Glutathione is a tripeptide — γ-L-glutamyl-L-cysteinyl-glycine — and it is not a therapeutic agent that was designed. It is a molecule the body already makes in every cell, at intracellular concentrations of roughly 1 to 10 millimolar, which puts it among the most abundant small molecules in human tissue. It is the principal intracellular thiol antioxidant and the substrate for an entire family of detoxification enzymes.
The unusual bond is worth noting: the glutamate is joined to cysteine through its side-chain gamma-carboxyl group rather than the usual alpha-carboxyl. That linkage makes glutathione resistant to ordinary peptidases and is the reason it survives inside the cell long enough to do its job. It is broken down almost exclusively by gamma-glutamyl transpeptidase on the outer surface of certain cell membranes.
Because glutathione is endogenous and available as a nutritional supplement, it is often treated as though it were free of the questions that apply to other compounds on this site. It is not. The specific question — whether administering glutathione from outside meaningfully changes anything inside a cell — has a long and mostly discouraging literature behind it, and the answer depends heavily on the route.
Glutathione appears here as a Single Peptide because that is what it is chemically. Its evidence base, however, is nutritional and dermatological rather than endocrine, and the controlled human trials that exist studied oral, inhaled, intranasal and topical administration. That distinction matters and is set out in the sections below.
| Weeks | Dosage | Syringe units (U-100) |
|---|---|---|
| Weeks 1–2 | 100 mg | 33.3 units0.33 mL |
| Weeks 3–4 | 150 mg | 50 units0.5 mL |
| Weeks 5–8 | 200 mg | 66.7 units0.67 mL |
FrequencyOnce daily or every other day, subcutaneous.
For review — the controlled human evidence is oral. Richie et al. (2015) established oral amounts of 250 mg and 1,000 mg a day; no dose-ranging trial establishes an injected amount or schedule. The rows in the chart follow a circulated research protocol. The concentration strip above the chart is calculated from the vial and water volume and is correct.
Unverified — no cited trial establishes an injected frequency for glutathione.
The only controlled human dosing for glutathione is oral — a six-month randomised trial of 250 mg and 1,000 mg a day in 54 adults — so the injected amounts charted here are not the amounts that were studied and are flagged for review. Injectable glutathione is widely used for skin lightening, a use that has drawn safety warnings from national regulators rather than trial evidence, and none of the rows above is tied to an outcome any study measured. Glutathione is dosed in hundreds of milligrams rather than fractions of one, so the arithmetic runs the other way from most compounds on this site: Athena lists a single 1,500 mg vial, and made up with 5 mL it comes to 300 mg/mL. At that concentration the 100 mg step is about 33 units, the 150 mg step is exactly one full 50-unit syringe, and the 200 mg step is about 67 units — beyond what that syringe holds, and marked as such.
Measurement note. At this strength and water volume one or more of the amounts above is larger than the 0.5 mL a 50-unit U-100 syringe holds, so it would be drawn with a 100-unit syringe rather than in a single 50-unit fill.
What this evidence establishes. The controlled human dosing evidence for glutathione is oral. Intravenous and intramuscular glutathione have been used clinically, but without dose-ranging trials establishing a standard amount or schedule, and the skin-lightening use often associated with injectable glutathione has been the subject of safety warnings from national regulators. No injectable dose is established here.
Sources: Richie et al., Eur J Nutr 2015 — oral glutathione RCT (n=54)
For educational and laboratory research purposes only. It does not provide medical advice, dosing recommendations, or instructions for human or veterinary use. Syringe units assume a U-100 syringe, on which 1 mL is 100 units and a 50-unit syringe holds 0.5 mL.
Glutathione's biochemistry is well established — it is textbook material, not a hypothesis. What is uncertain is not what glutathione does, but whether supplemented glutathione reaches the compartments where it does it.
The cysteine thiol donates reducing equivalents, cycling between reduced GSH and oxidised GSSG. The GSH:GSSG ratio is the cell's principal measure of oxidative state.
Glutathione S-transferases conjugate glutathione to electrophilic xenobiotics and reactive metabolites, converting them into water-soluble mercapturic acids for excretion.
Made in the cytosol by glutamate-cysteine ligase, the rate-limiting step, then glutathione synthetase. Cysteine availability, not glutathione intake, is normally the constraint.
