[12]. A certificate of analysis for a dietary-grade or research-grade powder says nothing about sterility or endotoxin.

Glutathione was also nominated for the list of bulk drug substances that may be used in compounding under section 503A. At the Pharmacy Compounding Advisory Committee meeting of June 8, 2022, FDA proposed that glutathione not be included; the committee voted 8 yes, 5 no and 1 abstention in favor of listing it, with yes votes citing patient access and data showing physical and chemical stability, and no votes citing a lack of evidence of effectiveness for the conditions reviewed ^[13]. The vote is advisory. As of FDA's list updated May 14, 2026, glutathione sits in Category 1, "Bulk Drug Substances Under Evaluation" ^[14]. We did not identify a WADA listing for glutathione.

What the human studies measured#

Glutathione has a small human literature, reported here as what was measured, in whom. None of it is guidance; our article on interpreting peptide research explains the study types.

The two oral trials ask a narrow question, whether glutathione taken by mouth changes glutathione measured in blood cells, and they disagree: the longer trial with more participants saw a rise, the shorter one saw none ^[15][10]. The intravenous literature is thinner; the 2009 pilot in Parkinson's disease found no significant difference from placebo and attributed the inconclusive outcome to its small sample ^[16]. A 2025 narrative review in Cureus describes the wider intravenous literature as small trials with self-reported outcomes, reports adverse events including liver dysfunction and one case of anaphylaxis, and notes a warning from the Philippine FDA against unapproved intravenous use ^[17]; it is cited for the warning and the state of the evidence, not for any effect.

What the research does not cover#

• Whether exogenous glutathione changes glutathione inside tissues other than blood cells in people. The oral trials measured blood compartments and buccal cells ^[15][10].
• Long-term outcomes of any kind. The human studies run from 4 weeks to 6 months.
• Any approved indication. No FDA-approved glutathione drug product was identified, and FDA has proposed against its inclusion on the 503A bulks list ^[13][14].
• Stability of the lyophilized material over years. The preformulation data cover the solid's thermal behavior and forced degradation, not real-time shelf life ^[6].

What the Renuvia glutathione certificate shows#

The certificate currently published for Renuvia's glutathione, lot VB-2609-01-EZ, is a supplier-provided report from KMD Analytical dated October 7, 2026, not a Renuvia-commissioned test. It reports HPLC-DAD purity of 99.51%, identity confirmed, and a measured content of 1,540 mg in a vial labeled 1500 mg, 102.7% of label ^[18]. The report is in the COA library and is labeled there as supplier-provided. Renuvia's own lots are tested by Freedom Diagnostics Testing (HPLC-UV purity, LC-MS identity and measured content); a Renuvia-commissioned glutathione report will be added to the library when it is published, and lots awaiting a report show "pending".

When you read any glutathione certificate, check these points:

1. Which form was tested. The purity figure should be for reduced glutathione (C10H17N3O6S, 307.3 g/mol). A report that does not separate GSH from GSSG is reporting total glutathione.
2. Whether glutathione disulfide is reported as an impurity. Oxidation to GSSG is the main degradation pathway ^[6], so a report that quantifies it is more informative than one that rounds it away.
3. Detector and method. HPLC-DAD and HPLC-UV both read absorbance, and glutathione absorbs weakly, so the report should state the wavelength or derivatization used. Mass spectrometry confirms identity in a way absorbance cannot.
4. Measured content versus purity. Content is the milligrams in the vial; purity is the fraction of what is there that is glutathione. The purity report guide explains why these are confused.
5. Who ran the test. A supplier certificate is the manufacturer's own statement; an independent report names the lab, a report number and a lot code that matches the vial. The guide to verifying that a certificate is genuine covers how to check.
6. What the certificate does not say. Sterility, endotoxin and heavy metals are separate tests. The 2019 FDA alerts show what happens when a certificate for a dietary-grade powder is read as if it covered them ^[12].