Glutathione Dosage and Side Effects: What Trials Used

Glutathione is unusual among the compounds on this site: real, specific, randomized human doses genuinely exist for it. Adults have taken 500 mg by mouth for four weeks, 1,000 mg a day for six months, 200 mg intranasally three times daily for three months, and 646 mg twice daily by nebulizer for half a year, all inside published, controlled trials. What makes the dosing question hard is not an absence of numbers — it is that almost none of those numbers describe the injectable route this site's 19-seller glutathione board mostly ships, and the most recent systematic review to look at that route reaches a conclusion no dosing chart can be built on top of.

Our glutathione evidence review sorts the compound by product and asks whether it works. This article asks the narrower question: what amount was actually put into a person, by which route, for how long, and what happened.

The IV route: one randomized dose in the entire literature, and a review that says not to use it

Exactly one randomized, placebo-controlled human trial has established an IV glutathione dose, and it was not a skin study. Twenty-one Parkinson's disease patients were "randomly assigned to receive intravenous glutathione 1,400 mg or placebo administered three times a week for 4 weeks"¹. On safety, the trial's own text is clean and worth quoting exactly: "Glutathione was well tolerated and there were no withdrawals because of adverse events in either group. Reported adverse events were similar in the two groups." On efficacy, it was equally plain: "There were no significant differences in changes in Unified Parkinson's Disease Rating Scale (UPDRS) scores," with the authors noting only "the possibility of a mild symptomatic effect" needing a larger study.

That is the whole randomized IV dosing record. A 2025 systematic review of glutathione as a skin-lightening agent — the indication IV glutathione is overwhelmingly sold for — confirms the scarcity from the other direction: "There was only one placebo-controlled study on intravenous (IV) glutathione," and its reported result was not significant (37.5% versus 18.7%, p 0.054)². That review's own conclusion about the route is the sentence that makes a dosing chart impossible to write honestly: "IV glutathione is contraindicated due to lack of efficacy and side effects."

A separate 2016 review — a review, not a trial, and reported here as one — supplies the regulatory context behind that judgment: "Although the use of intravenous glutathione injections is popular, there is no evidence to prove its efficacy. In fact, the adverse effects caused by intravenous glutathione have led the Food and Drug Administration of Philippines to issue a public warning condemning its use for off-label indications such as skin lightening"³. Neither of those reviews reports a specific IV dose that has been validated for anything, because none has been.

The oral route: three doses, tested repeatedly, with a real ceiling on what they do

Oral glutathione is where the numbers are firmest, and they are modest.

• •250 or 1,000 mg/day, six months. A randomized, double-blinded, placebo-controlled trial in 54 non-smoking adults tested both doses against placebo for half a year and measured body glutathione stores rather than a clinical outcome. At six months, "mean GSH levels increased 30-35 % in erythrocytes, plasma and lymphocytes and 260 % in buccal cells in the high-dose group," with the low-dose group up 17% in blood and 29% in erythrocytes⁴. The dosing-relevant detail: "In most cases, the increases were dose and time dependent, and levels returned to baseline after a 1-month washout period." Sustained daily dosing is what produced the effect; stopping erased it within a month.
• •500 mg/day in two divided doses, four weeks. A randomized, double-blind, placebo-controlled study in 60 healthy adults measured skin melanin index at six sites. Melanin "decreased consistently at all six sites in subjects who received glutathione," but "the reductions were statistically significantly greater than those receiving placebo at two sites" only — the right side of the face and the sun-exposed left forearm⁵. Both glutathione and placebo were, in the study's own words, "very well tolerated." The authors' own caveat is worth carrying: "long-term safety has not been established and warrants more extensive clinical trials."
• •The dose set the field has actually studied. The 2025 systematic review names it precisely: "Five randomized controlled trials and a single open-arm clinical study on oral glutathione at doses of 250 mg once a day, 250 mg twice a day, and 500 mg once a day showed a significant reduction in the melanin index compared to placebo"². That is the full range of oral doses with randomized support behind them — not a milligram figure derived from body weight, and not a range that extends upward.

The buccal route: a real trial that never publishes its own dose

One frequently cited human study tested a dissolve-in-mouth glutathione lozenge in 30 Filipino women for eight weeks and reported "a significant decrease in melanin indices from baseline to endpoint that became evident in as little as two weeks," with "no serious adverse events" and normal laboratory findings throughout⁶. Two things about it belong in any dosage discussion. First, it is open-label and single-arm by its own title — no control group and no blinding, so it cannot separate a drug effect from expectation. Second, and specific to this article's question: its published abstract states only that participants "received a glutathione-containing lozenge daily for eight weeks" and never states how much glutathione the lozenge contained. The route is documented; the dose is not.

