Red flags in a peptide COA: spotting a fake

What does a red flag on a peptide COA mean?

A red flag on a certificate of analysis is a question, not a verdict: it means the document cannot be taken at face value until someone checks it. A certificate of analysis (COA) is a claim about one batch, made by a named laboratory, on a stated date. FDA's guidance on manufacturing practice for drug ingredients sets out what an authentic certificate carries: the batch number, the date, each test performed with its acceptance limit and the numerical value obtained, and, where a certificate is reissued by an agent or broker, the name of the laboratory that actually performed the analysis. Research peptides are not held to that guidance, but it is a fair yardstick for what a complete document looks like.

If you are new to reading one, start with How to read a peptide certificate of analysis. This page is about what should make you stop. None of the signs below proves a certificate is fake. Genuine certificates contain errors, and we have found several in our own, which we use as examples throughout. What a red flag tells you is that the document cannot be taken at face value until someone checks it.

What lot and laboratory problems should I look for on a COA?

Look for a missing or mismatched lot number, one certificate reused across lots, a certificate on the wrong product, a laboratory you can't find, and identical layouts naming different laboratories.

No lot number, or a lot that doesn't match the vial. A certificate without a lot number describes nothing in particular. One whose lot differs from the label on the vial you received describes a different batch. Ask the supplier which certificate covers your lot; if the answer is that one certificate covers everything, that is the next flag.

One certificate reused across lots, or a "representative" certificate. Purity is measured on a sample from one batch, and the next batch is a new measurement. A certificate offered as representative of a product, rather than of a lot, is a description of what the supplier hopes is typical.

A certificate on the wrong product. This happens by accident as well as by design, and we have done it ourselves: when a product page address was corrected, the certificate lookup was not moved with it, and our AOD-9604 page briefly showed Tesamorelin's certificate, with its lot, purity and formula. The compound name and formula on a certificate should match the product it is shown beside. That page now shows no certificate, because the supplier publishes none for AOD-9604.

No laboratory named, or one you can't find. A certificate should name the laboratory that ran the analysis, not only the brand that ordered it. Search for the laboratory independently, not through a link on the certificate, and check that it exists, does this kind of work, and can be contacted.

Identical layouts naming different laboratories. Laboratories use their own templates. When several certificates share one letterhead and layout but name different laboratories, the documents were probably prepared by someone other than the laboratories. That can be legitimate, as when a supplier collects a lab's findings into its own format, but it is not the same as a certificate issued by the lab. Nine of our certificates came from one supplier's library in exactly this form: one layout, four laboratories. We labelled them as supplier-provided until the laboratories named on them confirmed them.

What purity and chromatogram problems should I look for?

Be wary of a round minimum instead of a measured purity, and of a chromatogram that is missing, cropped, or doesn't fit the stated purity.

A round minimum instead of a measured value. "Purity ≥99%" is a specification, not a measurement. A lot that was actually analysed has a figure, such as 99.59% for our BPC-157 lot. Some laboratories report a lower bound when the measured value is above what they will state: our Selank certificate reads >99.80%. That is still a reported figure for one lot, which a catalogue-wide "≥99%" is not. For what a point of purity does and doesn't mean, see Peptide purity: 98% vs 99% in practice.

A chromatogram that is missing, cropped, or doesn't fit the stated purity. The HPLC chromatogram is the raw evidence behind a purity figure: the main peak's share of the total peak area. A certificate without one asks you to take the number on trust. One cropped tightly around the main peak hides the region where impurities would appear. Those smaller peaks matter: in synthetic peptides they are typically related impurities, such as sequences missing or carrying an extra amino acid, oxidised forms and leftover protecting groups, as a review of peptide impurities sets out. And if the trace shows sizeable peaks beside the main one while the stated purity is above 99%, the two do not agree. Only five of our certificates include a chromatogram, and where a document's own frame clips the axis, we reproduce it as printed rather than tidy it.

How do I check a COA's molecular formula against its weight?

A molecular formula and a molecular weight are two statements about the same molecule, so one can be checked against the other. Add up the atomic weights in the formula and compare the total with the weight printed on the certificate. Then compare the formula with an independent record, such as PubChem, or recompute it from the sequence.

