The bioavailability of orally administered glutathione could be verified in some studies. Most likely a part of the absorbed tripeptide glutathione is broken down by stomach acid into the individual amino acids. However, studies have verified that after oral supplementation of GSH (reduced glutathione) the blood levels of glutathione increase. (Refer to article: GSH blood levels increase after oral intake). After oral GSH application, blood levels increased, but only by GSH administration and not by intake of single amino acids components. This is an argument against the thesis explaining the increase in the blood concentration of glutathione only by the individual amino acids, which the body again must synthesize to glutathione. Glutathione may also be absorbed already in the mouth. See also article: Glutathione Absorption in the Gastrointestinal Tract

Thus, the oral ingestion of glutathione is advisable.

For the application of S-acetyl glutathione refer to S-Acetyl Glutathione versus GSH