Glutathione research: mechanism, findings and study quality

What it is

Glutathione (gamma-L-glutamyl-L-cysteinyl-glycine) is a three-amino-acid peptide made inside nearly all human cells, where it is the main low-molecular-weight thiol antioxidant. Because the body already makes it, most research asks a delivery question: does glutathione given from outside raise levels in blood and tissues, and does that change any outcome? The answer in published trials appears to depend on the route, so the findings below are grouped by route.

Mechanism of action

Glutathione joins glutamate to cysteine through the glutamate side-chain (gamma) carboxyl group rather than the usual peptide bond, a linkage that resists most peptidases. Cells build it in two ATP-dependent enzyme steps. The working part is the thiol group on cysteine: it donates electrons to neutralize reactive oxygen species, either directly or as the substrate of glutathione peroxidases, and glutathione S-transferases attach it to reactive compounds and drug metabolites so they can be cleared. The ratio of reduced (GSH) to oxidized (GSSG) glutathione is widely used as a marker of cellular redox state. For supplementation the central issue is delivery: glutathione swallowed as a capsule may be broken down in the gut before it is absorbed, which is why researchers have tested liposomal, intravenous, inhaled, intranasal and topical forms. In skin, glutathione is proposed to steer pigment production away from dark eumelanin, the rationale for skin-lightening studies.

What it’s most studied for

Research on supplemental glutathione falls into three groups. The first asks whether oral or liposomal forms raise glutathione in blood and cells of healthy adults, and whether oxidative stress or immune markers change as a result. The second tests routes that bypass the gut in populations where oxidative stress is thought to play a role: intravenous and intranasal glutathione in Parkinson's disease, and inhaled glutathione in cystic fibrosis. The third is cosmetic. Arjinpathana and Asawanonda (2012) gave 60 medical students 500 mg/day orally or placebo for four weeks and found significantly larger melanin reductions than placebo at only two of six skin sites. The trials summarized here measured biomarkers, lung function, motor scores and skin pigment rather than aging outcomes.

Notable findings

Each finding carries the species or population it was observed in and the dose that study used. Doses are reported as research context, exactly as published. They are not guidance.

Humans Randomized, double-blind, placebo-controlled trial (n=54)

Oral: six-month trial of body stores

Richie et al. (2015) gave non-smoking adults oral glutathione or placebo for six months and measured glutathione in whole blood, red cells, plasma, lymphocytes and cheek (buccal) cells. At six months the high-dose group showed increases of 30 to 35% in red cells, plasma and lymphocytes and 260% in buccal cells; increases were dose- and time-dependent and returned to baseline after a one-month washout. Natural killer cell cytotoxicity in the high-dose group was more than twice that of placebo at three months. The trial was supported by Kyowa Hakko Bio, which makes the glutathione product tested.

Dose studied: 250 mg/day or 1,000 mg/day orally for 6 months, then a 1-month washout (non-smoking adults)

[1] Richie JP Jr et al. · 2015 · PMID 24791752 ↗

Humans Randomized, double-blind, placebo-controlled trial (n=40)

Oral: four-week trial finds no change

Allen and Bradley (2011) randomized 40 healthy adults to oral glutathione or placebo for four weeks; 39 completed the study. Changes in the primary outcomes, urinary F2-isoprostanes and 8-hydroxy-2'-deoxyguanosine (markers of oxidative damage to lipids and DNA), did not differ between groups, and red blood cell glutathione, oxidized glutathione and their ratio also showed no change. The shorter duration is one possible reason this result differs from the six-month Richie trial.

Dose studied: 500 mg orally twice daily for 4 weeks (healthy adults)

[2] Allen J and Bradley RD · 2011 · PMID 21875351 ↗

Humans Randomized, double-blind, placebo-controlled pilot (n=21)

Intravenous: Parkinson's disease pilot

Hauser et al. (2009) randomized 21 people with Parkinson's disease whose motor symptoms were not adequately controlled by their medication to intravenous glutathione (11) or placebo (10). Later reviews of the trial describe the infusions as well tolerated and report no statistically significant improvement in Unified Parkinson's Disease Rating Scale (UPDRS) scores compared with placebo. With 21 participants over four weeks it was a pilot, not an efficacy trial.

Dose studied: 1,400 mg intravenously three times a week for 4 weeks (adults with Parkinson's disease)

[4] Hauser RA et al. · 2009 · PMID 19230029 ↗

Humans Randomized, double-blind, placebo-controlled phase IIb trial (n=45)

Intranasal: phase IIb Parkinson's trial

Mischley et al. (2017) randomized 45 people with Hoehn and Yahr stage 1 to 3 Parkinson's disease to intranasal saline or one of two glutathione doses for three months, followed by a one-month washout. All groups improved, placebo included. The high-dose group improved on total UPDRS (by 4.6 points) and the motor subscore relative to its own baseline, but neither glutathione group was superior to placebo. One participant in the high-dose group developed cardiomyopathy.

