PT-141, also called bremelanotide, is a synthetic melanocortin-family peptide of seven amino acids, built as a closed ring. It shares the melanocortin and dermal research collection with its close structural cousins.
Vestrand keeps it as one lot at a time, made ready for outside purity testing, with the finished certificate posted to its verification page.
Like others in its collection it is a ring rather than a straight chain, and it sits close enough to a neighbouring melanocortin compound that the two are easy to mix up by name alone. That is exactly why the per-lot certificate, tied to the specific vial, is the thing to rely on rather than the label.
For laboratory research use only. Not for human or veterinary use.