We did this for every certificate we hold, and three printed a formula that did not fit. The Tesamorelin certificate's formula lists 44 nitrogen atoms; tesamorelin has 72, and the printed formula works out to about 4,780 g/mol against the certificate's own 5,135.85. The MOTS-c certificate lists one sulfur atom, but MOTS-c contains two methionines, each carrying a sulfur. The IGF-1 LR3 certificate counts six hydrogen atoms too many, treating its cysteines as free rather than joined in three disulfide bonds, and comes out about 6 g/mol above its own stated 9,111.

In each case the stated molecular weight matched the real compound and the formula was the error, which looks more like a transcription slip than a different substance. We keep the printed formula as the record and show the corrected one beside it with the reason. A mismatch like this is a reason to ask, not to conclude, but a certificate whose formula belongs to a different molecule altogether should not be accepted until it is explained.

What date, identity and verification problems should I look for?

Look for dates that don't add up, purity reported without an identity test, and no way to verify the certificate with the laboratory.

Dates that don't add up. A certificate should be issued after the sample was received, and both should fall before the product reached you. An issue date earlier than the date the sample was received, or a lot code that encodes a date later than the issue date, needs explaining. We caught one of these in our own records: nine certificates read "Date Issued: 6/18/2026", with the sample received on June 16, but we had transcribed the issue date as May 18, a month before the laboratory had the sample. The documents were right and our record was wrong, and we corrected it.

No identity test. Purity tells you how much of the sample is the main compound. It does not tell you the main compound is the one on the label: a different peptide can be just as pure. Identity needs a separate test, usually mass spectrometry or a comparison against a reference standard. Official medicines laboratories screening seized peptide products work the same way, identifying each peptide by LC-MS/MS and only then measuring how much is there by UHPLC. HPLC vs mass spec: what each test proves explains the difference. Several of our certificates report purity without an identity test, including those for Selank, MOTS-c, IGF-1 LR3 and Semax, and our testing page lists what each one reports.

No verification route. The strongest certificate is one you can check with the laboratory rather than only download from the seller. Some laboratories let you look a certificate up by batch number; others need a certificate number and an access code. None of our certificates currently links to a laboratory verification page, which is why we say who supplied each one and which laboratory it names.

What should I do if a COA shows red flags?

Ask the supplier, specifically: which lot this certificate covers, who issued it, and whether the laboratory will confirm it. A supplier that works from real certificates can usually answer all three. Then contact the laboratory yourself, using details you found independently. If the certificate shows several of the flags above and the answers do not resolve them, treat the purity figure as unverified.

Our COA library lists every certificate we hold, with its lot, laboratory, date and any known correction, along with the products that do not have one yet. For the wider checks on a supplier, beyond its paperwork, see How to vet a peptide supplier: a 10-point checklist. All products are for laboratory research use only.

References

1. D'Hondt M, Bracke N, Taevernier L, Gevaert B, Verbeke F, Wynendaele E, De Spiegeleer B (2014). Related impurities in peptide medicines. J Pharm Biomed Anal. [REVIEW] PubMed record for reference 1, D'Hondt 2014
2. Vanhee C, Janvier S, Desmedt B, Moens G, Deconinck E, De Beer JO, Courselle P (2015). Analysis of illegal peptide biopharmaceuticals frequently encountered by controlling agencies. Talanta. [IN VITRO] PubMed record for reference 2, Vanhee 2015

Sources

1. FDA, Q7 Good Manufacturing Practice Guidance for Active Pharmaceutical Ingredients, Guidance for Industry (Revision 1, September 2016), section 11.4, Certificates of Analysis (fda.gov, source 1, accessed October 20, 2026)
2. PubChem, Tesamorelin (CID 16137828): molecular formula C221H366N72O67S (pubchem.ncbi.nlm.nih.gov, source 2, accessed October 20, 2026)
3. PubChem, MOTS-c (CID 146675088): molecular formula C101H152N28O22S2 (pubchem.ncbi.nlm.nih.gov, source 3, accessed October 20, 2026)