# GHK-Cu Dosage in Research: Concentrations, Routes, and Half-Life > GHK-Cu dosage in research: fibroblast effects at 10^-12 to 10^-9 M, topical formulations at ~0.05-2%, rodent IP and intranasal protocols, and why no validated human half-life exists. Research-context only. 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]. --- The GHK-Cu copper-peptide literature, read one scene at a time — collagen dose-response, hair-count trial, copper-stability chemistry, and the human-data gap, each logged to its study and nothing here dispensed.