glutathione injection skin lightening evidence for lightening: a regnant myth or evidence-based verity? Glutathione Skin Lightening - Revivify

It means the certainty is low

First, all the rats were anesthetized via an intraperitoneal injection of 2% pentobarbital sodium (75 mg/kg), and the hair of the right posterior leg was removed

Naturally occurring plasma levels of GHK were confirmed to decline from approximately 200 g/L at age 2025 to 80 g/L by age 6080, coinciding with reduced regenerative capacity

Consequently, FcRn rescues both albumin and IgG from intracellular lysosomal degradation, which explains their long plasma half-lives and high abundance in plasma

Spiller K, Xi ZX, Peng XQ, Newman AH, Ashby Jr CR, Heidbreder C et al (2008)

Advances in biotechnology have allowed manufacturers to optimize conditions such as nutrient levels, temperature, and pH to greatly increase the yields of glutathione from microorganisms such as yeast and bacteria