Evidence review: Open Peptide Project (verified against primary PubMed, ClinicalTrials.gov & FDA records) · Last checked 2026-10-27. ← Back to Evidence Library

How to read a peptide certificate of analysis (COA)

Name: How to read a peptide certificate of analysis (COA)
Published: 2026-10-27

What a COA can and cannot tell you, and the gaps independent testing has found

Evidence verdict: A COA is a seller-supplied document, not proof. Published testing shows labels and purity claims on unregulated peptide products are often wrong.

Last reviewed: Oct 27, 2026

In 30 seconds

A COA reports tests someone says they ran on one batch. It is only as good as the lab, the method and the link to the vial in your hand.
HPLC "purity" is not the same as peptide content. Salts, water and fillers can make up much of the powder weight. [Lab]
Test purchases of online semaglutide found 7.7% to 14.37% purity against a 99% label claim, and endotoxin in every sample. [Observational]
FDA-approved peptide drugs are released against validated specifications that FDA reviews. Research-use-only products are not. [Regulatory]

What a COA usually contains

Typical fields are identity (often mass spectrometry), purity (often reversed-phase HPLC with UV detection), appearance, and sometimes water content, counter-ion content, endotoxin and sterility. A missing field means the test was not reported, not that the result was good.

Purity versus content

HPLC with UV detection measures the share of UV-absorbing material that elutes as the main peak. It can miss things that do not absorb UV. In one analysis, quantitative NMR found undeclared mannitol making up 20% and 43% by weight of two commercially sourced custom peptides, which routine LC methods had not flagged (PMID 31671336). [Lab] Counter-ions such as trifluoroacetate, acetate and chloride also add weight and need their own methods, such as ion chromatography (PMID 22252914). [Lab]

Questions to ask of any COA

Does the batch or lot number match the container? Is the testing lab named and accredited, and can the document be checked with that lab? Are the methods and reference standards stated? Does it report endotoxin and sterility if the product is meant to be injected? Is the date recent relative to the product? A COA that answers none of these is a marketing document. This page does not name or rate testing labs.

What independent testing found

A 2024 market-surveillance study bought semaglutide from illegal online pharmacies. All delivered vials were judged probable substandard or falsified; measured purity was 7.7% to 14.37% versus a 99% label claim; no viable microbes grew, but endotoxin was detected in every sample; and none of the ordered pens arrived (PMID 39509151). [Observational] A JAMA analysis of 44 products sold online as SARMs found the label amount matched in only 41% (PMID 29183075). [Observational]

How regulated products differ

For FDA-approved synthetic peptides, FDA guidance asks generic makers to identify and limit peptide-related impurities against the reference drug, because new impurities can carry immunogenicity risk (FDA docket FDA-2017-D-5767; PMIDs 37467878, 41445733). [Regulatory] Nothing comparable applies to products labeled for research use only.

Evidence levels used on this page

[Regulatory] FDA, USP or WADA primary document. [Controlled study] randomized trial or systematic review of trials. [Observational] market surveillance, pharmacovigilance or cohort data. [Lab] cell, analytical or animal work. [Case] single case report.

Counterfeit and mislabeled gray-market peptides, Endotoxins and TFA salts

References

Ashraf AR, et al. Multifactor quality and safety analysis of semaglutide products sold by online sellers without a prescription. J Med Internet Res. 2024. PMID 39509151.
Choules MP, et al. NMR reveals an undeclared constituent in custom synthetic peptides. J Pharm Biomed Anal. 2020. PMID 31671336.
Mrozik W, et al. Determination of counter-ions in synthetic peptides by ion chromatography, capillary isotachophoresis and capillary electrophoresis. J Pept Sci. 2012. PMID 22252914.
Van Wagoner RM, et al. Chemical composition and labeling of substances marketed as selective androgen receptor modulators and sold via the internet. JAMA. 2017. PMID 29183075.
De Groot AS, et al. Immunogenicity risk assessment of synthetic peptide drugs and their impurities. Drug Discov Today. 2023. PMID 37467878.
Mattei et al. Immunogenicity risk assessment of peptide-related impurities identified in generic teriparatide products. Front Immunol. 2025. PMID 41445733.
US FDA guidance. ANDAs for certain highly purified synthetic peptide drug products that refer to listed drugs of rDNA origin (docket FDA-2017-D-5767), as described in PMIDs 41445733 and 39185315.

Disclaimer: This page is for education only. It is not medical advice, and it does not endorse using, buying or preparing any unapproved product. Talk to a licensed clinician before you start, stop or change any treatment.