Contents
Key findings
- 1A typical vendor CoA reports HPLC purity and a mass-spectrometry identity check for a batch of raw material. It says nothing about the amount in your vial, sterility, endotoxin, heavy metals, or whether the document even matches the product.
- 2"99% purity" by HPLC means 99% of what absorbed UV at one wavelength was the main peak — not that the vial contains 99% of the labelled dose, and not that the remaining 1% is harmless.
- 3Peptide impurities are not random: truncated, deleted and oxidised sequences from synthesis can be biologically active or immunogenic and are hard to see on a single-method CoA.
- 4Independent testing of grey-market and compounded peptides has repeatedly found under-dosing, mislabelling and, for GLP-1 products, counterfeits; the FDA has issued warnings and seizures.
- 5The only reliable fix is a pharmaceutical quality system — GMP manufacture, validated methods, batch release, and regulatory oversight — which "research use only" products by definition lack.
Evidence level
The analytical principles described (HPLC purity, mass-spec identity, quantity, sterility and endotoxin testing) are standard pharmaceutical quality science. Findings about grey-market products come from published independent testing and regulatory reports and are cited.
Regulatory status
"Research use only" peptides are unapproved products manufactured outside pharmaceutical quality systems. The FDA has reported adverse events and identified counterfeit and mislabelled GLP-1 products, and has cited peptide-impurity and characterisation problems in its compounding reviews.
Every "research peptide" vendor offers the same reassurance: a certificate of analysis showing "99%+ purity". It looks scientific because it is — an HPLC trace and a mass spectrum are real measurements. The problem is what they measure, what they don't, and the gap between a document about a batch and the contents of the vial in your hand.
The question readers ask
Does a CoA prove a peptide is safe and correctly dosed? No. At best it shows that a sample of raw material contained mostly the intended molecule at the moment it was tested. It does not establish dose, sterility, endotoxin, heavy metals, degradation, or that the sample and your product are the same thing.
What a typical vendor CoA contains
Most CoAs shown online report two things:
- HPLC purity. The peptide is run through a chromatography column and detected by UV absorbance, typically at 214–220 nm. The area of the main peak divided by the total area of all peaks is reported as "purity" — 98.7%, 99.2%, and so on.
- Mass spectrometry identity. The measured molecular mass matches the expected mass of the target sequence, confirming that the main component is (probably) the right molecule.
Some add appearance ("white lyophilised powder") and sometimes a water-content figure. That is usually all.
What "99% pure" actually means — and doesn't
It is a ratio of peaks, not a statement about your dose. A vial labelled 5 mg that is "99% pure" could contain 5 mg, 3 mg or 8 mg of peptide. Purity says nothing about quantity. Peptide content depends on how much powder was actually dispensed and how much of that powder is peptide rather than counter-ions and water — figures the CoA rarely reports.
The remaining 1% is not random dirt. Peptides are built one amino acid at a time. Every step can fail slightly, producing sequences with a missing residue (deletion), a stopped chain (truncation), an oxidised methionine or tryptophan, a racemised residue, or leftover protecting groups. These impurities are close relatives of the intended molecule; some are biologically active in their own right and some are potentially immunogenic. In its guidance for synthetic peptide drugs, the FDA expects manufacturers to characterise any peptide-related impurity above 0.1% and to assess its immunogenicity risk[5]. A single "99%" figure from one UV wavelength does none of that.
One method sees what one method sees. Impurities that don't absorb at the chosen wavelength, co-elute with the main peak, or aren't peptides at all (solvents, metals, endotoxin) are invisible on that chromatogram.
What a CoA almost never tells you
- Sterility. Peptides sold for "research" are typically lyophilised powder in a vial that was not filled aseptically. Injection of non-sterile material risks infection.
- Endotoxin. Bacterial endotoxin (lipopolysaccharide) is a fever-inducing contaminant that survives filtration and sterilisation and must be tested for in every injectable — by the LAL/rFC test to pharmacopoeial limits[4]. It is essentially never on a vendor CoA.
- Elemental impurities. Heavy metals from synthesis reagents and equipment.
- Degradation. Peptides oxidise, deamidate and aggregate with time, heat and light. A CoA describes the batch when tested, not the vial after shipping and storage.
- Chain of custody. The most basic question: is the CoA for this product? PDFs are trivially reused, altered or generated. Batch numbers on the document may or may not match the vial, and matching a number proves little.
