@selfcarerebuild's GHK-Cu peptide mixing claims, fact-checked

What did @selfcarerebuild actually say?

The creator made two distinct claims: first, that copper in GHK-Cu will "degrade other peptides" when they share a vial or are injected together, and second, that GHK-Cu's molecular size "will actually disrupt your absorption of your other peptides" when co-injected. The practical advice that followed was to separate GHK-Cu from other peptides by at least 30 minutes, or split into morning and evening doses. This is the kind of advice that sounds chemistry-adjacent enough to seem credible, which is exactly why it deserves a closer look.

To be fair, the creator is touching on a real biochemical tension. GHK-Cu is a copper-chelating tripeptide, and copper ions are known to participate in oxidative reactions. That part is not invented. The question is whether the leap from "copper exists" to "your other peptides are ruined" is supported by any actual evidence.

Does the science back this up?

Partially, and that partial is doing a lot of work here. The copper degradation claim has a real, if overstated, basis. Copper ions can catalyze oxidative degradation of certain amino acid residues, particularly methionine and cysteine, through reactive oxygen species. This is documented in pharmaceutical stability literature (Stadtman, 1993, Biochemistry). However, GHK-Cu does not freely release ionic copper the way the creator implies. The copper in GHK-Cu is chelated, meaning it is bound within the peptide structure, which substantially limits its reactivity compared to free ionic copper.

On the molecular size and absorption claim, the evidence is much weaker. GHK-Cu has a molecular weight of roughly 340 daltons, which is small by peptide standards. BPC-157 is around 1,419 daltons. The idea that GHK-Cu's size creates a competitive absorption problem at a subcutaneous injection site is not supported by any pharmacokinetic study the fact-check team could locate. Subcutaneous injection does not work like a molecular size filter.

What did they get wrong (or right)?

They got the general instability concern directionally right but then dramatically overstated it. Copper-mediated oxidation of co-formulated peptides is a real concern in pharmaceutical compounding, particularly for peptides containing susceptible residues. Some compounding pharmacies do separate GHK-Cu from other peptides for this reason. That is legitimate practice rooted in reasonable caution.

What they got wrong is the mechanism and the certainty. Saying copper "will degrade" your other peptides treats a potential stability risk as a guaranteed outcome, which is not how chemistry works in practice. Stability depends on pH, temperature, concentration, exposure time, and which specific peptides are co-formulated. A study by Vogt et al. (1994, Pharmaceutical Research) showed that copper-mediated peptide oxidation rates vary enormously depending on formulation conditions.

The molecular size absorption claim is simply not supported. Injecting two peptides of different molecular weights into the same subcutaneous site does not create a size-based competition for absorption. This appears to be a confident-sounding extrapolation with no pharmacokinetic basis.

What should you actually know?

If you are using GHK-Cu alongside other peptides, the most honest answer is: the evidence for strict separation is suggestive but not definitive for typical research or therapeutic contexts. Here is what the science actually supports.

• Chelated copper in GHK-Cu has lower free-radical reactivity than ionic copper, but the stability of co-formulated peptides over weeks in a vial is a legitimate concern worth discussing with a compounding pharmacist.
• Peptides containing methionine or cysteine residues (like some growth hormone secretagogues) may be more vulnerable to oxidative degradation than others.
• Separating GHK-Cu into its own vial is a reasonable precaution, not a proven necessity. Calling it a certainty overstates what we know.
• The absorption competition claim based on molecular size has no peer-reviewed support for subcutaneous administration. Ignore that part.
• None of this should be interpreted as a recommendation to self-administer any peptide. Peptide therapy should involve a licensed provider who can assess your specific formulations and health context.

The creator is clearly enthusiastic and trying to be helpful. But confident delivery is not the same as correct information, and in a space where people are making decisions about compounds they are injecting, the distinction matters.