glutathione works Vitamin C and supplementation: a review of their additive effects on exercise performance How Does Glutathione Work? |

clinical work used GHK-Cu in the ~0.1% topical range

And when peptides like those endorsed today were tested to see if they would enhance performance by increasing growth hormone secretion, they were shown to be largely ineffective

Yang JY, Jie Z, Mathews A, Zhou X, Li Y, Gu M, et al

Glutathione acts to inhibit the process of melanogenesis either by directly inhibiting the enzyme tyrosine kinase that catalyzes it, or indirectly by means of its antioxidant properties

High levels of extracellular glutamate can inhibit the transportation of cystine by system Xc , resulting in an imbalance in antioxidative homeostasis and the occurrence of ferroptosis [4, 63]