GHK-Cu is the copper(II) complex of the tripeptide glycyl-L-histidyl-L-lysine. Unlike most research peptides, it is dosed through two separate routes with very different evidence behind them: a topical concentration expressed as a percentage, and a subcutaneous dose expressed in milligrams. Confusing the two is the single most common mistake, because 2 mg/mL is a normal topical strength and also a plausible injectable concentration, but they mean entirely different things in practice.
This guide separates both protocols, gives the exact syringe math for the common vial sizes, and explains why the copper component (not the peptide) is what actually limits how long you should run it.
Topical GHK-Cu Dosing
Topical is the route with published human skin data. Cosmetic and study formulations run 0.05 percent to 0.2 percent GHK-Cu, which translates to 0.5 mg/mL through 2 mg/mL. Applied once or twice daily to clean skin, that range covers essentially all of the published work on wrinkle depth, skin density, and photodamage.
To mix a topical solution from a standard 50 mg vial: adding 25 mL of bacteriostatic water gives 2 mg/mL, which is 0.2 percent, the top of the cosmetic range. Adding 50 mL gives 1 mg/mL (0.1 percent), a reasonable middle setting for a first run. Start at the lower concentration if you have reactive skin, since the copper complex can sting on freshly exfoliated or broken skin.
- 0.05 percent = 0.5 mg/mL, conservative starting strength
- 0.1 percent = 1 mg/mL, most common serum strength
- 0.2 percent = 2 mg/mL, top of the published cosmetic range
- Apply once or twice daily, typically at night
- Expect a visible blue tint on the skin that fades in a few minutes
Injectable GHK-Cu Dosing
Self-directed subcutaneous protocols typically run 1 to 2 mg once daily, with 2 mg the most commonly reported figure, for roughly 30 days. The upper anecdotal range is about 3 mg daily. It is important to be direct about the evidence here: no human trial has established a safe or effective injectable GHK-Cu dose. These numbers come from community practice and extrapolation from in vitro concentrations, not from a protocol anyone published.
The practical consequence is that the conservative end of the range is the reasonable place to sit. There is no data showing 3 mg outperforms 1 mg, and the copper load scales linearly with the dose.
- Days 1 to 7: 1 mg once daily to establish tolerance, since injection site stinging is the most common complaint.
- Days 8 to 30: 2 mg once daily if the first week was uneventful, rotating injection sites.
- After day 30: stop injectable use for a full 4 weeks.
- Before any second cycle: check serum copper and ceruloplasmin.
Reconstitution and Syringe Math
For injectable use, a 50 mg vial with 5 mL of bacteriostatic water gives 10 mg/mL, which keeps the injection volume small and the math clean. At that concentration a 1 mg dose is 0.1 mL, which is 10 units on a U-100 insulin syringe, and 2 mg is 0.2 mL, which is 20 units.
- 50 mg vial + 5 mL BAC water = 10 mg/mL (1 mg = 10 units, 2 mg = 20 units)
- 50 mg vial + 10 mL BAC water = 5 mg/mL (1 mg = 20 units, 2 mg = 40 units)
- 20 mg vial + 2 mL BAC water = 10 mg/mL (1 mg = 10 units, 2 mg = 20 units)
- 100 mg vial + 10 mL BAC water = 10 mg/mL (2 mg = 20 units)
If your vial size is not on that list, enter it into the GHK-Cu calculator, which is preloaded with a 50 mg vial and a 2 mg dose, or the general peptide calculator for a fully custom concentration. Both show the exact unit mark to draw to on a live syringe diagram.
Add bacteriostatic water slowly down the inner wall of the vial rather than directly into the powder, then swirl gently. A correctly reconstituted solution is a clear, deep blue. That color is the copper complex and is expected, not a sign of contamination. A colorless solution suggests the product is not actually copper-complexed. Discard anything cloudy, particulate, or shifting toward brown.
Why Copper Caps the Cycle Length
The peptide portion of GHK-Cu clears quickly. The copper does not. Each 2 mg dose delivers copper that the body eliminates more slowly than it eliminates the tripeptide, so daily injectable dosing accumulates in a way that daily topical use largely does not. This is the reason the standard practice is a 30-day run followed by a 4-week break, rather than continuous use.
Practical markers to check before a repeat cycle are serum copper and ceruloplasmin, both of which are inexpensive and widely available. Anyone with Wilson disease or another copper handling disorder should avoid GHK-Cu entirely, by any route, since the entire point of the molecule is copper delivery.
Injection Sites and Common Side Effects
Subcutaneous GHK-Cu is injected into abdominal fat, the outer thigh, or the back of the arm using a 29 to 31 gauge insulin syringe. Site rotation matters more here than with most peptides: the copper complex is locally irritating and can leave a temporary blue-green mark at the site that resolves over a day or two.
- Stinging or burning during injection, the most frequently reported effect
- Temporary blue or green discoloration at the injection site
- Localized redness or a small welt that fades within 24 hours
- Nausea or a metallic taste at higher doses, which typically signals backing off
For site selection, needle depth, and rotation patterns, see the peptide injection sites guide. For structuring the 30-day-on, 4-week-off pattern alongside other compounds, see the peptide cycling guide.
GHK-Cu Compared to Other Repair Peptides
GHK-Cu is often grouped with BPC-157 and TB-500 because all three are discussed in a tissue repair context, but the mechanisms are unrelated. BPC-157 and TB-500 act through angiogenic and cytoskeletal pathways and need no metal cofactor. GHK-Cu is a copper carrier that signals to fibroblasts and drives extracellular matrix output: collagen, elastin, and glycosaminoglycans. Its strongest domain is skin and cosmetic outcomes rather than tendon or gut.
That difference also drives the dosing structure. BPC-157 and TB-500 are typically run in mcg to low mg amounts on multi-week schedules without a heavy metal to track. GHK-Cu carries a cumulative mineral load, which is why its protocol has a hard stop built in.
Storage After Reconstitution
Keep lyophilized GHK-Cu cool, dark, and dry, where it is stable for months to years. Once reconstituted with bacteriostatic water, store at 2 to 8 degrees Celsius, protect it from light, and use within 28 days. Avoid repeated freeze-thaw cycles. Because the blue color is diagnostic for this compound specifically, a solution that loses its color is a reason to discard it even if it otherwise looks clear.