Does oral glutathione work as well as injections?

Why the oral trials disagree

Glutathione is a three-amino-acid peptide that the body makes itself. The 1992 study gave 7 healthy volunteers one oral dose and measured plasma for 270 minutes: glutathione and its building blocks did not rise significantly, and the authors concluded that systemic availability is negligible, because enzymes in the gut and liver break it down. The 2015 trial instead gave 54 adults 250 or 1,000 mg a day for 6 months and found body stores rising over time, by 30–35% in red cells, plasma and lymphocytes at the higher dose.

The two designs measured different things, a single dose against months of daily intake, so they do not strictly contradict each other. Neither shows how a pill compares with an injected dose.

For what is reported about glutathione's adverse effects at these doses, see glutathione side effects.

Sublingual and oral-spray forms

A 2015 three-week crossover in 20 volunteers with metabolic syndrome found higher plasma glutathione with a sublingual form than with an oral one; two of its authors are affiliated with Laboratoires Le Stum. A 2019 pilot crossover in 15 healthy adults found a nano-sized solution held in the mouth raised red-cell glutathione more than placebo; three authors received funding from Pelame, LLC to perform it.

Inhaled and nasal forms

In a 2013 six-month trial in cystic fibrosis, inhaled glutathione reached the lungs but did not improve lung function (FEV1) against placebo. Intranasal glutathione in Parkinson's disease met safety and tolerability criteria in a 30-person trial, and in a 45-person phase IIb trial neither dose was better than placebo; one participant in the high-dose group developed cardiomyopathy.

What is not known

None of the trials above compared a pill with an injection, so the question in the title has no head-to-head answer in this record. What exists is evidence about each form on its own terms.