GHK-Cu is a copper complex: a three-amino-acid peptide, glycyl-histidyl-lysine, wrapped around a copper ion. Because the copper is part of the molecule, a reasonable question follows from the name itself, which is how much copper a given amount of GHK-Cu actually carries, and whether that could ever approach the level at which copper becomes harmful.
The answer has two halves that come from different kinds of document. The copper content is chemistry, and can be worked out from molecular weights. The harm threshold is nutrition science, and comes from the upper intake level that the National Institutes of Health’s Office of Dietary Supplements publishes for copper [1]. The catch is that the second number was built for a different route than most GHK-Cu products use. What amounts studies have actually applied is a separate record, kept in GHK-Cu dosage.
How much of GHK-Cu is copper
A molecule’s weight is the sum of its atoms, so the share contributed by one copper atom is simply copper’s atomic weight, 63.546, divided by the weight of the whole complex. The complication is that “GHK-Cu” is not one fixed formula.
PubChem, the National Library of Medicine’s chemistry database, holds separate records for a complex with one peptide per copper ion [2], a complex with two peptides sharing one copper ion [3], and that two-peptide complex as an acetate salt [4]. Each carries the same single copper atom inside a different total weight, so the copper share differs by about a factor of two.
| Form (PubChem record) | Molecular weight | Copper share | Copper per 1 mg |
|---|---|---|---|
| One peptide per copper (prezatide copper) | 402.92 | 15.8% | 158 mcg |
| Two peptides per copper (bisprezatide copper) | 742.3 | 8.6% | 86 mcg |
| Two-peptide complex as acetate salt | 862.4 | 7.4% | 74 mcg |
For a reader, the practical consequence is that a milligram figure on a GHK-Cu label does not by itself say how much copper is present. The label would also need to name the form, and the same milligram amount of the 1:1 complex carries about twice the copper of the acetate salt.
What the copper upper limit is, and what it covers
The Office of Dietary Supplements lists a Tolerable Upper Intake Level, or UL, of 10,000 micrograms of copper a day for adults aged 19 and over, including during pregnancy and breastfeeding [1]. It defines a UL as the maximum daily intake unlikely to cause adverse health effects.
Two details in that fact sheet limit how far the number travels. The limits were set for copper from food and supplements, based on levels associated with liver damage. They also do not apply to people receiving supplemental copper under medical supervision [1]. The UL is a number about copper swallowed by healthy people, and the fact sheet gives no figure for copper absorbed through skin or given by needle.
10,000 mcg
Adult upper limit for copper per day, from food and supplements
NIH ODS
900 mcg
Adult recommended daily copper intake
NIH ODS
50–120 mg
Total copper in an average adult body
NIH ODS
For scale, the same fact sheet reports that adults aged 20 and over take in 1,400 to 1,700 micrograms of copper a day from food and supplements combined [1]. The fact sheet also notes that typical diets in the United States meet or exceed the recommended intake.
Putting the two numbers side by side
Dividing the upper limit by the copper per milligram gives the amount of each form that would contain 10,000 micrograms of copper: about 63 milligrams of the 1:1 complex, 117 milligrams of the two-peptide form, or 136 milligrams of the acetate salt. This is arithmetic about copper content, not a dose of GHK-Cu for anyone.
The one GHK-Cu strength tested against placebo in people shows how far typical topical amounts sit from that figure. A 1992 trial on venous leg ulcers used a tripeptide copper complex as a 0.4% cream [5], which is 4 milligrams of the complex in each gram of cream. The abstract does not name the form, so the copper per gram falls somewhere between about 295 and 631 micrograms, and that is the amount in the cream rather than the amount absorbed. In that trial, 86 evaluable patients completed treatment, and the copper cream did no better than placebo.
How much copper crosses skin
Whether copper on the skin reaches the bloodstream was measured only in the laboratory. A 2010 study applied a 0.68% aqueous copper tripeptide solution to human skin samples in diffusion cells for 48 hours [6].
Through dermatomed skin, 136.2 micrograms of copper permeated each square centimeter over the 48 hours, and 82 micrograms per square centimeter stayed in the tissue. Those figures come from excised skin under “infinite dose” conditions, in which the solution is never allowed to run out. They show that copper from the peptide can cross skin, but they cannot be scaled up to predict what a person absorbs from a serum. What topical use has shown on outcomes is set out in GHK-Cu topical vs injected.
How much GHK the body already makes
GHK is not foreign to the body. A 2018 review reports a plasma level of about 200 nanograms per milliliter at age 20, falling to 80 nanograms per milliliter by age 60 [7]. That is a concentration in blood, not a daily intake, so it cannot be set directly against the upper limit, but it shows the peptide circulates at trace levels without any product being used.
Copper bound to the peptide versus free copper salts
One laboratory study compared GHK-Cu with two simple copper salts, copper chloride and copper acetate, on human skin cells called keratinocytes [9]. At the same treatment concentrations, the two salts raised irritation markers such as IL-1α and IL-8 after 24 hours at 58 and 580 micromolar, while GHK-Cu was not cytotoxic and caused no significant change in those markers.
That is a cell-culture result, not a study in people, and it measured irritation rather than whole-body copper load. It does suggest that the form copper arrives in matters as much as the amount, which is the same lesson the molecular weights teach.
Where copper does become a concern
The fact sheet describes copper toxicity as rare in healthy people who do not have an inherited defect in copper handling [1]. Chronic high exposure can cause liver damage and stomach symptoms such as abdominal pain, cramps, nausea, diarrhea and vomiting.
The exception it names is Wilson’s disease, a rare inherited condition caused by a mutation in the ATP7B gene that stops the body clearing copper normally [1]. People with it have a high risk of copper toxicity, and no published study has tested GHK-Cu in them, so the general-population arithmetic above does not describe their situation. Reported reactions to GHK-Cu itself are collected in GHK-Cu side effects.
What this means
By weight, GHK-Cu is between about 7% and 16% copper, depending on the form. The 10,000-microgram upper limit corresponds to tens of milligrams of the complex, while a gram of the one placebo-tested cream held well under a milligram of copper before any question of absorption. The upper limit was never written for skin or injection, so the comparison bounds the question without settling it.
For other options with human data behind them, start at the recovery goal page.