GHK-Cu: strong topical data, much weaker injectable evidence

GHK-Cu is one of the few copper peptides with actual human evidence, but almost all of it is topical and cosmetic. The skin-firmness and fine-line studies are real, if small. The systemic injectable claims people repeat are a different thing entirely and rest mostly on in-vitro and animal work.

The mental model I use: topical GHK-Cu is around Tier 2 for cosmetic endpoints, while injectable systemic GHK-Cu sits closer to Tier 3 or 4. Treating the topical evidence as if it validates injecting it is the common mistake.