Glutathione: roles, absorption and supplemental forms

Glutathione is often described as the body's “master antioxidant”. All our cells make it, and it helps neutralise oxidants and eliminate many substances. It is also sold as capsules, liposomes or injections, with promises sometimes far removed from evidence. Here is what is known about its role, absorption when swallowed, precursors, studied doses and safety.

What is glutathione?

Glutathione is a tripeptide, a short chain of three amino acids: glutamate, cysteine and glycine. It is the most abundant small sulphur-containing compound in our cells, which make it themselves from these three building blocks. Cysteine provides a thiol group, a reactive sulphur atom underlying its properties.

It exists in two forms. Reduced glutathione, GSH, is the active form. When neutralising an oxidant, two GSH molecules join to form oxidised glutathione (GSSG), which the cell then recycles using NADPH, a close cousin of NAD+. As with the NAD+ and NADH pair, this movement between two forms is central to the cell's chemical balance.

What does glutathione do in the body?

It has three main functions:

• Antioxidant defence: it directly neutralises certain oxidants and partners with enzymes such as glutathione peroxidase, which destroy hydrogen peroxide.
• Removal of foreign substances: it binds to medicines or pollutants transformed by the liver to facilitate their elimination.
• Redox balance: it maintains many proteins in their active state.

Its level can fall. It is low in plasma in people with HIV infection, alcoholism or cirrhosis. In eight older people, a study measured red blood cell glutathione almost twice as low as in eight young adults, because of slower synthesis.

Is swallowed glutathione absorbed?

This is the major question, and studies conflict. In the intestine and liver, an enzyme, gamma-glutamyltransferase, breaks glutathione into its amino acids. In 1992, a single dose of around 3 g in seven volunteers did not increase blood glutathione. In 2011, a controlled trial in 40 adults observed no change in red blood cell glutathione or oxidation markers after four weeks at 1,000mg daily.

A longer trial qualified this picture. In 54 non-smoking adults, 250 or 1,000mg daily for six months increased blood glutathione from the first month. At the high dose, the rise reached 30 to 35% in red blood cells, plasma and lymphocytes, before returning to baseline one month after stopping. This study was supported by the tested ingredient's manufacturer. Swallowed glutathione may therefore be partly used, but the effect takes time and regularity. This absorption problem is not unique to glutathione: it also concerns resveratrol and its low bioavailability.

Liposomal, sublingual and S-acetyl: “improved” forms

The most common form remains reduced glutathione in capsules, such as Hexagon® reduced glutathione 300mg (300mg per capsule). Other forms seek better protection of glutathione. In a pilot study of 12 adults without placebo, 500 to 1,000mg daily of liposomal glutathione, enclosed in tiny lipid bubbles, increased whole-blood glutathione by up to 40% in two weeks. In a three-week crossover trial in 20 people with metabolic syndrome, a sublingual form raised plasma glutathione more than encapsulated glutathione or NAC. These findings remain preliminary. For differences between capsules, softgels and other forms, see our dedicated article.

Finally, in 2026, the European Food Safety Authority (EFSA) considered an acetylated form, S-acetyl glutathione, safe at up to 300mg daily in adults. Its opinion notably draws on available human data for oral glutathione.

NAC and glycine: using precursors

Since cells make their own glutathione, another strategy is to supply missing building blocks. NAC, a cysteine source, is the most widely used. In eight older people, two weeks of cysteine and glycine supplementation almost doubled red blood cell glutathione (+95%) and reduced oxidation markers. A sixteen-week controlled trial in 24 older people using glycine and NAC confirmed correction of deficiency, with effects on several ageing markers. These trials are small and from the same team: they need replication.

Can you increase glutathione through diet?

Glutathione occurs in foods. An analysis of common US foods prepared as consumed showed moderate to high amounts in fresh fruit and vegetables, and high amounts in fresh meats. Dairy, cereals and bread are low in it. Freezing preserves it, but other processing and storage methods cause substantial losses.

As dietary glutathione is also broken down in the intestine, it does not strongly determine blood levels. Diet mainly matters through the building blocks supplied: cysteine and methionine from protein, and glycine.

Glutathione and lighter skin: what do studies say?

In the laboratory, glutathione slows melanin production, explaining its popularity as a lightening agent. In humans, evidence is thin. In a four-week Thai trial in 60 medical students, 500mg daily reduced the melanin index more than placebo at only two of six measured sites. The duration of this effect is unknown. A 2016 review concluded that intravenous injections, despite widespread use, have no evidence of efficacy; adverse effects led the Philippine health agency to warn against this use.

What dose of glutathione?

Multi-week trials used 250 to 1,000mg daily, in one or two doses, for four weeks to six months.

Adverse effects and precautions

Oral glutathione was well tolerated in available trials, and EFSA considers human data reassuring in adults. Some precautions are nevertheless necessary:

• Asthma: inhaled as an aerosol, glutathione caused bronchoconstriction in eight asthma patients. This is not the supplement form, but the risk should be known.
• Injections: cosmetic infusions have no evidence of efficacy and carry adverse effects.
• Pregnancy and breastfeeding: data are lacking. EFSA excluded these situations from its favourable S-acetyl glutathione opinion.

No health claim is authorised for glutathione in the European Union.

Frequently asked questions

Glutathione or NAC: which should you choose?

Both target the same goal through different routes. NAC provides the cysteine cells need to make their own glutathione; oral glutathione attempts to supply the whole molecule. No trial has compared their long-term health effects.

When should glutathione be taken: fasting, morning or evening?

No study has compared intake times. Trials used one or two daily doses. Regularity appears more important: in positive trials, the rise occurred after one to four weeks of daily use.

Can glutathione be combined with vitamin C?

There is no reason to rule it out, and both molecules work in a network within cells. No trial has, however, shown a benefit of the combination. Under regulations, vitamin C has an authorised claim: it “contributes to the protection of cells from oxidative stress”, as do vitamin E, selenium and zinc.

Is glutathione good for the liver?

Glutathione plays a key role in the liver's elimination of medicines and pollutants. However, no trial has shown that a glutathione supplement improves a healthy liver's function. Plants traditionally associated with the liver are presented in our article on milk thistle.

Does glutathione help with weight loss?

There is no basis to claim this. The cited trials measured blood glutathione, oxidation markers or skin colour, not changes in weight.

How can you tell if you are low in glutathione?

This is not a routine examination. Glutathione is mainly measured in research, in blood or red blood cells, using specialised techniques. Symptoms such as fatigue cannot establish deficiency.

Conclusion

Glutathione is central to cellular defence, but a glutathione supplement is not an obvious choice. When swallowed, much is broken down: short trials show nothing, while a six-month trial shows a moderate, reversible rise in stores. Liposomal or sublingual forms and precursors such as NAC and glycine show encouraging results, but from small studies. Skin lightening rests on too little evidence to justify promises, still less injections. If considering it, discuss it with a healthcare professional, especially in asthma, pregnancy or medication use.

Sources

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Food supplements do not replace a varied, balanced diet or a healthy lifestyle. Ask a healthcare professional for advice if you are taking medication, pregnant or breastfeeding.