Most certificates of analysis for research peptides look alike. There's a purity percentage from HPLC near the top, a mass from mass spectrometry somewhere below it, and a lab logo if you're lucky. For a simple single peptide, reading one is quick.
Two products in our catalog are harder to read, though. One is retatrutide, a large modified peptide. The other is the BPC-157 and TB-500 blend, which puts two different peptides in one vial. Each one can produce a COA that looks fine at a glance and still doesn't prove much. Here's what to look for on each.
Retatrutide: a big molecule with a confusing spectrum
Retatrutide is an investigational compound from Eli Lilly. It acts on three receptors (GIP, GLP-1 and glucagon), it is still in Phase 3 trials, and it has no FDA approval, according to Drugs.com. Anything sold today under that name is research material.
What makes the COA tricky is the molecule itself. KEGG, the Kyoto drug database, lists retatrutide as a modified peptide with the formula C221H342N46O68 and a molecular weight of 4731.34. Its sequence includes non-standard residues, so you can't work out the expected mass by adding up amino acids from a chart the way you can for simpler peptides. You need the published formula, and the COA should be checked against it.
Then there's the part that's easy to misread. Mass spectrometers that use electrospray ionization add protons to a molecule, and a molecule this size usually picks up several. The instrument reads mass divided by charge, so retatrutide may never show a peak anywhere near 4,731. Working from KEGG's exact mass, the triply charged ion lands at about 1577.2 and the quadruply charged ion at about 1183.1. A COA showing peaks near those numbers can be a perfectly good result. A COA that just prints "4731" with no spectrum and no explanation tells you less than it seems to.
So for retatrutide, we'd check four things:
- The identity is stated properly. A listing should give the molecular formula or the CAS number, which KEGG gives as 2381089-83-2.
- The COA says which mass it reports, average molecular weight or the observed charged ions, and the numbers fit one of the values above.
- The HPLC purity comes with the actual chromatogram, not just a percentage.
- The lab is named, and the lot number on the COA matches the vial.
Our retatrutide peptide page lists the CAS number above, and we'd encourage anyone to hold it to the same four checks they'd use on any other supplier.
The BPC-157 + TB-500 blend: two peptides, two answers
Blends have a different problem. Each peptide on its own is fairly easy to verify. Put them in one vial and a lazy COA can blur them together.
BPC-157 is a 15-residue peptide with the sequence GEPPPGKPADDAGLV and the formula C62H98N16O22. That works out to a molar mass of 1419.556 g/mol, according to its Wikipedia entry. TB-500 is much smaller. BSCG, the sport testing group, describes it as a synthetic fragment of thymosin beta-4 covering residues 17 to 23, acetylated at the front end (Ac-LKKTETQ). Our own calculation puts that at about 889 g/mol as a free acid, or about 888 if the far end is an amide. That one dalton gap matters more than it looks, because a report rounded to whole numbers can make either version look right.
For a vial like our BPC-157 + TB-500 (Wolverine Blend), a useful COA should show:
- Two identities. The mass spec should find a match for BPC-157 near 1419.6 and a separate match for TB-500 near 889 or 888, depending on which terminus was made.
- Two quantities. Each peptide should be measured separately. A single purity number for the whole vial says nothing about the ratio between them.
- Which TB-500 form it is. If the COA doesn't say free acid or amide, ask. It changes the number you're checking against.
- The basics still apply: a named lab, a matching lot number and a test date.
If a blend COA shows one peak, one percentage and nothing else, we'd treat it as incomplete, however high the number is.
A word on the regulatory noise
Both peptides in the blend were in the news this summer. On July 23, 2026, the FDA's Pharmacy Compounding Advisory Committee voted 8 to 6, with one abstention, to recommend BPC-157 and TB-500 for compounding, according to PharmExec. The vote is non-binding, the FDA is not bound by it, and the evidence base is still thin. ABC News noted that most BPC-157 studies so far have been in rodents.
None of that changes how a COA should look. If anything, more attention on these compounds means more listings, and more listings means more certificates worth reading carefully.
The short version
For retatrutide, check the identity against the published formula and expect to see charged ions rather than the full molecular weight. For the blend, insist on two identities and two quantities. For both, a named lab and a matching lot number come first. A supplier that can't provide those isn't really giving you a COA.
All GMR Peptides products are sold for laboratory research only and are not for human or veterinary use.
Top comments (0)