How to Read a Certificate of Analysis for Peptides

A certificate of analysis for peptides is a lot-specific lab record, and you read it by matching the lot number to your product, then checking each test result against its stated limit for identity, purity, and potency. For an injectable, also confirm sterility and endotoxin results for the finished preparation, because a high purity figure says nothing about either.

Most guides to this topic are written for people buying research peptides from online vendors. A clinic has a different job: confirming that a licensed pharmacy can document what it is dispensing for a patient. This guide covers the two documents a clinic should separate, what each line means, how to verify a report, and what to ask for before ordering.

Status as of October 30, 2026. This is general education for clinicians, and your state board of pharmacy decides how these rules apply to you. A clean certificate does not make a product lawful: whether a peptide may be compounded at all is covered in our map of the FDA compounding categories.

Two documents people call a COA

Peptide quality gets tested at two points, and a certificate from one cannot stand in for the other.

A supplier's report on a powder tells you little about a sterile vial made from it weeks later. Ask for both.

What the law requires

Section 503A of the Federal Food, Drug, and Cosmetic Act says a compounder's bulk drug substances must come from an establishment registered with FDA and be "accompanied by valid certificates of analysis for each bulk drug substance." That duty sits on the pharmacy, so a 503A pharmacy should already hold this document for every lot it uses.

A 503B outsourcing facility works under current good manufacturing practice, which requires testing each batch of a drug product purporting to be sterile or pyrogen-free. Our guide to 503A vs. 503B pharmacies covers how the two models differ and what each may supply to a clinic.

Neither rule requires a pharmacy to hand you these documents. A pharmacy that shares them readily is easier to trust, and our compounding pharmacy guide covers the rest of that vetting.

How to read each line

Purity and potency are different numbers

The figure most people look for is the HPLC percentage, and it is the easiest to overread. HPLC purity compares the main peak with the other peaks the method detected, so a 99% result describes the proportion of signal in that sample. It does not state how many milligrams are in the vial, and water, salts, and anything the method cannot see do not lower it.

Potency answers the question a prescriber cares about: whether the vial holds the labeled amount. A powder can show high purity and still deliver less peptide than its nominal weight, since part of that weight may be water and counterion. Look for a separate assay or peptide content result on the bulk report, and a potency result on the finished preparation, stated against the pharmacy's acceptance range.

Impurities deserve attention as well as the headline percentage. FDA has raised peptide-related impurities and aggregation as a concern for immunogenicity in compounded peptides. Ask whether impurities were identified, or only added up into a remainder.

Sterility and endotoxin

A sterility test incubates a sample and looks for growth, and USP Chapter 71 calls for incubation of not less than 14 days. A report issued sooner than that after sampling needs an explanation. Sterility results also apply only to the batch tested, and a sample passing does not prove every vial in a batch is sterile, which is why aseptic technique and environmental controls matter too.

Endotoxin is a separate question. These fragments of bacterial cell walls can survive sterilization and cause fever and other reactions. USP Chapter 85 sets limits with the formula K/M, where K is 5 EU per kilogram for most non-intrathecal parenteral routes, and M is the maximum dose per kilogram given in an hour. For a 70 kg patient receiving a 1 mg dose, that works out to 350 EU per mg. The pharmacy should set the limit for its preparation, so ask how it was calculated if the report only says "pass."

How to verify a report

Treat a certificate as a claim until you can trace it.

Red flags on a peptide COA

"For research use only" printed anywhere on the document or the product means it was never intended for patients, whatever the results show, and our guide to research use only peptides explains why. A report with no lot number is another red flag, since it describes a product line and proves nothing about your vial.

Be wary of a purity figure with no method, a report with no limits beside its results, or identical results across different lots. Also question a certificate issued by the seller with no named lab, a PDF that the listed lab will not confirm, and any injectable sold with purity data alone. If a supplier's whole quality story rests on a purity percentage, sterility and endotoxin are still unanswered.

What to ask the pharmacy before ordering

A pharmacy that compounds peptides should be able to answer these in writing.

1. The bulk COA. Request it for the lot used, with the manufacturer's name and FDA registration.
2. Identity and purity methods. Ask which tests the pharmacy relies on, and whether it retests incoming substance or accepts the supplier's report.
3. Potency. Ask whether finished preparations are assayed, how often, and what range counts as passing.
4. Sterility and endotoxin. Ask for lot-level results, or the pharmacy's written testing schedule if each lot is not tested.
5. The beyond-use date. Ask what testing and stability data support the date on the label.
6. Out-of-specification results. Ask how the pharmacy handles a failed lot and how it would notify your clinic.

Keep what you receive with your purchasing records, linked to the lot numbers you log on arrival. If a product problem or serious adverse event occurs, those records make a report to FDA MedWatch far easier to complete. For what to do when a shipment arrives, including a warm one, see our guide to storing and handling compounded peptides.

Learning to source and prescribe peptides

Peptavo's peptide course for physicians covers sourcing and compounding alongside protocols and patient cases, and is designated for up to 20 AMA PRA Category 1 Credits™. The same course is open to nurses and nurse practitioners, who often manage ordering and receiving in a clinic.

Frequently asked questions

What is a certificate of analysis for peptides?

It is a lab record for one specific lot of a peptide, listing the tests performed, their limits, and the results. A complete report for a clinic's purposes covers identity, purity, and potency, plus sterility and endotoxin for an injectable preparation.

What purity should a peptide COA show?

Compare the result with the limit on the report and the standard the pharmacy works to, because no single number applies to every peptide. High purity alone is not enough, since it does not measure potency, sterility, or endotoxin.

How do I verify a peptide COA?

Match the lot number to your product, then contact the named lab directly with the report number, using contact details you found yourself. Check that the lab holds relevant accreditation and that the bulk manufacturer appears in FDA's registration database.

Does a compounded peptide need a certificate of analysis?

Section 503A requires bulk drug substances used in compounding to be accompanied by valid certificates of analysis. Finished preparations are tested under USP and state requirements, and their reports may look different, so ask the pharmacy what it tests.

Does a COA mean a peptide is safe or legal?

No. A certificate reports test results for one lot. Legal status depends on the substance and its source, and safety also depends on the patient, the dose, and how the product was handled.