PT-141 is a synthetic cyclic heptapeptide, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, that is the C-terminal carboxylic-acid analogue of Melanotan II and has been described as a metabolite of that peptide. It retains the parent's Asp–Lys side-chain lactam bridge, N-terminal acetyl-norleucine and D-phenylalanine, differing only in lacking the C-terminal amide. Its international nonproprietary name is bremelanotide.

PT-141 is reported to act as an agonist at melanocortin receptors, with most attention given to MC3R and MC4R; activity at MC1R has also been described. These class A GPCRs signal predominantly through Gs and cyclic AMP. A 2021 cryo-EM study resolved the MC4R–Gs complex bound to PT-141, showing its His-D-Phe-Arg-Trp pharmacophore inserted into the orthosteric pocket in a binding mode conserved among peptide agonists.

PT-141 is used in melanocortin receptor pharmacology, including binding and cAMP assays in recombinant cell lines, comparative studies of cyclic lactam melanocortin peptides, GPCR structural biology, and neuropeptide receptor signalling in hypothalamic models. Its close relationship to Melanotan II allows comparison of the C-terminal amide and free-acid forms in receptor assays.

Research use only. This material is sold for in-vitro laboratory research and development purposes exclusively. It is not a drug, food, or dietary supplement, has not been evaluated by the FDA, and must not be used in humans or animals.