Glutathione

What it is

Glutathione is a tripeptide of glutamate, cysteine and glycine, and it is not optional. Cells make it continuously, it is the dominant intracellular antioxidant, and it is central to detoxification — paracetamol overdose is treated by replenishing the precursor of it. Nothing about its importance is in dispute.

What is in dispute is everything about taking it as a product. Its first peptide bond is unusual: the link from glutamate to cysteine is a γ-linkage rather than the standard α-peptide bond, which is why it resists ordinary peptidases but is still cleaved by the specific enzyme γ-glutamyltransferase, which sits in abundance in the intestine and liver.

What it does in the body

Glutathione works as a redox couple: reduced glutathione (GSH) donates electrons to neutralise reactive species and becomes oxidised glutathione (GSSG); enzymes reduce it back. The ratio of the two is one of the standard readouts of oxidative stress in a cell. It also conjugates toxins for excretion and regulates aspects of immune cell function.

In skin, the relevant mechanism is different. Glutathione interferes with melanin production — it inhibits tyrosinase and shifts melanin synthesis from darker eumelanin towards lighter pheomelanin. That is the pharmacological basis for the enormous skin-lightening market built around it, particularly in South and Southeast Asia.

What the human evidence shows

The absorption question has a two-part answer, and the parts conflict only if you ignore time.

• Single dose: no. In 1992, seven healthy volunteers were given glutathione at 0.15 mmol/kg — roughly 3 g. Over the following 270 minutes, plasma glutathione, cysteine and glutamate did not rise significantly. The authors concluded systemic availability is negligible in man, attributing it to hydrolysis by intestinal and hepatic γ-glutamyltransferase.
• Four weeks: no. A randomised, double-blind, placebo-controlled trial gave 40 healthy adults 500 mg twice daily for four weeks. Urinary F2-isoprostanes and 8-hydroxy-2′-deoxyguanosine did not differ from placebo, and erythrocyte total, oxidised and ratio measures of glutathione were unchanged.
• Six months: yes. A six-month randomised, double-blinded, placebo-controlled trial in 54 non-smoking adults at 250 or 1,000 mg/day found blood glutathione rose at one, three and six months. At six months in the high-dose group, mean levels rose roughly 30–35% in erythrocytes, plasma and lymphocytes and 260% in buccal cells. Natural killer cell cytotoxicity more than doubled versus placebo at three months. Crucially, levels returned to baseline after a one-month washout.

Skin lightening. A randomised, double-blind, placebo-controlled study gave 60 healthy medical students 500 mg/day orally for four weeks. Melanin index fell consistently at all six measured sites, but reached statistical significance against placebo at only two — the right side of the face and the sun-exposed left forearm. A 12-week three-arm randomised trial of 250 mg/day of reduced and oxidised glutathione found melanin index and ultraviolet spots tended lower than placebo, with significant wrinkle reduction at some sites and a trend toward better elasticity. Both were well tolerated.

A 2018 dermatology review was blunt about the injectable route: the clinical evidence for intravenous glutathione for skin lightening was limited to a single study with a dubious design and apparently flawed analysis. It also noted that parenteral glutathione is approved only for severe liver disorders and prevention of chemotherapy-associated neurotoxicity, and that the absence of statutory control in most countries has allowed unchecked cosmetic use.

Claims and what backs them

Risks and unknowns

This is the entry where documented harm exists, and it comes from the product, not the molecule. The FDA has issued warnings twice:

• 2019. The agency warned compounders not to use glutathione L-reduced powder distributed by one supplier for sterile injectables. The powder was labelled “Caution: Dietary Supplement” and its manufacturer stated it was marketed in the United States only for supplements. Seven outpatients who each received 1,400 mg intravenously on the same day developed nausea, vomiting, lightheadedness, chills, body aches and sneezing within minutes; one had low blood pressure and difficulty breathing and was hospitalised. A separate patient was hospitalised for possible bloodstream infection. FDA testing found bacterial endotoxin at up to five times the appropriate limit.
• August 2026. The FDA reported it was aware of at least 30 patients with adverse events after intravenous glutathione — fever, chills, pain, dizziness, signs of shock and sepsis-like symptoms, with some hospitalisations, consistent with excess endotoxin exposure. The material traced to a single supplement-grade lot. Two Texas pharmacies recalled compounded glutathione for elevated endotoxin, and the supplier told the FDA it had warned US customers not to use the product in injectables.

Endotoxin is a bacterial cell-wall fragment. It is not removed by sterilising filtration and it does not care that the active ingredient is harmless. Supplement-grade material is not manufactured to injectable standards, and no amount of end-product testing substitutes for that.

Oral safety. Oral glutathione was well tolerated across the trials, including at 1,000 mg/day for six months. There is no comparable safety signal for the oral route.

What is not known. Whether raising stores changes any clinical outcome. Whether long-term suppression of melanin has consequences for photoprotection — darker pigment is protective, and deliberately reducing it while increasing sun exposure is not a studied combination.

Where regulators stand

The bottom line

Glutathione is essential biochemistry, a modest and reversible supplement, and a genuinely dangerous injectable when it is made from the wrong grade of powder. Those three sentences are all supported and they point in different directions.

If the goal is raising glutathione stores, months of daily oral intake does it to a limited degree and stops working when you stop. If the goal is lighter skin, the oral trials show partial, site-dependent, reversible effects. If the goal is any of that by injection, the FDA has now documented two clusters of patients harmed by exactly that, and the harm had nothing to do with glutathione itself.

References

1. Witschi A, Reddy S, Stofer B, Lauterburg BH. The systemic availability of oral glutathione. Eur J Clin Pharmacol. 1992;43(6):667–669 PMID 1362956
2. Allen J, Bradley RD. Effects of oral glutathione supplementation on systemic oxidative stress biomarkers in human volunteers. J Altern Complement Med. 2011;17(9):827–833 PMID 21875351
3. Richie JP Jr, Nichenametla S, Neidig W, et al. Randomized controlled trial of oral glutathione supplementation on body stores of glutathione. Eur J Nutr. 2015;54(2):251–263 PMID 24791752
4. Arjinpathana N, Asawanonda P. Glutathione as an oral whitening agent: a randomized, double-blind, placebo-controlled study. J Dermatolog Treat. 2012;23(2):97–102 PMID 20524875
5. Weschawalit S, Thongthip S, Phutrakool P, Asawanonda P. Glutathione and its antiaging and antimelanogenic effects. Clin Cosmet Investig Dermatol. 2017;10:147–153 PMID 28490897
6. Sonthalia S, Jha AK, Lallas A, Jain G, Jakhar D. Glutathione for skin lightening: a regnant myth or evidence-based verity?. Dermatol Pract Concept. 2018;8(1):15–21 PMID 29445569
7. US Food and Drug Administration. FDA highlights concerns with using dietary ingredient glutathione to compound sterile injectables. Compounding alert, 7 June 2019 Source
8. US Food and Drug Administration. FDA reminds compounders not to use dietary supplement grade glutathione in injectables. Compounding alert, 27 August 2026 Source