Independent analysis puts a ERP tirzepatide lot at 98.1%, against 95.1% on the certificate

Janoshik has published a purity determination of 98.1% on a 15 mg vial of tirzepatide supplied by ERP, against a figure of 95.1% on the certificate that accompanied the vial. The sample was submitted by the Journal in January 2026 as part of a continuing programme of arm’s-length purchasing, and the vendor was told before the order was placed that any result would be published.

The Journal purchased 17 vials from the same lot at retail and had four of them analysed separately, in order to distinguish vial-to-vial variation from method variation. Vial-to-vial agreement was within 0.4 percentage points. Method-to-method disagreement was an order of magnitude larger.

Reported figures across the set were: highest 98.1%, lowest 95.1%, median close to the midpoint of the two. Every report in the set stated a detection wavelength, and 19 of them stated an integration threshold. The Journal has asked the laboratory to publish thresholds on all reports as a matter of routine.

Four independent services — Janoshik, VendorInvestigate, and the two others operating in this market — carry the analytical burden for a trade that has no release-testing obligation of its own. Each is paid by whoever submits the sample, which is usually the vendor. The Journal’s position is that a submitter-pays model is workable but that its incentive structure has to be stated whenever a result is quoted as verification.

"Content is the number that matters if you are doing arithmetic with a vial, and content is the number nobody sells," said Dr Wenjun Xie, process chemist and peptide manufacturing consultant. "Purity is what you can afford. Content is what you need."

ERP’s dossier has been updated with this determination and with the company’s response to it. The dossier’s ordering box records the lead times, the minimum quantities and what a buyer should ask for at the point of order.