Glutathione inhibits tyrosinase activity and shifts melanin synthesis from eumelanin toward the lighter pheomelanin. This is the basis of every skin-lightening claim made for it.
Intact glutathione given by mouth is extensively degraded in the gut and liver. Witschi and colleagues found a single 3 g oral dose did not meaningfully raise plasma glutathione in humans.
N-acetylcysteine and similar cysteine donors raise intracellular glutathione by feeding the synthetic pathway. Whether direct glutathione supplementation does the same, and by what route, is what the trials below tried to settle.
Key distinction: almost everything you will read about glutathione's importance is true and refers to endogenous glutathione. Almost nothing about endogenous glutathione's importance is evidence that supplemental glutathione is beneficial. Those are separate claims requiring separate evidence, and only the second one is what a person taking glutathione is relying on.
The literature is fragmented by route. Oral glutathione has the only long-duration randomised evidence, and even there the endpoints are body stores and biomarkers rather than clinical outcomes — nobody has shown that raising measured glutathione stores makes a person healthier. Inhaled glutathione was tested properly in cystic fibrosis and did not work. Intranasal glutathione was tested properly in Parkinson's disease and did not separate from placebo. Injectable glutathione, which is the form most often sold at the highest prices, has the weakest evidence of all: extensive clinical use and essentially no controlled dose-ranging data.
Sample sizes across the whole field are small — the landmark positive trial enrolled 54 people. Trials are short relative to the claims made for the compound. And the skin-lightening application, which drives much of the commercial demand, sits at the intersection of the weakest evidence and the highest reported harm, which is why regulators have addressed it specifically.
Oral glutathione at the doses studied has a benign tolerability record. The safety concerns below attach almost entirely to the injectable route and to the skin-lightening use.
| Condition / Factor | Risk Level | Rationale |
|---|---|---|
| Unapproved intravenous glutathione for skin lightening | WARNED AGAINST | National regulators have issued public advisories against this use, citing serious adverse events reported in association with unapproved high-dose intravenous administration. No regulator has approved glutathione for skin lightening by any route. |
| Non-sterile or compounded injectable preparations | HIGH | Injection of a non-sterile or improperly compounded product carries infection and contamination risk that is independent of the molecule itself. Research-grade material is not manufactured to injectable pharmaceutical standards. |
| Asthma | CAUTION | Bronchoconstriction has been reported with inhaled or nebulised glutathione in susceptible individuals. Relevant to the inhaled route specifically. |
| Sulfur or thiol sensitivity | CAUTION | Glutathione is a thiol compound; hypersensitivity reactions are possible in individuals with known sensitivity to sulfur-containing agents. |
| Concurrent chemotherapy | CONSULT ONCOLOGY | Glutathione participates in the detoxification of electrophilic agents, including some cytotoxic drugs. Any use alongside cancer treatment is a decision for the treating oncology team, not a self-directed one. |
| Pregnancy and lactation | INSUFFICIENT DATA | Supplemental glutathione has not been studied in pregnancy at supraphysiological doses by any route. |
| Expectation of clinical benefit | UNSUPPORTED | The positive trials measured glutathione stores and biomarkers. No trial has shown that supplementation improves a hard clinical outcome in a healthy population. |
United States: oral glutathione is sold as a dietary supplement under DSHEA, which means it is regulated as a food ingredient rather than a drug — no pre-market efficacy review, and structure/function claims only. There is no FDA-approved injectable glutathione product for skin lightening or for general wellness, and FDA has warned about unapproved injectable products marketed for these uses.
Internationally: the Philippine FDA has issued advisories against off-label intravenous glutathione for skin whitening, and other national regulators in Asia have taken similar positions. Some jurisdictions permit hospital use of parenteral glutathione in specific clinical contexts; that is not the same as approval of the cosmetic use.
Sport: glutathione is not on the WADA Prohibited List. Prohibited-list status is about competitive fairness, not safety, and should not be read as an endorsement.
Test your understanding of what glutathione does, why route determines everything, and where the evidence stops.
This profile is for educational and research purposes only. It is not medical advice, and nothing on it is a protocol, a recommendation, or an instruction for use in a person or an animal.
Athena Peptides Education does not prescribe, sell, or recommend any compound. Compounds discussed here are for laboratory research only and are not for human consumption. Always consult a qualified physician before making any decision about your health.