GHK-Cu has two human randomized trials in 34 years. Both tested topical creams, and both were negative on every objective skin measurement. The full record.

The copper-toxicity record for GHK-Cu is mixed and mostly reassuring in cell studies. It is also almost entirely silent, because no human has been studied outside the skin.

Every human hair study involving GHK or GHK-Cu tested a mixed formulation with other active ingredients. No single-agent human hair study is indexed in PubMed.

The expansive gene-expression claims about GHK trace to reviews sharing one company address. The only independent primary study is a 2012 computational screen.

What published work reports about the copper in GHK-Cu: bound copper versus free copper salts, the biphasic curve, and where the peptide may not be the active part.

A plain-language review of the published GHK-Cu inflammation literature: which studies used cells, which used mice, which used zebrafish, and what each one found.