The intranasal route: the one dose-ranging trial, and the one concrete adverse event in this literature

Glutathione nasal sprays are sold across this compound's market, and there is a genuine, well-designed dose-ranging trial behind that route — a Phase IIb, double-blind, placebo-controlled study in 45 people with Parkinson's disease, "randomized to receive intranasal placebo (saline), 100 mg GSH, or 200 mg GSH thrice daily for three months," followed by a one-month washout⁷. Its result is instructive in both directions. The high-dose group improved on total UPDRS (-4.6, P = 0.0025) and on the motor subscore (-2.2, P = 0.0485) versus its own baseline — but, in the paper's own words, "neither treatment group was superior to placebo," because the placebo arm improved too, and did so more robustly than the authors expected.

The same results section carries the single most concrete adverse event reported anywhere in the human glutathione literature this review located: "One participant in the high-dose GSH cohort developed cardiomyopathy." That is one case, in the 200 mg three-times-daily arm, in a 45-person trial. The paper does not assert that glutathione caused it, and neither does this article — but a dosage page that quotes this literature's benign safety language without also reporting its one serious event would be selectively summarizing.

The inhaled route: the largest and longest glutathione dosing trial ever run, and it was null

The best-powered glutathione dose study located by any route is not about skin or antioxidants at all. A randomized, double-blind, placebo-controlled, multicenter trial gave 153 cystic fibrosis patients aged 8 and older either "646 mg glutathione in 4 ml (n = 73) or placebo (n = 80) via an investigational eFlow nebulizer every 12 hours for 6 months"⁸. It is the highest sustained dose, over the longest period, in the largest sample, in this compound's published record.

It failed its primary endpoint. Lung function "was not different between the glutathione group and the placebo group over the 6-month treatment period" (P = 0.180), with no reduction in pulmonary exacerbations and no better quality-of-life scores. The mechanistic finding matters even more for a dosing discussion: glutathione was demonstrably delivered — "increased glutathione and metabolites in sputum demonstrated significant delivery to the lungs" — and yet "there was no indication of diminished oxidative stress to proteins or lipids, and no evidence for anti-inflammatory or antiproteolytic actions." Delivering more glutathione to the target tissue did not produce the antioxidant effect the entire supplementation rationale rests on. On safety, "the adverse event incidence was similar between glutathione and placebo."

Why there is no glutathione dosing chart on this page

The regulatory picture, re-checked

A live DailyMed structured-product-label search for "glutathione" returns 57 results, re-verified for this article on 2026-08-07 and unchanged: homeopathic combination remedies listing glutathione among a dozen ingredients, cosmetic soaps, creams and serums listing it as one ingredient among several, and BSS Plus — a genuinely FDA-approved product, but an ophthalmic surgical irrigation solution in which glutathione is a stabilizing component, not a therapeutic antioxidant given to a patient by injection⁹. There is no FDA-approved therapeutic glutathione drug product, which means there is no agency-reviewed label anywhere carrying a dose, a frequency, a maximum, or a monitoring instruction for the injectable form.

What this means if you're looking for a glutathione dose

The honest summary, kept attached to its routes: oral glutathione has a genuine randomized dose record at 250 mg once daily, 250 mg twice daily, and 500 mg daily, with a well-designed six-month trial showing 250 and 1,000 mg/day raise body glutathione stores in a dose- and time-dependent way that reverses within a month of stopping. Intranasal glutathione has one dose-ranging trial at 100 and 200 mg three times daily where neither dose beat placebo and one participant on the high dose developed cardiomyopathy. Inhaled glutathione has the largest and longest trial in the literature at 646 mg twice daily for six months, and it missed its primary endpoint despite confirmed delivery to the target tissue. And the IV route — the one most of this board's sellers actually ship — has exactly one randomized dose ever published (1,400 mg three times weekly, in Parkinson's disease, with no significant benefit), a 2025 systematic review calling the route contraindicated, and a national regulator's public warning against its cosmetic use on the record.

For the efficacy side of the same question, including how N-acetylcysteine gets marketed as if it were glutathione, see our glutathione evidence review. Glutathione's most common cross-sell on this site's boards has a differently shaped but equally specific dosing gap — see our NAD+ dosage article and its evidence review. For a third compound whose only published dose figures come from cell culture and animals rather than people, see our GHK-Cu dosage article. And for the same non-recommendation method applied across this site's peptide coverage, see our BPC-157 dosage article.