Glutathione is three amino acids — glutamate, cysteine and glycine — but it is not a peptide in the usual sense. The bond between glutamate and cysteine runs through glutamate's side chain rather than its backbone, which is why the enzymes that chop up ordinary peptides leave it alone, and why it is built by two dedicated enzymes rather than by the ribosome that makes every other peptide in the body. It is the most abundant small thiol in cells, present at concentrations of one to ten millimolar, and its job is to hand electrons to reactive molecules before they damage lipids, proteins or DNA, and to help enzymes detoxify drugs and metabolites. The cysteine is the working part; the other two residues keep it inside the cell and out of reach of peptidases.

GlutathioneWhat the studies show

Q: What kind of evidence exists for glutathione?

Small human studies. One careful 16-person study of the precursors in older adults, three small trials of oral glutathione that disagree about absorption, and decades of settled biochemistry; nothing on long-term outcomes.

The most abundant small antioxidant in human cells: three amino acids joined by a bond that ordinary peptidases cannot cut.

5 min read · Small human studies · Updated November 2026

In short

Name: glutathione (sold by Progression Labs as Glutathione)
Evidence: Small human studies
Bottom line: One careful 16-person study of the precursors in older adults, three small trials of oral glutathione that disagree about absorption, and decades of settled biochemistry; nothing on long-term outcomes.

Before you read this

This guide explains what published studies found. That is all it is.

It is not medical advice and it is not instructions for using anything. Where a dose appears, we are reporting what a named study gave the people or animals in it — a fact about the study, not an instruction to you.

The compounds here are not approved by the FDA for use in people and are sold for laboratory research only. A study tells you what happened to the subjects in it; it does not tell you what would happen to you. Talk to a doctor first.

What it is

Glutathione is three amino acids — glutamate, cysteine and glycine — but it is not a peptide in the usual sense. The bond between glutamate and cysteine runs through glutamate's side chain rather than its backbone, which is why the enzymes that chop up ordinary peptides leave it alone, and why it is built by two dedicated enzymes rather than by the ribosome that makes every other peptide in the body ¹. It is the most abundant small thiol in cells, present at concentrations of one to ten millimolar, and its job is to hand electrons to reactive molecules before they damage lipids, proteins or DNA, and to help enzymes detoxify drugs and metabolites ¹. The cysteine is the working part; the other two residues keep it inside the cell and out of reach of peptidases.

The studies below call this molecule glutathione. Progression Labs sells it as Glutathione; the guide uses the store's name and the papers use theirs.

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Why it falls with age

The 2011 study that most of the longevity interest rests on is small and careful. Rajagopal Sekhar's group at Baylor compared eight healthy adults aged 60 to 75 with eight aged 20 to 30, using labelled amino acids to measure how fast red blood cells made glutathione. The older adults had about half the red-cell glutathione of the young, and they made it more slowly; the shortfall traced to low levels of its two limiting ingredients, cysteine and glycine ². Giving the older group those two amino acids — cysteine as N-acetylcysteine, plus glycine — for 14 days brought synthesis rates and glutathione concentrations back to the young adults' levels, and markers of oxidative damage in plasma fell ².

Eight people is eight people, and the study measured blood chemistry, not how anyone felt or aged. But it is the clearest demonstration that the age-related fall is a supply problem rather than a fixed feature of older cells.

The absorption question

Whether glutathione swallowed as a supplement reaches the blood intact was the subject of a 1992 study that is still quoted: seven volunteers were given a single 3-gram dose, and their plasma glutathione did not rise over the following hours, which the authors attributed to a gut enzyme, gamma-glutamyl transpeptidase, breaking it down ³. A 2011 trial of 500 mg twice a day for four weeks in 40 adults also found no change in blood glutathione or in markers of oxidative stress ⁴.

Against that, a 2015 randomised trial gave 54 adults 250 or 1,000 mg a day for six months and reported that glutathione in red cells, plasma and lymphocytes was about 30 to 35% higher on the larger amount by month six, rising gradually rather than after each dose ⁵. The honest summary is that single doses do not show up in plasma, and that months of daily intake raised stores slowly, in one trial, by a modest amount. Glutathione given by vein skips the gut, but there is no large controlled trial of it for any ageing-related purpose.

What it does in cells

Glutathione's chemistry is settled; its effect as a supplement is not. Inside a cell it is the main buffer that keeps the environment reducing: the ratio of reduced glutathione to its oxidised form, GSH to GSSG, is one of the standard laboratory measures of oxidative stress, and it drops in ageing tissue, in liver disease and in the lungs of smokers ¹. The enzymes that depend on it — glutathione peroxidases and glutathione S-transferases — are what the body uses to neutralise hydrogen peroxide and to tag foreign compounds for excretion ¹. N-acetylcysteine, the cysteine precursor in the Baylor study, is itself an approved drug for acetaminophen overdose because it restocks liver glutathione quickly ⁶. That is the best-established clinical use of glutathione chemistry, and it is a use of the precursor, not the tripeptide.

Status, and what is not known

In the United States glutathione is sold as a dietary supplement; it is not an FDA-approved drug for any condition. The trials above measured blood levels and chemical markers over weeks to months in a few dozen people. No trial has followed glutathione supplementation long enough, or in enough people, to say anything about how they age, and the one study that restored levels in older adults did it with the precursors rather than with glutathione itself ².

What these studies are, and aren't

Small human studies. One careful 16-person study of the precursors in older adults, three small trials of oral glutathione that disagree about absorption, and decades of settled biochemistry; nothing on long-term outcomes.