Glutathione
GSH, L-glutathione, reduced glutathione
The body's principal intracellular antioxidant, with decent oral trial data, no injectable evidence worth the name, and a skin-lightening market that has outrun both.
Human trials
Sold as a dietary supplement in the United States, which is a legal category rather than a finding of efficacy. Injectable glutathione is not FDA-approved for any indication, and the FDA has warned specifically against injectable products marketed for skin lightening.
What it is
Glutathione is a tripeptide of glutamate, cysteine and glycine, and it is the dominant antioxidant inside human cells. It is not a supplement the body needs to be given so much as a molecule the body continuously makes, uses and recycles, at concentrations far higher inside cells than in blood.
That last point drives most of the confusion around it.
The oral evidence is better than its reputation
For years the standard objection was that oral glutathione is digested into its constituent amino acids and never reaches cells intact, making supplementation pointless.
Randomised trials have complicated that. A six month double-blind placebo-controlled trial in 54 adults at 250 mg and 1000 mg daily found glutathione levels rose at both doses, with increases at six months of roughly 30 to 35% in erythrocytes, plasma and lymphocytes. A separate randomised trial in elderly people with type 2 diabetes reported reduced oxidative damage markers and improved HbA1c over long-term supplementation.
Results across the oral literature remain inconsistent, and bioavailability is genuinely poor. But the flat claim that oral glutathione does nothing is no longer supportable.
The injectable use has none of that
There is no comparable randomised evidence for injected or intravenous glutathione for any of the purposes it is sold for.
The largest market is skin lightening, based on glutathione's inhibition of tyrosinase and its shifting of melanin synthesis toward lighter pigment. Intravenous glutathione infusions for this purpose are widespread in parts of Asia and increasingly elsewhere.
The FDA has warned specifically about injectable glutathione products marketed for skin lightening. Serious adverse events have been reported overseas, including severe cutaneous reactions, and the products themselves are frequently compounded outside any meaningful oversight.
The honest position is that the route with trial evidence is the one nobody markets aggressively, and the route people pay most for is the one with none.
Practical notes
- Plasma glutathione is close to meaningless as a measure. The relevant pool is intracellular. A serum level tells you very little about whether anything useful happened.
- Precursors may be the better route. N-acetylcysteine supplies the rate-limiting cysteine, and randomised work on gamma-glutamylcysteine has raised intracellular glutathione above baseline. Both sidestep the absorption problem rather than fighting it.
- It oxidises fast once in solution. Reduced glutathione is the active form and it does not stay reduced. Discoloured solution is degraded solution.
Side effects and warning signs
Commonly reported
- Oral supplementation is generally well tolerated, with adverse events close to placebo in trials
- Injection-site reactions
- Rare reports of serious reactions with intravenous administration, including anaphylaxis
Stop and get medical help
- Intravenous glutathione for skin lightening, which the FDA has warned about specifically and which has been associated with serious adverse events including Stevens-Johnson syndrome in overseas reports
- Any injectable product from an unregulated source, since sterility rather than the molecule is the main hazard
Sources
From the community
Discussion for this compound concentrates in r/Biohackers and r/Supplements.
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