GHK-Cu

GHK is the tripeptide glycyl-L-histidyl-L-lysine, a fragment of human collagen that occurs naturally in plasma and declines with age. The biologically active form on skin and in tissue is the copper(II) complex GHK-Cu, where the imidazole and amine ligands chelate Cu²⁺. The complex appears to act through several coupled pathways: it modulates the expression of a broad set of genes involved in tissue remodeling, stimulates fibroblast collagen and glycosaminoglycan synthesis, supports angiogenesis through copper-dependent mechanisms, and exhibits anti-inflammatory and antioxidant effects in dermal and other connective-tissue contexts ([Pickart and Margolina, *Int J Mol Sci* 2018, 19(7):1987](https://doi.org/10.3390/ijms19071987)). Copper itself is a required cofactor for lysyl oxidase, the enzyme that cross-links collagen and elastin — which is part of why GHK-Cu's effects on skin density and elasticity are mechanistically plausible rather than merely empirical.

GHK-Cu sits at an unusual junction: it has both the deepest cosmetic adoption of any peptide on this site and a much richer preclinical literature than its dermatology reputation suggests. Topical GHK-Cu has been studied for photoaged skin since the 1990s, and several 12-week placebo-controlled trials in women with mild-to-moderate photoaging report increases in skin density, dermal collagen, and clarity, plus reductions in fine-line depth — including a 71-woman facial-cream study and a separate eye-cream comparison against vitamin K. These trials are smaller and shorter than the pivotal trials on this site's other peptides, but the consistent direction of effect across replications is what supports the strong cosmetic adoption rather than any one large RCT. The off-cosmetic literature has expanded substantially through Pickart's gene-expression work. The 2018 *International Journal of Molecular Sciences* review documents GHK's regulatory effects across genes involved in skin and lung tissue repair, DNA-damage response, neuroprotection, and several anti-cancer pathways. Most of this work is preclinical — fibroblast, keratinocyte, and animal models rather than human RCTs — but the breadth is unusual for a tripeptide and underwrites the practitioner interest in injectable GHK-Cu for wound healing, post-procedure skin recovery, and hair-follicle support. The injectable use case is where the evidence base thins out. There are no large RCTs of subcutaneous GHK-Cu for systemic indications. Most of the human evidence for systemic effect is topical or anecdotal. The other practical concern is the copper itself: the copper(II) ion is the active center, and excessive copper exposure carries real toxicity (Wilson's disease in chronic excess, GI symptoms acutely). This is the watch-point that distinguishes GHK-Cu from peptides that act through receptor pharmacology alone.