GHK-Cu: why the powder is blue and what copper peptide means

GHK-Cu is the tripeptide glycyl-histidyl-lysine holding one copper(II) ion. The copper is what makes it blue, what makes it a different molecule from GHK, and what its two INCI names are about. Status as of September 2026.

By Touchstone PeptidesSeptember 22, 20265 minute read

GHK-Cu is a three-residue peptide, glycyl-L-histidyl-L-lysine, holding one copper(II) ion. The peptide on its own is GHK; add the copper and you have a coordination complex with a different mass, a different CAS number, a different INCI name and a blue-violet colour. The colour comes from the copper, not the peptide. It is an INCI-listed cosmetic ingredient, not an FDA-approved drug, and its 503A status splits by route.

What GHK is

GHK was reported in 1973 by Loren Pickart as a tripeptide isolated from human serum (Nature New Biology). Its sequence is Gly-His-Lys, three of the twenty coded amino acids, with a free N-terminal amine and a free C-terminal acid. PubChem CID 73587 gives C14H24N6O4 and an average molecular weight of 340.38; CAS 49557-75-7. The INN for the copper-free peptide is prezatide, and its INCI name, as listed among PubChem's synonyms, is Tripeptide-1.

Three residues is short enough that the whole molecule is essentially its side chains: a histidine imidazole ring in the middle and a lysine chain ending in a positively charged ammonium group. The imidazole is the part that matters for copper. Our what a peptide is piece covers the vocabulary, and the two-residue peptides shows how little chain a molecule needs to count as one.

What "copper peptide" means

A "copper peptide" is a peptide that has chelated a copper ion: the metal is held by several donor atoms from the peptide at once, the way a hand holds a ball, rather than sitting loose beside it as a salt would. In GHK-Cu the copper(II) ion is bound in solution by three nitrogen atoms: the terminal amino group of glycine, the deprotonated amide nitrogen of the Gly-His peptide bond, and the imidazole nitrogen of histidine. That arrangement was worked out by optical, EPR and electron spin-echo spectroscopy in 1982 and confirmed by X-ray and solution structures in 2011. The fourth position around the copper is labile: in the solid state it is filled by a carboxylate oxygen, and in the crystal the complex forms oxygen-bridged copper pairs that do not persist in solution.

That is why GHK-Cu is written as a distinct substance rather than "GHK plus copper". PubChem CID 71587328 gives it the formula C14H23CuN6O4+ and an average molecular weight of 402.92; CAS 89030-95-5; INN prezatide copper; INCI name Copper Tripeptide-1. The formula has one hydrogen fewer than GHK because the amide nitrogen loses its proton when it binds the metal. The lysine ammonium stays charged, which is why the complex carries a positive charge and, as a solid, comes with a counter-ion such as acetate or chloride.

The vial we stock as GHK-Cu is listed at molecular weight 402.92 and CAS 89030-95-5, which is the copper complex. A certificate for it should show the peptide identity by mass spectrometry and, ideally, a copper content, because purity of the peptide chain says nothing about whether the copper is there in the right proportion; purity is not potency.

Why the powder is blue

Copper(II) has nine electrons in its d orbitals. When nitrogen atoms surround the ion in a square arrangement, those orbitals split into slightly different energies, and the ion can absorb a photon of visible light to move an electron between them. For copper bound to nitrogen donors that absorption falls in the orange-to-red part of the spectrum, so the light that is not absorbed, the blue and violet, is what reaches the eye. Chemists call these d-d transitions. Copper-free GHK has no d electrons to excite and is a white to off-white solid.

The colour is therefore a quick identity check, not a quality mark. A blue-violet powder tells you copper is present in a nitrogen-bound environment; it does not tell you how much, or whether the peptide is intact. Loose copper salts are also blue. Only the certificate settles the ratio.

Why it takes up water

GHK-Cu is a small, highly polar molecule: a charged complex with a free ammonium group, several hydrogen-bond donors and a counter-ion. Solids built from ions and polar groups draw water vapour out of the air and hold it in the lattice, so a lyophilized powder of this kind gains mass on exposure to humid air. The practical meaning for paperwork is that a gravimetric fill checked in a dry room and a fill checked after the vial has been open are different numbers, and that water content (Karl Fischer) and net peptide content belong on a certificate for this molecule; see net peptide content.

Cosmetic ingredient and research vial

Copper Tripeptide-1 is an INCI name, the naming system used on cosmetic labels worldwide, and the same molecule can be a cosmetic raw material or a research vial depending on how it is labelled and sold. Our cosmetic peptides sit on their own shelf; nothing there is sold as a cosmetic ingredient or with a cosmetic claim. The document pack a formulator needs is described in cosmetic-grade vs research-grade peptides.

Regulatory status as of September 21, 2026

FDA drug approval. There is no FDA-approved drug whose active ingredient is GHK-Cu.

503A category. GHK-Cu for all routes but one was removed from Category 1 on April 22, 2026 when its nominations were withdrawn; after one nominator clarified on May 5 that it meant to withdraw only a single route of administration, FDA's May 14 update says the entry "will be added back to category 1", and FDA intends to consult the Pharmacy Compounding Advisory Committee before the end of February 2027. Category 1 is not the bulks list and is not an approval; it means "under evaluation". The full sequence is in Category 1, Category 2 and the 503A bulks list.

The Category 2 entry for the excluded route, dated September 29, 2023, moved to "nominated but withdrawn" on April 22, 2026, and FDA's text for it is still on the page:

Compounded injectable drugs containing GHK-Cu may pose risk for immunogenicity due to the potential for aggregation and peptide-related impurities.FDA, bulk drug substances page, content current April 22, 2026

WADA. GHK-Cu is not named anywhere on the 2026 Prohibited List.

None of this changes what a research vial is: Category 1 describes what a licensed pharmacy may do, not research-use-only material.

Sources

For laboratory research use only. Not a drug, not a supplement, and nothing here is a claim about what any of this material does in a person or an animal.

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