Glutathione is a tripeptide built from three amino acids: glutamate, cysteine, and glycine. Your cells make it on their own, and it's the most abundant thiol antioxidant inside them, with cytosolic concentrations in the low-millimolar range. Chemists know it by the CAS number 70-18-8 and the formula C10H17N3O6S. You'll also see it written as reduced glutathione, L-glutathione, or GSH, the form that does the antioxidant work. When two GSH molecules link up after donating electrons, they form the oxidized disulfide GSSG.
Unlike most compounds this site covers, glutathione isn't an obscure research chemical. It's a core piece of human biochemistry, and the literature on it is deep.
What it does in the body
GSH protects cells from oxidative damage two ways. It reacts directly with free radicals and electrophiles, and it serves as the cofactor for a family of detox enzymes, including glutathione peroxidases, glutathione S-transferases, and glyoxalases. The peroxidase reaction neutralizes peroxides while oxidizing GSH to GSSG; the enzyme glutathione reductase then regenerates GSH using NADPH. That cycle runs continuously. GSH also helps regenerate vitamin E and tunes redox signaling by reversibly modifying protein cysteine residues, a process called S-glutathionylation. See the review in Biochimica et Biophysica Acta for the mechanistic detail.
One well-established clinical role isn't glutathione itself but its precursor. In acetaminophen (paracetamol) overdose, the liver's GSH stores get depleted detoxifying the reactive metabolite NAPQI. The standard antidote, N-acetylcysteine, works largely by replenishing cysteine so the liver can rebuild glutathione. LITFL's toxicology reference lays out that pathway.
The supplement and skin-lightening angle
Most commercial interest in glutathione comes from cosmetic skin lightening, where it's taken orally, applied topically, or injected. The evidence is uneven.
Oral and topical forms have some support. A 2025 systematic review in the International Journal of Dermatology found several randomized trials of oral glutathione (around 250–500 mg/day) reported a measurable drop in melanin index versus placebo, and that combining topical and oral glutathione beat either alone. The catch is durability: how long any effect lasts, and what maintenance would require, isn't settled.
A real complication is absorption. Glutathione taken by mouth is largely broken down in the gut by intestinal gamma-glutamyltransferase, so swallowing it doesn't reliably raise blood GSH the way you'd expect. Some studies report increases with long-term dosing or alternative routes like oral-mucosal delivery, but bioavailability remains a genuine question rather than a solved problem.
Intravenous glutathione is the weakest case and the riskiest. A 2017 review in the Journal of the American Academy of Dermatology concluded there were essentially no studies of IV glutathione for skin lightening or of its safety for chronic use, and flagged a theoretical cancer-risk concern from shifting melanin type. Systematic reviews link IV use to anaphylaxis and hepatotoxicity, made worse by the absence of standardized dosing.
Regulatory and quality status
The US FDA has not approved glutathione for skin whitening. Injectable glutathione is treated as an unapproved drug, and the FDA has specifically warned compounders against using supplement-grade glutathione to make sterile injectables after adverse events tied to contamination. The Philippine FDA and Department of Health have issued public warnings against IV glutathione for cosmetic use. As an oral supplement, glutathione is sold widely but, like other dietary supplements, isn't reviewed for efficacy before sale.
Glutathione is not a banned substance in sport; it's an endogenous molecule, not a WADA-prohibited agent.
For anyone buying research-grade or supplement glutathione, the quality questions are identity and purity, whether the listed form (reduced GSH versus the oxidized GSSG) matches the label, and contamination, which is the central documented hazard with injectables. A current certificate of analysis from the seller, and the third-party rater data peptideone aggregates, are the practical way to check those claims.
This is general information, not medical or dosing advice. Material sold for research is not approved for human consumption. Nothing here endorses any cosmetic or off-label use.