Dose studied: 100 mg or 200 mg intranasally three times daily for 3 months, then a 1-month washout; saline as placebo (adults with Parkinson's disease)

[5] Mischley LK et al. · 2017 · DOI 10.3233/JPD-161040 ↗

Humans Randomized, double-blind, placebo-controlled trial (n=153)

Inhaled: six-month cystic fibrosis trial

Griese et al. (2013) randomized people with cystic fibrosis aged 8 and older, with FEV1 of 40 to 90% of predicted, to inhaled glutathione (73) or placebo (80) for six months. Neither primary lung function endpoint differed between groups; an exploratory analysis found a 100 ml FEV1 advantage that was significant at three months but not later. Pulmonary exacerbations, patient-reported outcomes and airway markers of oxidation and inflammation did not improve, and the authors concluded that this dose produced no clinically relevant benefit.

Dose studied: 646 mg in 4 ml by eFlow nebulizer every 12 hours for 6 months (people with cystic fibrosis aged 8 and older)

[6] Griese M et al. · 2013 · PMID 23631796 ↗

Humans Randomized, double-blind, placebo-controlled split-face trial (n=30)

Topical: split-face trial in healthy women

Watanabe et al. (2014) had 30 healthy women aged 30 to 50 apply an oxidized glutathione (GSSG) lotion to one side of the face and placebo to the other. The melanin index was significantly lower on the glutathione side from early in the trial through week 10 (P<0.001 at 10 weeks), and the authors also reported improvements in other skin-condition measures. The trial tested the oxidized form, not reduced glutathione.

Dose studied: 2% GSSG lotion applied twice daily for 10 weeks, placebo lotion on the opposite side of the face (healthy women aged 30 to 50)

[7] Watanabe F et al. · 2014 · PMID 25378941 ↗

Study quality

Human data exist across several routes, but the trials are small and short, and their results conflict. For oral glutathione, a six-month, industry-supported trial (Richie et al. 2015, n=54) reported higher body stores, while a four-week trial (Allen and Bradley 2011, n=40) found no change; a liposomal pilot (Sinha et al. 2018) reported rises in blood and immune-cell glutathione but assessed only 12 people. The trials with disease endpoints, intravenous and intranasal glutathione in Parkinson's disease and inhaled glutathione in cystic fibrosis (the largest, n=153), did not outperform placebo on their primary measures. Skin trials are small and single-site, and the oral one found effects at only some sites. On safety, the intranasal Parkinson's trial reported one cardiomyopathy case in its high-dose group, and FDA linked at least 30 adverse events in 2026 to intravenous glutathione compounded from supplement-grade material with high endotoxin levels.

References

1
Richie JP Jr, Nichenametla S, Neidig W, et al. (2015). Randomized controlled trial of oral glutathione supplementation on body stores of glutathione. European Journal of Nutrition. PMID 24791752
2
Allen J, Bradley RD (2011). Effects of oral glutathione supplementation on systemic oxidative stress biomarkers in human volunteers. Journal of Alternative and Complementary Medicine. PMID 21875351
3
Sinha R, et al. (2018). Oral supplementation with liposomal glutathione elevates body stores of glutathione and markers of immune function. European Journal of Clinical Nutrition. PMID 28853742
4
Hauser RA, Lyons KE, McClain T, et al. (2009). Randomized, double-blind, pilot evaluation of intravenous glutathione in Parkinson's disease. Movement Disorders. PMID 19230029
5
Mischley LK, et al. (2017). Phase IIb study of intranasal glutathione in Parkinson's disease. Journal of Parkinson's Disease. DOI 10.3233/JPD-161040
6
Griese M, Kappler M, Eismann C, et al. (2013). Inhalation treatment with glutathione in patients with cystic fibrosis. A randomized clinical trial. American Journal of Respiratory and Critical Care Medicine. PMID 23631796
7
Watanabe F, et al. (2014). Skin-whitening and skin-condition-improving effects of topical oxidized glutathione: a double-blind and placebo-controlled clinical trial in healthy women. Clinical, Cosmetic and Investigational Dermatology. PMID 25378941
8
Arjinpathana N, Asawanonda P (2012). Glutathione as an oral whitening agent: a randomized, double-blind, placebo-controlled study. Journal of Dermatological Treatment. NCT01016080
9
US Food and Drug Administration (2026). FDA reminds compounders not to use dietary supplement grade glutathione for injectables. U.S. Food and Drug Administration.

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