How to Judge Quality Claims from Peptide Sellers

The short answer

No online seller of "research peptides" sells a medicine. Products labelled for research use or "not for human consumption" are not approved drugs and are not made under the controls that approved drugs are, and FDA has warned companies that sold unapproved semaglutide, tirzepatide, retatrutide, survodutide and mazdutide falsely labelled that way.¹ For an approved drug, FDA's advice is to buy only from a state-licensed pharmacy.¹

For anything else, paperwork is the only evidence a buyer has, and paperwork can be wrong. When researchers test-bought semaglutide vials from illegal online pharmacies, the labels claimed 99% purity; the measured purity was 7.7% to 14.4%, the semaglutide content was 29% to 39% above the labelled amount, and every vial contained bacterial endotoxin. The three prefilled pens they ordered never arrived.² This guide explains what a quality claim has to show before it means anything, and where even good documents stop.

What researchers found when they bought online

The most detailed look at this market is a 2024 study of semaglutide sold online without a prescription. Of 1,080 search-engine links the researchers collected, 317 led to online pharmacies, and 134 of those, 42%, led to 59 illegal pharmacy websites; the top 30 domains linked to illegal pharmacies drew more than 4.7 million visits in three months of 2023. The team placed test orders with the six illegal pharmacies offering semaglutide most widely at the lowest prices. The three prefilled Ozempic pens never arrived, which the authors classed as non-delivery scams, and the three vials that did arrive failed more than half of the visual inspection criteria before any laboratory test was run.²

In the laboratory the vials held more semaglutide than labelled, contained no peptide-like impurities and grew no microorganisms, yet measured only 7.7% to 14.4% pure against the 99% printed on their labels, and all carried endotoxin at 2.2 to 9.0 endotoxin units per milligram.² A product can pass one test and fail another, which is why a single number on a label proves little.

What a certificate of analysis has to show

A certificate of analysis (COA) is a laboratory's report on one batch. Our COA decoder walks through a real one line by line; these are the parts that carry the weight.

Identity, by mass spectrometry. The measured molecular mass should match the peptide's expected mass. Purity testing alone cannot tell you the peak is the right molecule.

Purity, by HPLC. High-performance liquid chromatography reports the main peak as a percentage of what the detector sees. That qualifier matters: the usual UV detection cannot see compounds that absorb no UV light. In one analysis of two commercially made research peptides, nuclear magnetic resonance found that 20% and 43% of the material by weight was mannitol, a sugar alcohol nobody had declared, which UV-based chromatography would have missed.³

Quantity. Purity is not the same as how much peptide is in the vial. The online semaglutide vials above held more than their labelled amount of semaglutide yet measured far below their labelled purity, so a single "99%" figure answered neither question.²

Endotoxin and sterility, for anything injected. Endotoxins are fragments of bacterial cell walls that cause fever and inflammation even when no live bacteria remain. The pharmacopoeial methods are the bacterial endotoxins test and the sterility test in the United States Pharmacopeia.^{4 5} The semaglutide vials were free of live microorganisms and still carried endotoxin.²

A named, accredited laboratory, a batch number and a date. The laboratory's competence standard is ISO/IEC 17025.⁶ The batch number on the report should match the vial, because a report for one batch says nothing about another.

Warning signs in a quality claim

Each of these means the claim cannot be checked, which is not the same as proof the product is bad:

• A purity figure with no chromatogram, no laboratory name and no batch number.
• The same certificate shown for every batch, or a certificate dated long before the batch was made.
• Identity asserted without a mass-spectrometry result.
• An injectable product with no endotoxin or sterility result.
• A "research use only" label on a product sold with human doses, reviews of personal use or injection instructions. FDA describes such labels as false when the product is marketed for people.¹

Testing the vial in your hand

The only way to know what is in a particular vial is to test that vial. Our verification guide explains how independent testing works, what each test can detect and how to read the result. Two limits apply to every result: a test measures only what it looks for, which is why the mannitol above went unnoticed until someone used a different method,³ and one vial describes one vial, not the batch or the next order.

What this cannot do

Good documents lower some risks; they do not make an unapproved compound safe or effective. Identity, purity and sterility say nothing about whether a peptide works in people or what its side effects are, and for most research peptides those questions have not been answered by trials. Our encyclopedia entries report what each compound's human evidence shows, and our regulatory tracker follows FDA's decisions on which peptides pharmacies may compound. Where an approved medicine exists for a condition, it comes with manufacturing controls, a label and a pharmacist, none of which a research-peptide seller provides.

Frequently asked questions

Can a certificate of analysis prove a peptide is safe?

No. At best it shows what one laboratory found in one batch: identity, purity, and for injectables endotoxin and sterility. It says nothing about whether the compound is safe or effective in people, and a certificate can be wrong or copied.

What does HPLC purity actually measure?

The main peak as a percentage of what the detector sees. With the usual UV detection, compounds that absorb no UV light are invisible; one study found 20% and 43% undeclared mannitol in two commercial research peptides that way.

Is "for research use only" legal?

The label does not make a product legal to sell for people. FDA has warned companies that sold unapproved GLP-1 drugs falsely labelled for research purposes or not for human consumption.

Does a higher price mean better quality?

We know of no study that links price to quality in this market. The evidence that matters is a batch-specific test result from a named laboratory, or an independent test of the vial itself.

Related on Grey Peptides

• How to verify a peptide
• COA decoder
• Peptide side effects
• Regulatory tracker

Sources

1. U.S. Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss: warnings to companies selling semaglutide, tirzepatide, retatrutide, survodutide or mazdutide falsely labelled "for research purposes" or "not for human consumption"; buy only from state-licensed pharmacies. Content current as of September 1, 2026; read September 30, 2026. FDA
2. Ashraf, A. R. et al. (2024). Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription: Market Surveillance, Content Analysis, and Product Purchase Evaluation Study. J Med Internet Res, 26, e65440. PMID: 39509151 · doi:10.2196/65440
3. Choules, M. P. et al. (2020). NMR reveals an undeclared constituent in custom synthetic peptides. J Pharm Biomed Anal, 178, 112915. PMID: 31671336 · doi:10.1016/j.jpba.2019.112915
4. United States Pharmacopeia. General Chapter <85> Bacterial Endotoxins Test.
5. United States Pharmacopeia. General Chapter <71> Sterility Tests.
6. International Organization for Standardization. ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories.

This guide explains how to read quality claims. It is not an endorsement of buying unapproved compounds, and it is not medical advice; approved medicines should come from a licensed pharmacy.