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Buyer's guide

How to tell if a peptide source is legit

Great sources love showing their receipts. Here's how to read a COA in two minutes, check it's real, and spot the red flags, so you know exactly what's in the vial.

Why it matters

Testing is the whole game, and the research shows why:

• Researchers bought semaglutide vials from illegal online pharmacies with no prescription and tested them. Every vial contained endotoxin (a bacterial contaminant), measured purity was 7.7% to 14.37% against the 99% claimed on the labels, and the semaglutide content was 28.56% to 38.69% above the labeled amount (Ashraf et al., J Med Internet Res, 2024, PMID 39509151).
• Melanotan II vials from three online shops each claimed 10 mg. Testing found 4.32 to 8.84 mg, and vials from two shops held 4.1% to 5.9% unknown impurities (Breindahl et al., Drug Test Anal, 2015, PMID 24771717).
• Obestatin bought from five manufacturers by research groups: one product was a totally different peptide, and two-thirds of the rest fell short of research quality (under 95% purity and/or single impurities over 1%). The authors recommend quality-control testing before using any peptide in research (De Spiegeleer et al., Anal Biochem, 2008, PMID 18342612).

What's on a good COA

A certificate of analysis (COA) is the lab report for one batch. Look for:

• Compound name and the amount the vial is supposed to hold.
• Batch or lot number that matches the number printed on your vial. A report for a different batch tells you nothing about yours.
• HPLC purity: high-performance liquid chromatography separates the sample and shows what share of it is the main compound, ideally with the chromatogram (the peak chart) attached.
• Mass spec identity: mass spectrometry checks that the main compound has the expected molecular mass, which means it's the right molecule. Purity alone can't tell you that. In the melanotan II study, identity was confirmed by mass spec, while LC-UV measured amount and impurities (Breindahl 2015, PMID 24771717).
• Amount per vial: measured content, so you know the vial holds what the label says.
• Endotoxin result for anything injectable, since endotoxin turned up in every vial in the semaglutide study above.
• The lab's name, the test date and a report number.

Third-party testing: what "independent" should mean

• A separate lab from the seller, named on the report, with real contact details.
• Accreditation is a plus. ISO/IEC 17025 is the international standard that lets testing labs show they work competently and produce valid results.
• Verify the report with the lab. Contact the lab named on the COA, or use its online lookup if it has one, and confirm the report number, compound, lot and results match.
• Fresh, batch-specific results. A new batch should come with its own report.

Red flags

• No COA, or "available on request" that never arrives.
• A COA with no lot number, no lab name, no date, or a lot number that doesn't match your vial.
• The same report reused across batches or products.
• Purity listed with no method, or HPLC purity with no identity check.
• A lab that can't be found or won't confirm the report.
• Prescription drugs sold without a prescription, prices that seem too good to be true, or no U.S. address and licensed pharmacist. These are the FDA's warning signs of an unsafe online pharmacy.

Approved drug? Use the pharmacy route

For FDA-approved medicines like semaglutide and tirzepatide, the FDA's checklist for a safe online pharmacy is simple. It requires a prescription, lists a U.S. address and phone number, has a licensed pharmacist to answer questions, and is licensed by a state board of pharmacy, which you can check through FDA's BeSafeRx tool. Getting dosed from a vial? Our mg-to-units calculator shows the math from your own label.

Next up: all our peptide guides, what retatrutide users report online, or Peptides 101.

Peptide source FAQ

Not medical advice. Education only. We don't sell anything or tell you what to take. Label doses are there so you can follow along with your prescriber. Talk to a licensed clinician about your health.