VendorInvestigate result on a Hong Kong retatrutide lot lands 2.9 points below the supplier’s figure

VendorInvestigate has published a purity determination of 97.8% on a 2 mg vial of retatrutide supplied by WXT, against a figure of 95.9% on the certificate that accompanied the vial. The sample was submitted by the Journal in March 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.

Content by elemental nitrogen determination returned 91% of the labelled nominal mass, which on a 2 mg vial corresponds to roughly 5.84 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.

The Journal purchased 3400 vials from the same lot and had 19 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.

Four independent services — VendorInvestigate, PeptideMeter, 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.

"The figure is not wrong and neither is theirs," said Sinéad Corrigan, patient advocate and former trial participant. "They are answers to two different questions and the trade has decided to pretend there is only one question. Print the gradient and the argument disappears."

WXT’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.