How to Verify Purity and Endotoxin on a Peptide CoA

To verify a peptide CoA, first match its lot number to the one on your vial. Then check four results: identity confirmed by mass spectrometry, purity by HPLC, the measured amount against the label, and endotoxin in EU below the limit set for that product. A purity number on its own proves little. In a lab study of semaglutide sold online without a prescription, one vial advertised 99% purity and tested at 7.70%. The CoA you can rely on most is tied to a prescription filled at a state-licensed pharmacy.

What should a peptide CoA test for?

A complete report covers five tests. Each one answers a different question about what is in your vial.

Identity and purity work as a pair. HPLC splits the sample into peaks, and mass spectrometry shows which peak is the peptide you paid for and which peaks are by-products of making it.

The amount line compares what the lab measured with what the label promises, and gives an allowed range. One compounding pharmacy's third-party report for 10 mg/mL tirzepatide, shared in r/tirzepatidecompound, listed a tested concentration of 9.9225 mg/mL, an assay of 99.2% and a specification of 90 to 110%, tested by HPLC.

The endotoxin test, set out in USP chapter 85 on bacterial endotoxins, uses a reagent made from horseshoe crab blood cells. Results come in Endotoxin Units (EU), and one EU equals one International Unit (IU), so you may see either.

Sterility is its own line. It tells you whether live microbes grew, not whether endotoxin is present. In the online semaglutide study, all three tested samples had no live microbes and still contained endotoxin.

How do I check the purity and dose numbers on a CoA?

1. Match the lot number. Find it on the report and on your vial. If they don't match, the report is about someone else's vial. One patient who asked their pharmacy for its reports wrote in r/tirzepatidecompound: "My vial is lot 574691, so my lot is specifically listed on that report."
2. Check the method. A purity percentage from HPLC alone can mislead, because a single big peak may or may not be the right peptide. Look for a mass spectrometry identity result as well.
3. Read purity and amount as two different numbers. In the lab study of semaglutide bought online without a prescription, one vial labeled 3 mg and 99% pure held 3.86 mg of semaglutide (28.56% over the label) at 7.70% purity, inside 50.1 mg of powder. That vial delivered more drug than labeled, and most of the powder was something else.
4. Check the range, the lab and the date. The amount should fall inside the specification range printed on the report, and the report should name the lab and the test date. A report with no range gives you nothing to judge the result against.

How do I read the endotoxin result on a peptide CoA?

Endotoxins are pieces of bacterial cell walls. They get into peptides easily when peptides are made in ordinary lab conditions, and they set off immune signals that can cause a wide range of reactions in the body. That is why the endotoxin line matters more for anything you inject.

A passing result is an endotoxin level below the limit set for that product. The report should state both the number and the limit. Check that the units (EU per mg or EU per mL) match the way your dose is measured.

Here is what real numbers look like. In the online semaglutide study, two vials tested below 2.8658 and 2.1645 EU/mg. A third measured 8.9511 EU/mg, which the researchers said pointed to possible contamination during production. The bacteriostatic water sent with the vials was a standard off-the-shelf product, so the contamination most likely came from the peptide itself.

A vial can be labeled sterile and still carry endotoxin. Sterilizing filters do not remove endotoxins, and once endotoxin is in a product it is hard to get out. The best fix is making the peptide clean from the start.

What can't a peptide CoA tell you?

A CoA covers one lot on the day it was tested. It cannot show what happened in shipping. FDA says not to use an injectable GLP-1 that arrives warm or without enough cold packs, and to throw out a multi-dose vial 28 days after first use, even if medicine is left.

The pharmacy named on a label or report can itself be fake. FDA has found compounded semaglutide and tirzepatide whose labels named pharmacies that don't exist, or licensed pharmacies that never made the product.

A product sold "for research purposes" or "not for human consumption" is a red flag no matter how clean its CoA looks. FDA has warned companies selling semaglutide, tirzepatide, retatrutide, survodutide or mazdutide under those labels, and urges consumers not to buy them because their quality is unknown.

You can pay an independent lab to check a vial yourself. Janoshik, for example, lists comprehensive purity and composition analysis of research peptides. That covers purity and composition, so it does not replace an endotoxin result, and it adds a lab bill to every vial you want checked.

Where can I get peptides with testing I can trust?

FDA's advice is to get a prescription from a licensed prescriber and fill it at a state-licensed pharmacy. FDA also lists a company that "does not require a screening and prescription by a licensed doctor" as a warning sign.

If you have questions about the instructions or label on a compounded medicine, FDA says to contact the compounder or the telehealth company. You can also ask them for the CoA for your lot. The pharmacy in the r/tirzepatidecompound thread sent lot-matched third-party reports when the patient asked. Those were potency results, so ask for endotoxin and sterility results too.

With a prescription, you don't have to be your own quality lab. Our clinical team reviews your goal and health history and decides whether a peptide fits your plan. If you want a peptide for your skin, recovery or energy without having to check lab reports yourself, take the quiz. Your clinical team will see which treatment fits your goal.