PT-141 — identity, purity, and the cyclic-peptide question.

The biological activity of PT-141 depends on the cyclic conformation. The linear ring-opened form has the same amino acid sequence but with the ring hydrolyzed open (+H₂O); receptor binding affinity is significantly reduced. Visual inspection of a vial cannot distinguish cyclic vs linear PT-141. LC-MS, which catches the +18 Da difference, is the tool that identifies which form is in the vial.

Both are melanocortin receptor agonists, but PT-141 (Bremelanotide, 7-residue) is FDA-approved as Vyleesi for hypoactive sexual desire disorder. Melanotan II (similar 7-residue cyclic peptide with a different sequence) is not FDA-approved and is marketed as a tanning peptide. Different sequence, different receptor selectivity, different pharmacology. LC-MS distinguishes them by molecular ion mass.

Industry-typical 78-88 %. Below 75 % indicates excess counter-ion or residual moisture. Above 90 % is uncommon for TFA-salt material. NPC is the dose-accuracy metric independent of HPLC purity.

Yes — compounded PT-141 from compounding pharmacies has wide variability across compounders. We've tested batches from major US compounding pharmacies that ranged 88-97 % HPLC purity. The compounder's certificate of analysis is generally reliable, but independent verification matters when dose accuracy or safety is critical.

Purity ($199): single 5 mg sealed lyophilized vial. Identity + Potency ($499): same single vial. Full Disclosure ($899): two additional vials for the destructive sterility and endotoxin tests. Send original sealed vials by overnight courier.

Yes. Ship the reconstituted vial cold-packed in original BAC water or sterile saline. Reconstituted material is what the user actually exposes themselves to, so testing it directly is the most meaningful version of the assay. Pricing matches the lyophilized vial panel.