Ranked by how strong the human evidence is — best supported first.
Best supportedLiver markersNot enough evidence· no source yetThen, in order
A tripeptide of glutamate, cysteine and glycine, and the principal intracellular antioxidant. It is made inside cells rather than absorbed intact from the diet in any meaningful quantity.
Glutathione is the antioxidant the body actually uses, and that has made it one of the most heavily marketed and least well-delivered supplements available. Swallowed glutathione is largely hydrolysed in the gut into its constituent amino acids, which is why raising cysteine availability — with N-acetylcysteine, or with whey — is the route that has consistently been shown to raise tissue glutathione. One six-month trial reported increased body stores with oral glutathione, and its interpretation is contested. The most serious issue is not efficacy at all: intravenous glutathione sold for skin lightening has caused severe adverse events, and regulators in several countries have issued explicit warnings against it.
Regulation: Sold as a dietary supplement with no pre-market efficacy review. Several national regulators, including the Philippine FDA, have issued public warnings against intravenous glutathione for skin whitening, citing serious adverse events; the US FDA has warned compounders about unapproved injectable glutathione products.
The amounts, forms and durations published trials of Glutathione actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Oral supplementation and body stores
250–1000 mg
Oral reduced glutathione daily · 6 months
One randomised trial reported increased glutathione in blood and buccal cells at these doses. Earlier pharmacokinetic work found no rise in plasma glutathione after a single large oral dose, and the discrepancy is unresolved.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
Usually taken fasted on the theory that food-derived peptidases further degrade it. No comparison has been published, and the underlying absorption problem is not solved by timing.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Small trials have looked at glutathione in fatty liver disease with inconclusive results. There is not enough human research to support a liver claim.
Not enough evidence. Not enough human research to say anything useful yet.
Oral glutathione is largely broken down in the gut into glutamate, cysteine and glycine, and a single-dose pharmacokinetic study found no rise in plasma glutathione. One longer trial reported increased body stores, and it has not been convincingly replicated, so there is not enough dependable evidence that oral glutathione raises tissue glutathione or changes oxidative stress markers.
What may be going on: Glutathione is synthesised intracellularly, and cysteine availability is the rate-limiting step. Supplying cysteine — through N-acetylcysteine or whey protein — is the route with demonstrated effect.
Not enough evidence. Not enough human research to say anything useful yet.
Randomised controlled trial · The journals of gerontology. Series A, Biological sciences and medical sciences · 2023 · PMID 35975308
Randomised controlled trial · European journal of nutrition · 2015 · PMID 24791752
Systematic review · Journal of cosmetic dermatology · 2019 · PMID 30895708
Deep research mode adds each paper’s own conclusion and stated limitations.
Glutathione is sold for skin lightening on the basis that it shifts melanin synthesis towards the lighter pheomelanin. Trials of oral glutathione for skin tone are small, short and mostly from a small number of centres, and there is not enough evidence to support the use — which is also the use associated with the serious harms.
Not enough evidence. Not enough human research to say anything useful yet.
Systematic review · International journal of dermatology · 2025 · PMID 39444151
Randomised controlled trial · The Journal of dermatological treatment · 2012 · PMID 20524875
Systematic review · Journal of cosmetic dermatology · 2019 · PMID 30895708
Randomised controlled trial · Journal of cosmetic dermatology · 2022 · PMID 33834608
Deep research mode adds each paper’s own conclusion and stated limitations.
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Worth knowing
Injectable glutathione marketed for skin lightening has been linked to Stevens-Johnson syndrome, toxic epidermal necrolysis, kidney injury, thyroid dysfunction and infections from unsterile administration. The Philippine FDA and other regulators have issued explicit public warnings, and the US FDA has acted against unapproved injectable products. No regulator has approved this use anywhere.
Worth knowing
The peptide is hydrolysed by intestinal enzymes, and a single-dose study found no measurable rise in plasma glutathione. Liposomal, sublingual and acetylated forms are marketed as solving this on the basis of small studies with surrogate endpoints.
Interaction
Interacts withChemotherapy agents
Because some cancer treatments work through oxidative mechanisms, high-dose antioxidants during treatment are a question for the treating oncologist rather than a self-directed decision.
Worth knowing
Inhaled glutathione has provoked bronchoconstriction in sulfite-sensitive people with asthma, which is a reason for caution with nebulised preparations in particular.