Evaluating GLP-1 peptide vendors — what to demand on the COA

Counterfeit and underdosed semaglutide and tirzepatide are real problems in the research-grade peptide supply chain right now. The class has gotten so much attention that demand far exceeds the legitimate manufacturing capacity, and that gap creates economic incentives for low-quality product to enter the market. This thread covers what to look for on a Certificate of Analysis specifically for GLP-1 peptides — beyond the general COA-reading skills covered in the COA & Lab Results category.

Why GLP-1 peptide quality is harder to verify than smaller peptides.
Semaglutide and tirzepatide are larger and more structurally complex than peptides like BPC-157 or ipamorelin. Semaglutide is 31 amino acids with a fatty acid side chain. Tirzepatide is 39 amino acids with similar lipidation. Larger peptides are harder to synthesize cleanly — the percentage of synthesis byproducts goes up with chain length, and the side-chain modifications add another vector for incomplete or incorrect product. This is the technical reason the COA quality bar should be higher for this class than for shorter peptides.

The non-negotiables on a GLP-1 peptide COA.

HPLC purity above 98%. For shorter peptides, 97% is generally acceptable. For semaglutide and tirzepatide, the expectation should be 98% minimum and ideally 99%+. The 1-2% difference matters because the impurities in synthesis byproducts of these larger molecules include truncated sequences with related but altered receptor activity. A 95% pure product where the remaining 5% is a 30-amino-acid truncation with unknown activity is not acceptable for serious research.

Mass spectrometry confirmation. HPLC tells you how pure the dominant peak is — it does not tell you the dominant peak is the molecule it claims to be. Mass spec confirms identity. For semaglutide, the theoretical molecular weight is 4113.58 Da. For tirzepatide, it is 4813.5 Da. The observed mass on the COA should match within a narrow margin. This is the single most important check for ruling out a counterfeit where the wrong peptide is being labeled as semaglutide or tirzepatide.

Specific batch number matching the vial. Generic COAs reused across batches are a major red flag for this class. The high demand creates incentive to attach a single legitimate COA to many subsequent batches that were never tested. The batch number on the document must match the batch number on the vial.

Named third-party lab with verifiable accreditation. Look for ISO 17025 accreditation. The lab should be findable on a basic web search and should have a public report-verification process. If the COA names a lab and the lab cannot be verified independently, treat the COA as fabricated.

Specific things that distinguish high-quality GLP-1 vendors.

• Quantitative content testing. Beyond purity percentage, some labs measure actual peptide content per vial. A 5mg vial that contains 5mg of pure peptide is not the same as a 5mg vial that contains 3mg of 99% pure peptide. Underdosing is the most common quality issue with this class and quantitative content testing is the most reliable way to catch it from documentation.
• Endotoxin testing. For injectable research, endotoxin levels should be reported with a value below the standard threshold (less than 5 EU/mg). Missing endotoxin testing is a quality gap, not necessarily a deal-breaker, but a vendor doing it signals higher overall standards.
• Multi-batch consistency. If you can compare COAs across multiple batches from the same vendor, the purity and mass spec values should vary slightly batch-to-batch. Identical numbers across batches is statistically suspicious — it suggests a single COA is being recycled.

Red flags specific to this class.

• COA shows 99.0% purity on every single batch with no variation
• Mass spec section is missing or shows a value not matching the theoretical weight for the labeled compound
• Batch number on the COA does not match what is on the vial
• Lab name is unverifiable or the report number cannot be confirmed with the lab directly
• Vendor cannot answer specific questions about who synthesizes the product or where it is stored
• Price is dramatically below market — synthesis cost for these compounds is real, and vendors selling at half the going rate are either operating at a loss (rare and short-lived) or selling counterfeit (common)

What a strong GLP-1 vendor COA looks like in practice.
Specific batch number matching the vial. HPLC purity above 98% with chromatogram showing one dominant peak. Mass spectrometry confirming the theoretical molecular weight. Endotoxin testing below threshold. Named, accredited third-party lab with a verifiable report number. Quantitative content if available.

If you are evaluating a new vendor for any GLP-1 peptide, ask for the COA before you order. Compare it against the checklist above. If anything is missing or does not add up, walk away — there are enough vendors in this space that you do not need to gamble on a questionable one. Post specific COAs in this thread or the broader COA discussion threads if you want a second pair of eyes.