Observed Side Effects (From Clinical Trials) In the Lancet 2021 Phase 2 trial (n=706), at the highest 4.5 mg/week dose, 88% of participants reported at least one side effect and 63% reported a GI-specific event
A change in eye color certainly merits attention and a visit to the eye doctor during adulthood
Moreover, elevated GSH levels can protect tumor cells by reducing the cytotoxic effects of several chemotherapy drugs, including cisplatin, doxorubicin, melphalan, and paclitaxel, ultimately leading to drug resistance [17]
So theres at least some possible risk here
Perhaps most importantly, GHK-Cu modulates matrix metalloproteinases, maintaining the balance between collagen production and degradation that characterizes youthful skin