What is Counterfeit Peptides? (Peptide Glossary)

Counterfeiting in the research peptide market ranges from underdosing (less peptide than labeled) to substitution (a cheap peptide sold as an expensive one) to outright fakes (vials containing mannitol or nothing active). The highest-risk compounds are the highest-demand ones: semaglutide, tirzepatide, and retatrutide currently top the counterfeiting charts precisely because demand and price are high.

Substitution is the sophisticated threat. A vendor selling 'tirzepatide' that is actually semaglutide - or a cheap short peptide - can pass casual inspection because the products look identical and even produce similar research observations at the gross level. Only mass spectrometry catches substitution, which is why MS identity confirmation is non-negotiable for expensive compounds.

The counterfeit defense stack: batch-specific third-party COAs with both HPLC and MS, vendor participation in community testing programs, prices within a plausible range of the synthesis cost floor, and community reputation verified across multiple independent sources. Vendors failing several of these checks simultaneously should be avoided regardless of how professional their website looks.