What independent testing has found
When researchers, journalists and regulators have tested grey-market and compounded peptides, the pattern is consistent enough to be predictable: a meaningful share of products are under-dosed, some contain a different peptide or none, purity often falls short of the CoA, and sterility and endotoxin are rarely assured. For GLP-1 drugs specifically, the FDA has documented adverse events with compounded products (including overdoses from vial-and-syringe dosing errors), seized counterfeit pens containing wrong or unknown contents, and warned patients accordingly[1].
The same regulator, reviewing peptides nominated for compounding, placed BPC-157, CJC-1295, ipamorelin acetate and others in category 2 in September 2023 — substances judged to present significant safety risks — explicitly citing possible immunogenicity and "complexities with regard to peptide-related impurities and active pharmaceutical ingredient (API) characterization"[2]. In other words, the impurity problem described in this article is the regulator's own stated concern, not a hypothetical one.
Reading a CoA critically
If you are looking at one anyway, ask:
| Question | What a good answer looks like | What you usually get |
|---|---|---|
| Who ran the test? | Named, accredited third-party lab with a verifiable report | Vendor's own lab or an unnamed contractor |
| What was tested? | The finished, filled product from this lot | Bulk raw material, lot unclear |
| Purity by what method? | HPLC at ≥2 wavelengths plus MS; impurities individually reported | One HPLC trace, one number |
| How much peptide is in the vial? | Assay/content vs. label with acceptance range | Not stated |
| Sterile? Endotoxin? | Sterility test and endotoxin result within limits | Not stated |
| Metals, solvents, water? | Reported with limits | Not stated |
| Can I verify it? | Report retrievable from the lab by lot number | PDF on the vendor's site |
The honest conclusion
A CoA is a partial answer to one question (is the main component the right molecule?) and no answer to the questions that determine whether an injected product is safe (how much, how clean, how sterile, and is it really this batch). That is not a criticism of chromatography; it is a description of what a quality system exists to do and a PDF cannot. Products sold "for research use only" sit outside that system by design.
Where to go next
- Peptide safety hub — what is and isn't known about each peptide's safety.
- FDA-approved, off-label, investigational and unapproved peptides.
- GLP-1 peptides: established uses versus emerging research — the compounded and counterfeit product story.
Frequently asked questions
- What does a certificate of analysis actually show?
- Usually an HPLC purity percentage and a mass-spec identity confirmation for a batch of raw peptide. It does not show the amount in your vial, sterility, endotoxin, heavy metals, or that the document matches the product you received.
- Is 99% purity good?
- It is a statement about the main peak on a chromatogram, not about dose or safety. The FDA expects individual peptide impurities above 0.1% to be characterised for immunogenicity in approved products; a single "99%" number does none of that.
- Can I trust third-party testing?
- Independent testing is better than a vendor PDF, but a single sample tested once tells you about that vial, not the next batch. Only a quality system with batch release covers the product you actually buy.
References
Numbered in order of first use. Study type is shown for every source; see our methodology for how we rank evidence.
- 1.
FDA's concerns with unapproved GLP-1 drugs used for weight loss U.S. Food and Drug Administration, 2025.
Regulatory source
Result: Adverse events with compounded products, dosing errors, and counterfeit pens; enforcement actions.
↑ back to text - 2.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (category 2 list) U.S. Food and Drug Administration, 2026.
Regulatory source
Result: Ipamorelin acetate and kisspeptin-10 remain in category 2; BPC-157, CJC-1295, TB-500 and injectable GHK-Cu appear on the withdrawn-nomination list.
↑ back to text - 3.
Current Good Manufacturing Practice (CGMP) Regulations U.S. Food and Drug Administration.
Regulatory source
Result: Describes the quality-system requirements (identity, strength, quality, purity) that approved drugs must meet.
↑ back to text - 4.
USP General Chapter <85> Bacterial Endotoxins Test United States Pharmacopeia.
Guideline
Result: Standard method and limits for endotoxin in injectable products.
↑ back to text - 5.
ANDAs for Certain Highly Purified Synthetic Peptide Drug Products That Refer to Listed Drugs of rDNA Origin U.S. Food and Drug Administration, 2021.
Regulatory source
Result: FDA's expectations for characterising peptide-related impurities (including immunogenicity risk of impurities above 0.1%).
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Review status: Editorially reviewed against primary sources. This article was fact-checked against the primary sources listed in the references by our editorial team, and it has not been reviewed by a licensed clinician. It is educational content, not medical advice. Read our editorial policy and methodology. Spotted an error? Tell us.
