Evidence Trace, complete trial record

In plain terms

In plain terms: Glutathione (Oral) shows early signals in human research but the evidence is limited -- small trials, surrogate endpoints, or not yet independently replicated. It is an emerging area, not yet a proven one.

Glutathione (Oral)

C Limited: small, mixed or unreplicated trials

Category Supplements

Evidence RCTs (small, mixed)

Reviewed July 2026

PMIDs 24791752 · 21875351 · 33740389 · 28853742

The endpoint this grade is based on: Surrogate biomarker endpoint, Blood glutathione stores, where one 6-month trial of standard oral glutathione found a rise and one 4-week placebo-controlled trial found none; oxidative stress markers, where the placebo-controlled trials that measured them as primary endpoints were null. Mixed small trials, and oral absorption remains debated.

The evidence as the record states it

Evidence record

PMID 24791752 PMID 21875351 PMID 33740389 PMID 28853742

Richie et al. (Eur J Nutr, 2015; PMID 24791752): randomized double-blind placebo-controlled trial, 54 non-smoking adults, 250 or 1,000 mg/day standard oral glutathione for 6 months; blood, erythrocyte, plasma and lymphocyte glutathione rose 30 to 35 percent at the high dose, the oxidized-to-reduced ratio fell, and natural killer cytotoxicity rose; funding is not stated in the indexed record, and an ingredient maker lists this as its study, so the trial is not called independent here. Against: Allen and Bradley (J Altern Complement Med, 2011; PMID 21875351): randomized double-blind placebo-controlled trial, 40 healthy adults, 1,000 mg/day for 4 weeks, NIH-funded; no change in urinary F2-isoprostanes or 8-OHdG, the primary endpoints, and no change in erythrocyte glutathione, oxidized glutathione or their ratio. Søndergård et al. (Appl Physiol Nutr Metab, 2021; PMID 33740389): randomized double-blind placebo-controlled trial, 20 obese adults with and without type 2 diabetes, 1,000 mg/day for 3 weeks; whole-body insulin sensitivity by clamp improved, muscle glutathione rose numerically without a change in the redox ratio, and no oxidative stress marker changed. Form: Sinha et al. (Eur J Clin Nutr, 2018; PMID 28853742) is a 12-person uncontrolled pilot of liposomal glutathione funded by a company that sells liposomal glutathione; a different form, and it cannot carry a grade. Grade C: mixed small trials on biomarker endpoints.

PMID 24791752 PMID 21875351 PMID 33740389 PMID 28853742

Why Grade C and not Grade B

Grade C reflects early or limited human evidence -- small trials, surrogate endpoints, or preliminary findings not yet independently replicated. The evidence points in a promising direction but does not yet meet the standard for Grade B. A single well-powered, independently replicated trial with a meaningful endpoint would move this to Grade B or higher.

What this grade covers and what it does not

Grade C. One 6-month trial found standard oral glutathione raised blood stores; one 4-week placebo-controlled trial found no change in glutathione status or oxidative stress markers; a 3-week trial found better insulin sensitivity and no change in oxidative stress markers. Mixed small trials, not a replicated signal. WHAT THIS GRADE DOES NOT COVER: liposomal glutathione, where the only human study is an uncontrolled seller-funded pilot; intravenous glutathione; and any clinical outcome, which no trial measured.

What would move this grade

A well-powered randomized trial with an objective, clinically meaningful primary endpoint and at least one independent replication would support Grade B or higher.

How to track whether this is working Serum glutathione (reduced/oxidized ratio) at baseline and 12 weeks: liposomal or acetylated forms are required for meaningful oral absorption. Oxidative stress markers (8-isoprostane, 8-OHdG) at baseline and 8 weeks if available. Standard oral glutathione has very low bioavailability; The product uses a delivery technology that the positive trials relied on.