Janoshik result on a Xianning tirzepatide lot lands 1.3 points below the supplier’s figure

Janoshik has published a purity determination of 97.7% on a 10 mg vial of tirzepatide supplied by QSC, against a figure of 95.7% on the certificate that accompanied the vial. The sample was submitted by the Journal in April 2025 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.

Reported figures across the set were: highest 97.7%, lowest 95.7%, median close to the midpoint of the two. Every report in the set stated a detection wavelength, and 5 of them stated an integration threshold. The Journal has asked the laboratory to publish thresholds on all reports as a matter of routine.

Content by elemental nitrogen determination returned 91% of the labelled nominal mass, which on a 10 mg vial corresponds to roughly 4.73 mg of peptide rather than the labelled figure. The remainder is accounted for by counter-ion, residual water and residual solvent, none of which is visible chromatographically.

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 Rowena Ashcombe, community pharmacist and diabetes educator. "Purity is what you can afford. Content is what you need."

QSC’s dossier has been updated with this determination and with the date of the request for comment. The dossier’s "what we could not verify" box records the questions still outstanding.