Where the GHK-Cu study amounts went
The nose, a patch of removed skin and a cell-culture dish offer very different access. An experimental amount means little to me until its route is clear.
Intranasal GHK in mice
The aged-mouse experiment gave free GHK through the nose at 15 mg/kg daily for eight weeks. The 5xFAD mouse experiment used 15 mg/kg three times weekly for twelve weeks. Both reported better maze performance.
These are the authors' animal-study regimens. Intranasal delivery was used for access to the nervous system; the results establish neither blood-brain-barrier crossing in people nor an effective human amount. The missing distribution data prevent a straight translation into a human regimen.
Copper in removed human skin
In the skin-penetration experiment, the investigators measured copper after applying a GHK-Cu preparation to excised human skin. Over 48 hours, 136.2 ± 17.5 µg/cm² permeated dermatomed skin and 97 ± 6.6 µg/cm² remained as a depot. The reported permeability coefficient was 2.43 ± 0.51 × 10^-4 cm/h.
These measurements describe copper. They do not establish that intact GHK-Cu arrived at a living hair follicle or that the retained amount made skin firmer. The assay's focus on copper spoiled my hope of a tidy answer about intact peptide delivery.
The 2025 topical review describes free GHK's affinity for water and its poor passage through the oily outer skin barrier. Investigations of lipid attachments, liposomes and microneedles are attempts to solve access. Their early delivery results have yet to identify a proved human treatment regimen.
Free GHK in rat blood
The 1997 chromatography study followed GHK and its breakdown product, histidyl-lysine, in rat plasma after intravenous administration. It documented rapid metabolism of the free peptide. The assay could detect GHK at 50 ng/mL and histidyl-lysine at 15 ng/mL.
Those last figures describe detection limits. They supply no human half-life. A copper complex also requires its own account of absorption, distribution and breakdown. Without those measurements in people, confidence in a systemic GHK-Cu schedule outruns the pharmacology.
Fibroblast concentrations
The fibroblast collagen study reported stimulation beginning between 10^-12 and 10^-11 M, with a maximum near 10^-9 M. M denotes molar concentration: how much of a substance is present in a volume of liquid. These were concentrations surrounding cultured cells.
A culture bath gives cells direct contact. Topical preparations and a peptide entering the bloodstream face other obstacles. My question is how much intact material reaches the intended tissue and for how long; a concentration printed beside a dish result cannot answer it.
No validated human GHK-Cu dose, schedule or systemic pharmacokinetic basis is established. GHK-Cu has no FDA- or EMA-approved drug indication.