Scene 05 / The numbers
GHK-Cu dosage in research: the concentrations and routes the studies used.
What was administered, to which model, by which route — and where the human pharmacokinetic record simply does not exist.
Concentrations the studies used
GHK-Cu dosage in research is described as study concentrations and model protocols, never as a human regimen. The foundational in vitro range is precise: collagen synthesis in human fibroblasts began between 10^-12 and 10^-11 M and peaked near 10^-9 M, and notably without any change in cell number, which marks it as a specific metabolic effect rather than faster proliferation [1]. Topical cosmetic and clinical formulations sit at roughly 0.05% to 2% (w/w) in creams, serums, and gels. The controlled human hair trial used a 5-ALA + GHK complex at 50 and 100 mg/mL applied to the scalp over six months [4].
Rodent systemic studies span a wide dose range by design, because they probe different organs and endpoints. Mouse pulmonary models used intraperitoneal GHK at 0.2-20 ug/g/day; aging and cognition models used intranasal GHK at 15 mg/kg, daily or three times weekly; a colitis model used 20 mg/kg oral gavage; and behavioral studies used roughly 0.5 ug/kg to 0.5 mg/kg intraperitoneally [17][18]. These are model protocols, not translations to people — the species, route, dose, and endpoint are part of every number, and a concentration that drives a fibroblast in culture is not a dose anyone administered to a person.
Routes studied
The most-studied route by far is topical — creams, serums, liposomes, nano-lipid carriers, ionic-liquid microemulsions, wound dressings, and nanofibers. Topical application forms a measurable dermal depot: a human penetration study found a permeability coefficient of 2.43 x 10^-4 cm/h, with 136.2 ug/cm^2 of copper permeating over 48 hours and about 97 ug/cm^2 retained as a depot, giving prolonged local availability without systemic loading [5]. Rodent research adds intraperitoneal (systemic studies), intranasal (cognition), oral gavage (colitis), and intravenous or subcutaneous (pharmacokinetic) routes. Intradermal delivery via microneedle or tattoo-machine has been used in hair studies to bypass the penetration barrier.
Route matters more for GHK-Cu than for many peptides because the molecule's behavior changes with it. Free GHK is highly hydrophilic (clogP -2.24), so a topical dose largely stays where it lands unless a delivery system carries it deeper, while a systemic dose is cleared rapidly by plasma peptidases [12][16]. The research record is therefore deepest exactly where the molecule is best behaved — topical — and thinnest where it is hardest to characterize.
Half-life in the research record
No rigorous human pharmacokinetic half-life has been published for GHK-Cu. The free tripeptide (340.38 Da) is rapidly cleared by plasma peptidases: a rat HPLC study documented rapid metabolism of GHK to the dipeptide HK after intravenous dosing, with detection limits of 50 ng/mL for GHK and 15 ng/mL for HK [16]. Secondary literature cites a short systemic elimination half-life on the order of 1-2 hours, with the copper-chelated complex more stable than free GHK — but that figure is a secondary estimate, not a validated human measurement, and should be read as such.
Topical use is the exception to short systemic availability. The dermal copper depot — about 97 ug/cm^2 retained over 48 hours — gives prolonged local presence even as any systemic peptide clears quickly [5]. The two facts are not in tension: a molecule can be short-lived in plasma and long-resident in skin at the same time, which is exactly why the topical and systemic stories diverge so sharply in this literature.
Stability and handling in the research context
The GHK-Cu complex is most stable near pH 5-6.5 at a 1:1 copper-to-peptide ratio, where its high stability constant (log K ~16.4) keeps copper bound and limits pro-oxidant release [8]. The blue-violet color of a reconstituted solution is the expected Cu(II) d-orbital absorption and signals an intact complex; brown or green shifts indicate oxidation or precipitation. Strong reducing agents (ascorbic acid below ~pH 3.5) reduce Cu(II) and break the complex, and low-pH actives can destabilize it or compete for copper [12]. Because free GHK is highly hydrophilic (clogP -2.24), delivery strategies — palmitoylation, liposomal encapsulation, microneedle pretreatment — exist specifically to improve penetration [12].