Independent analysis puts a SWB tirzepatide lot at 95.6%, against 93.1% on the certificate

An independent purity determination on tirzepatide material sold by SWB has returned 95.6%, a figure 3.7 percentage points below the number printed on the accompanying certificate. The analysis was performed by VendorInvestigate on a vial the Journal bought as an ordinary retail customer in August 2025 and posted unopened.

The Journal purchased 1800 vials from the same lot and had 12 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 95.6%, lowest 93.1%, median close to the midpoint of the two. Every report in the set stated a detection wavelength, and 12 of them stated an integration threshold. The Journal has asked the laboratory to publish thresholds on all reports as a matter of routine.

Discrepancies of one to two percentage points between a supplier’s figure and an independent determination are common and usually explicable: a faster gradient resolves fewer impurities, a higher integration threshold discards more small peaks, and a wider solvent-front exclusion window removes early-eluting fragments from the calculation altogether. None of that is misconduct. All of it is invisible unless the method is disclosed.

Yusuf Kandemir, freight and customs broker, Istanbul, said the gap was predictable from the methods alone. "You can reconstruct almost the whole difference from the integration threshold. What you cannot reconstruct is why anyone thinks a number without a threshold is comparable to a number with one."

SWB’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.