# GHK-Cu Research Dosing Context: Concentrations, Routes, Stability > GHK-Cu research dosing context: the picomolar-to-nanomolar fibroblast range, topical 0.05-2% formulations, rodent study doses, the copper-stability constant, and why no validated human pharmacokinetic half-life exists. Research framing only. What concentrations were studied, by which route, in which species, and what the literature does and does not establish about half-life and stability. This page describes research, not a personal protocol. ## How GHK-Cu was dosed in research GHK-Cu research dosing spans a wide range because the studies span cell culture, topical skin, and rodent systemic models, and the units are not interchangeable across those settings. The foundational fibroblast work used 10^-12 to 10^-9 M in culture medium, with collagen synthesis starting at 10^-12 to 10^-11 M and peaking near 10^-9 M [1]. Topical cosmetic and clinical formulations generally run about 0.05% to 2% (w/w) in creams, serums, and gels [2]. Rodent systemic studies used much larger amounts by intraperitoneal, intranasal, and oral-gavage routes, and the strongest human topical hair trial applied a 5-ALA + GHK complex at 50 to 100 mg/mL [7]. A molar concentration in a fibroblast dish, a percentage in a cream, a milligram-per-kilogram in a mouse, and a milligram-per-milliliter on a scalp are four different kinds of number, and collapsing them into a single human figure is exactly the error this page is written to avoid. None of these numbers is a human dosing instruction; they are the concentrations and routes that specific studies administered to specific models. This page is the [research dosing context](/dosage) referenced elsewhere on the site. ## Concentrations and routes studied The studied routes are topical (cream, serum, liposome, nano-lipid carrier, hydrogel, nanofiber), intraperitoneal (rodent systemic), intranasal (rodent cognitive), oral gavage (rodent colitis), intravenous and subcutaneous (rodent pharmacokinetic), and intradermal delivery (microneedle in hair studies). Concrete examples from the rodent literature include intraperitoneal mouse emphysema dosing at 0.2, 2, and 20 ug/g/day on alternate days; intranasal aging/cognition work at 15 mg/kg; and rat behavioral studies in the roughly 0.5 ug/kg to 0.5 mg/kg intraperitoneal range [14]. The most reproducible human-relevant route is topical, where GHK-Cu forms a dermal copper depot of about 97 ug/cm^2 retained over 48 hours [9]. Systemic injectable protocols circulated in community settings have no peer-reviewed human pharmacokinetic basis [9]. ## Half-life and the missing human pharmacokinetics 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 histidyl-lysine after intravenous dosing, with detection limits of 50 ng/mL for GHK and 15 ng/mL for HK [13]. Secondary literature cites a short systemic elimination half-life on the order of 1 to 2 hours, with the copper-chelated complex more stable than free GHK, but those are estimates, not validated human values [13]. Topically the picture inverts: rather than a fast systemic clearance, application forms a long-lived local copper depot (about 97 ug/cm^2 retained over 48 hours), which is why most human evidence is topical [9]. The absence of validated human PK is one of the clearest limits in this entire literature. ## Stability and formulation rules The GHK-Cu complex has a very high copper stability constant (log K of about 16.4), far higher than free GHK, which limits pro-oxidant free-copper release [6]. It is most stable near pH 5 to 6.5 at a 1:1 copper-to-peptide ratio, and the blue-violet color of a reconstituted solution is the expected Cu(II) absorption signature of an intact complex, whereas brown or green shifts indicate oxidation or precipitation. Strong reducing agents, especially ascorbic acid below about pH 3.5, reduce Cu(II) and break the complex, and AHAs and BHAs and other low-pH actives can destabilize it or compete for copper [15]. Free GHK is highly hydrophilic (clogP -2.24), limiting passive penetration, so palmitoylation (Pal-GHK, clogP about 1.14), liposomal encapsulation, ionic-liquid microemulsions, and microneedle pretreatment are the documented delivery enhancements [15]. ## What the dosing literature does not establish The most important thing the dosing literature does not establish is a human systemic protocol. There is no validated human pharmacokinetic profile (no measured half-life, Cmax, bioavailability, or tissue distribution) for injectable or systemic GHK-Cu, and the rodent and secondary-literature estimates of a 1-to-2-hour elimination half-life cannot stand in for that [13]. The rodent systemic doses summarized above span emphysema, fibrosis, colitis, and cognition models across intraperitoneal, oral, and intranasal routes, and they are not convertible into a human dose by any rigorous method [6]. Topical exposure is the only route with a reproducible human-relevant measurement, namely the dermal copper depot of about 97 ug/cm^2 retained over 48 hours [9]. For the safety questions that follow from these gaps, see [GHK-Cu side effects and safety](/faq). The framing throughout this page is research context, never an instruction for any person. --- The GHK-Cu copper-peptide record, read with each finding labelled by how much it can bear — established, limited, context, or safety — and legible to every reader; no clinic, no counter, nothing here to sell.