Is oral glutathione absorbed?
Small studies split on whether swallowed glutathione reaches the blood. The results appear to track how long people took it and what each study compared against.
Contested (independent studies point both ways) · Low certainty (few, small, unrepeated studies) · 8 sources · ledger checked 22 Sep 2026 · every claim approved by the Longevity Circle evidence editor
In plain words
Nobody has shown that swallowing glutathione raises the amount in your blood in a way that lasts. One trial found a rise after six months at a high dose, and the rise was gone a month after people stopped. Other studies found no rise at all.
The short answer
Two of the three studies that measured blood levels after oral glutathione found no rise: a single 3 g dose in 7 people (1992) and a 4-week trial in 40 adults (2011). The third, a 6-month trial in 54 adults, found red blood cell levels 30 to 35% higher at 1,000 mg a day (2015). A 2024 meta-analysis pooled three randomised trials, two of them the 2011 and 2015 trials above, and found no significant rise; it adds no separate evidence. Certainty is low because the one positive result has never been repeated in small studies whose abstracts do not say who paid for them.
Where the evidence sits
| No rise in blood levels | Rise in blood levels |
|---|---|
| ■ Absorption study, 1992 · 7 people · one dose | ■ Randomised trial, 2015 · 54 people · 6 months |
| ■ Randomised trial, 2011 · 40 people · 4 weeks | □ Practitioner, 2017 · re-reads the 2015 trial |
| ◪ Meta-analysis, 2024 · pools trials listed here | |
| □ Science outreach, 2017 · argument, no data |
■ measured blood levels · ◪ re-analysed measurements already counted · □ argued or re-interpreted, no new data
Who says what
| Source | Finding | Design | People | Dose and length | Funding and independence |
|---|---|---|---|---|---|
| Witschi et al., 1992 | No rise in plasma | Single-dose absorption study | 7 | About 3 g once, blood sampled for 4.5 hours | Not stated |
| Allen & Bradley, 2011 | No change in red blood cell glutathione | Randomised, placebo-controlled | 40 | 500 mg twice a day for 4 weeks | Not stated |
| Richie et al., 2015 | 30 to 35% rise at the high dose | Randomised, placebo-controlled | 54 | 250 or 1,000 mg a day for 6 months | Not stated in the abstract |
| JCST meta-analysis, 2024 | No significant rise when three trials are pooled | Systematic review and meta-analysis | Pooled | Mixed | Not stated; cites the 2011 and 2015 trials |
| McGill OSS, 2017 | Cannot be absorbed | Argument from chemistry | None | None | University science outreach |
| Masterjohn, 2017 | Can be absorbed intact | Practitioner commentary | None | Cites the 2015 trial | Re-reads Richie et al., not new data |
Does glutathione survive digestion?
McGill University's Office for Science and Society made the skeptical case in 2017. Its argument is about chemistry, not a measurement:
The problem is that glutathione itself cannot be taken orally. It is composed of three amino acids linked together into a “tripeptide” and is easily broken down during digestion.
Pharmacologists at the University of Bern had measured it 25 years earlier. Seven healthy volunteers swallowed one dose of about 3 g, and the team drew blood for four and a half hours afterwards:
the concentrations of glutathione, cysteine, and glutamate in plasma did not increase significantly, suggesting that the systemic availability of glutathione is negligible in man
What happened when people took it for weeks or months?
At Bastyr University in 2011, 40 healthy adults took 500 mg twice a day or a placebo for four weeks. Glutathione inside their red blood cells did not move:
Total reduced, oxidized, and ratio measures of GSH status were also unchanged.
The Penn State trial of 2015 gave 54 non-smoking adults 250 mg or 1,000 mg a day, or a placebo, for six months:
At 6 months, mean GSH levels increased 30-35 % in erythrocytes, plasma and lymphocytes and 260 % in buccal cells in the high-dose group (P < 0.05).
Terms: erythrocytes are red blood cells. Buccal cells line the inside of the cheek.
The same abstract reports that the gain did not survive a month off the supplement:
In most cases, the increases were dose and time dependent, and levels returned to baseline after a 1-month washout period.
Chris Masterjohn, a nutrition writer, reads the 2015 trial as proof of absorption, though his commentary adds no new data. The 2024 meta-analysis found no significant rise across the trials it pooled, then qualified its own result:
However, higher doses and longer durations of supplementation may potentially lead to increased glutathione levels in the body.
Were the trials measuring the same thing?
The Bern volunteers took about 3 g once, the Bastyr group 1,000 mg a day for four weeks, and the Penn State group up to 1,000 mg a day for six months. The comparisons differ too. The 2011 trial set its glutathione group against its placebo group, while the 2015 abstract reports rises against each person's starting level, including at one month:
GSH levels in blood increased after 1, 3 and 6 months versus baseline at both doses.
A rise against baseline at one month and no difference against placebo at four weeks can both be true at once. The 2015 abstract does not say whether the one-month rise was also larger than in the placebo group.
What about liposomal and sublingual glutathione?
Each form has one small study reporting higher blood levels, and in each case a company selling the product is tied to the research. In Sinha et al., 2018, 12 adults took liposomal glutathione at 500 or 1,000 mg a day for a month with no placebo group, and levels rose within one to two weeks; Researched Nutritionals, which sells liposomal glutathione, funded the study, and the Penn State group behind the 2015 trial ran it. In Schmitt et al., 2015, 20 adults with metabolic syndrome tried the sublingual form and ordinary oral glutathione for three weeks each, and plasma levels were higher on the sublingual form; two of the four authors work for Laboratoires Le Stum, which makes it.
What would settle it
An independent trial of oral glutathione at 1,000 mg a day for at least six months, reporting red blood cell and plasma levels against placebo at 1, 3 and 6 months, with a washout period and a pre-registered analysis. A matching result from a second research group would raise the certainty from low to moderate.
How this page was made
The 8 sources are the 5 landmark studies found by a citation-ranked search of Europe PMC, the 2024 meta-analysis, and two commentaries (McGill and Masterjohn). Five further studies from the search were left out because they tested precursors (cysteine, glycine or NAC) or animals. Every claim was copied word for word from its source into the Longevity Circle ledger and checked against the original text, and a person approved each one. "Contested" means independent studies point in both directions; certainty follows the GRADE levels used in medical reviews. Drafting was assisted by AI.
Changelog: 22 Sep 2026, first version, 8 sources.