Glutathione is the body's main intracellular antioxidant and one of the best studied molecules in the whole of this space. PubMed carries well over twelve thousand records mentioning it, and unlike most compounds discussed here, its clinical literature is genuinely large.
That makes the finding below more interesting rather than less.
Forty-seven studies, and what they cover
ClinicalTrials.gov returns roughly 47 registered studies for glutathione injection. The phases distribute the way a real clinical portfolio does: about eleven Phase 2, six Phase 3, five Phase 1, four Phase 4, and a group registered as not applicable.
Read the titles and the pattern is clear. Chemotherapy-resistant ovarian cancer. Advanced hepatocellular carcinoma. Male infertility and a nutritional supplement combination. Oncology, hepatology, reproductive medicine.
Titles mentioning skin, whitening, lightening or pigmentation: about two out of forty-seven.
Why that matters for anyone searching a dosage chart
Search volume for glutathione injection is dominated by skin lightening. The registered clinical literature is dominated by cancer and organ disease.
So the number a chart quotes, if it came from a trial at all, was very likely established in a patient population being treated for something serious, by a route selected for that setting. It was not established for cosmetic use in a healthy person, because those studies largely do not exist.
The antioxidant framing is not a free pass
Glutathione being endogenous and physiologically important does not mean an injected bolus of it is well characterised for an arbitrary purpose. Endogenous does not mean unlimited, and a molecule that the body regulates tightly on its own is exactly the kind where an exogenous dose needs evidence rather than intuition.
Reading a chart for it
A glutathione injection dosage chart is honest when it names the study, the population and the route behind each figure, and says plainly which indications the literature does and does not cover.
The single check worth doing takes a minute: open the registry listing and read the titles rather than the count. Forty-seven looks like a settled field. Two on the question you are asking is the actual position.