# GHK-Cu Dosage in the Research Literature: Concentrations and Routes > GHK-Cu dosage in the research literature: picomolar-to-nanomolar in vitro, ~0.05-2% topical, rodent IP and oral mg/kg ranges, and the unresolved human pharmacokinetic question. Research context only. The concentrations, routes and stability conditions used in published studies — research context only, never a human dosing recommendation. ## Concentrations used across study models GHK-Cu dosage in the literature spans many orders of magnitude because the routes and models differ. The framing here is strictly research context — what was administered to which model at which concentration. None of it is a human dosing recommendation, and the site offers none. In vitro, the fibroblast collagen-synthesis response runs from 10⁻¹² to 10⁻⁹ M, with onset between 10⁻¹² and 10⁻¹¹ M and a peak near 10⁻⁹ M — a picomolar-to-nanomolar window that is striking for how low it sits [1]. Topical cosmetic and clinical formulations sit around 0.05% to 2% (w/w) in creams, serums and gels [3]. Rodent systemic studies used intraperitoneal ranges from 0.2-20 µg/g/day in pulmonary models up to 2 and 20 mg/kg in silicosis work, with the bleomycin fibrosis study at 2.6, 26 and 260 µg/mL/day IP [7] and the DSS-colitis study at 20 mg/kg oral gavage daily [14]. The human hair-loss trial applied a 5-ALA + GHK complex topically at 50-100 mg/mL [4]. The gap between the in-vitro nanomolar window and the rodent milligram-per-kilogram doses reflects bioavailability, not contradiction: a concentration that works on cells in a dish must survive clearance and reach tissue to work in an animal. That gap is the central problem of GHK-Cu delivery and the reason topical formulation gets so much research attention [5][10]. ## Routes studied GHK-Cu has been delivered by many routes in research. Topical is the dominant one — creams, serums, liposomes, nano-lipid carriers, ionic-liquid microemulsions, wound dressings, hydrogels and nanofibers [6][10]. Rodent systemic work used intraperitoneal, intranasal, oral gavage, and intravenous or subcutaneous routes [7][14]. The topical route forms a dermal copper depot — about 97 ± 6.6 µg/cm² retained over 48 hours in a human penetration study — giving prolonged local availability [5]. Hair studies have also used intradermal and dermal-infusion delivery (microneedle or tattoo-machine application) to bypass the stratum corneum [4]. Native GHK-Cu penetrates poorly because free GHK is highly hydrophilic (clogP −2.24), which is why delivery-system design recurs throughout the dosing literature [6][13]. Each route answers a different research question. Topical and scaffold work targets skin and wound repair, where local action is the point [5]. Intraperitoneal, oral and intranasal rodent dosing probes systemic and central effects — fibrosis, colitis, cognition and anxiety — that topical application cannot reach [7][12][14]. The route, in short, is chosen to match the model, and a dose meaningful in one context says little about another. ## Half-life and pharmacokinetics No rigorous human pharmacokinetic half-life has been published for GHK-Cu. This is one of the clearest gaps in the record: there is no validated human Cmax, bioavailability or tissue-distribution figure for injectable or systemic use. The free tripeptide (340.38 Da) is rapidly cleared by plasma peptidases — a rat HPLC study documented rapid metabolism of GHK to the dipeptide histidyl-lysine (HK) after intravenous dosing, with detection limits of 50 ng/mL for GHK and 15 ng/mL for HK [11]. 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 [6]. Topical behavior is the better-characterized pharmacokinetic story. Application forms a dermal copper depot — about 97 µg/cm² retained over 48 hours — giving prolonged local availability that a plasma clearance figure does not capture [5]. In other words, the topical route turns a short-lived molecule into a slow-release local reservoir, which is part of why the dermatologic evidence is the strongest in the literature [5]. There are no completed Phase 2/3 trials for systemic or injectable GHK-Cu — a topical wound-healing trial has been registered — and community-circulated injectable protocols have no peer-reviewed pharmacokinetic basis [6]. ## Stability, formulation and what destabilizes the complex The GHK-Cu complex has a very high copper stability constant (log K approximately 16.44), far higher than free GHK, which limits pro-oxidant free-copper release [9]. It is most stable near pH 5-6.5 at a 1:1 copper-to-peptide ratio. The blue-violet color of a reconstituted solution is the expected Cu(II) d-orbital absorption and indicates an intact complex; a shift to brown or green indicates oxidation or precipitation [9]. Strong reducing agents break it. Ascorbic acid below about pH 3.5 reduces Cu(II) and destroys the complex, and AHAs and BHAs at low pH can destabilize it or compete for copper [6]. This is the basis of the well-known vitamin-C incompatibility, and it is a genuine formulation and user-error risk: combine the two and both actives can be lost [6]. For improving delivery, several strategies appear in the research record. Liposomal encapsulation reached 31.7% (anionic) and 20.0% (cationic) loading efficiency and stayed stable for four weeks at room temperature [10]. Palmitoylation raises lipophilicity (Pal-GHK clogP approximately 1.14 versus free GHK's −2.24), and ionic-liquid microemulsions and microneedle pretreatment offer further routes past the stratum corneum, with about 134 nmol GHK permeating under microneedling versus none through intact skin [13]. The blue color, in short, is the instrument reading: intact complex while blue, compromised once it turns. --- A dusk reading room for the GHK-Cu copper-tripeptide record — every collagen study, gene-expression map, and hair-count trial read under one neon horizon, held by no clinic and sold by no one.