Peptide quality: how to read a certificate of analysis

Why quality matters

Peptides are fragile, hard to purify, and often sold outside regulated supply chains. FDA's safety reviews of compounding peptides repeatedly cite peptide-related impurities, aggregation, and difficulty characterizing the active ingredient as reasons for concern, because these can trigger immune reactions ². In regulated compounding, a bulk ingredient must come from an FDA-registered manufacturer with a valid certificate of analysis ¹; gray-market products have no such requirement.

How to read a Certificate of Analysis (COA)

A COA is a document reporting test results for a specific manufacturing lot. Useful things to look for:

Identity (mass spectrometry, MS): confirms the molecule's mass matches the expected sequence. Without identity testing, purity numbers are meaningless, because a sample can be "99% pure" of the wrong compound.
Purity (HPLC): high-performance liquid chromatography separates the main peptide from related impurities (truncated sequences, deletion sequences, oxidized forms). Purity is reported as the main peak's share of total peak area at a given wavelength. It does not tell you how much peptide is in the vial.
Net peptide content: the percentage of the powder's weight that is actually peptide, as opposed to water, counter-ions and salts. Lyophilized peptides commonly contain a meaningful fraction of non-peptide mass, so a vial with 99% HPLC purity may have considerably less than the labeled peptide weight.
Counter-ion (TFA vs. acetate): peptides cleaved and purified with trifluoroacetic acid are often supplied as TFA salts. Pharmaceutical products usually exchange this for acetate or another counter-ion, since residual TFA is undesirable for biological use.
Endotoxin (LAL or recombinant Factor C test): measures bacterial endotoxin, reported in EU/mg. Endotoxin can cause fever and inflammatory reactions and is not removed by filtering out live bacteria.
Sterility: required for any injectable pharmaceutical; a sterility test checks for viable microorganisms.
Residual solvents and heavy metals: tested in pharmaceutical-grade material.
Lot number, test date, lab name and method: a COA should match the lot on the vial and identify who performed the testing.

A COA with no lot number, no lab identification, identical results across many products, or only an HPLC chromatogram (no MS) offers little assurance.

Independent (third-party) testing

Independent testing means a lab with no financial tie to the seller analyzes a sample, ideally one purchased anonymously. Look for accredited labs (for example ISO/IEC 17025) and reports that can be verified directly with the lab. Even good third-party results apply only to the lot tested and say nothing about sterility of other vials or about whether a substance is safe or effective in people.

What studies of gray-market products have found

Semaglutide sold online (2024): researchers test-purchased products from six online sellers. None of the three branded Ozempic pens arrived (non-delivery scams), and none of the six sellers asked for a prescription. The three "research" semaglutide vials that did arrive showed purity of only about 8-14% against a claimed 99%, semaglutide content 29-39% higher than labeled, and detectable endotoxin in all three ³.
Australian anti-doping lab (Sport Integrity Australia): of more than 200 suspected peptide products (bought online or seized at the border), only about a quarter contained the labeled peptide; about a quarter contained no peptide at all, and one "growth hormone" product contained porcine insulin, which can cause dangerous low blood sugar ⁴.
German Sport University Cologne (2017): black-market products included altered peptides, such as GHRP-6 and growth hormone with extra amino acids attached, and 44% of doping-relevant ingredients across products were undeclared or falsely declared ⁵.
Contamination outbreaks: in August-September 2026, FDA and CDC reported more than two dozen illnesses in at least four states linked to compounded glutathione (a tripeptide) injections contaminated with endotoxins ⁸.

Red flags

"Research use only" labels combined with health claims, dosing calculators, or bundled bacteriostatic water and syringes; FDA cites exactly these as evidence of human drug intent ⁶⁷.
Investigational drugs still in clinical trials (for example retatrutide, survodutide, mazdutide) offered for sale ⁷.
No lot-specific COA, or COAs that cannot be verified with the testing lab.
Purity claims without identity (MS) or endotoxin data.
Prices far below legitimate pharmacy prices, payment only by crypto or peer-to-peer apps, or no physical business address.
Brand-name products sold without a prescription ³.

Peptide Quality: Certificates of Analysis, Testing, and Red Flags