PT-141, explained: the cyclic peptide also called bremelanotide

PT-141 is bremelanotide. Same molecule, two names: PT-141 is the code it carried in development, bremelanotide is its international non-proprietary name. It is a small, ring-closed peptide from the melanocortin family, built on a fragment of a hormone called alpha-MSH, and it is a very close chemical relative of melanotan II.

What the molecule is

You've probably seen "PT-141" written as if it were a brand. It is just a code. PubChem lists PT-141, PT 141 and PT141 as synonyms of bremelanotide, compound CID 9941379.

The structure, as both PubChem and the FDA label give it:

Two terms worth unpacking. Nle is norleucine, an amino acid not found in the body's own proteins. A lactam bridge is an amide bond made between two side chains rather than along the backbone, which closes six of the seven residues into a ring.

One practical detail from the FDA label: the approved drug substance is bremelanotide acetate, with one to two acetate counter-ions per molecule. The 1,025.2 figure is the free base. That distinction matters later, when we get to quantity.

Where it came from: alpha-MSH, then melanotan II

Alpha-MSH (alpha-melanocyte-stimulating hormone) is a 13-residue peptide: Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, according to PubChem. Positions 6 to 9, His-Phe-Arg-Trp, are the stretch the melanocortin receptors recognise.

Melanotan II was built on positions 4 to 10 of that hormone. Dorr and colleagues described it in 1996 as a lactam-bridged cyclic heptapeptide analogue of alpha-MSH, numbered against positions 4 to 10. Set beside the hormone's sequence: methionine 4 swapped for norleucine, glutamic acid 5 for aspartic acid, phenylalanine 7 for its mirror-image D form, glycine 10 for lysine, and a ring closed between residues 5 and 10.

Bremelanotide is that same ring with one change at the tail. Lay the PubChem records side by side:

A 2026 review of melanocortin-4 receptor drug development by Feng, Zhou and Wang describes bremelanotide as a deaminated derivative of melanotan II, one that may represent a metabolite of melanotan II in humans. In plain terms: take the amide off the end of melanotan II, leave a carboxylic acid, and you have bremelanotide.

The same hormone gives rise to a much smaller research compound. KPV is the C-terminal tripeptide of alpha-MSH, its last three residues. KPV belongs to no other family in this catalogue, and neither does MOTS-c; the two are compared in MOTS-c and KPV: two research peptides that fit no family.

Which receptors it binds

There are five melanocortin receptors, MC1R to MC5R. They are G-protein-coupled receptors, and each responds to peptides from the alpha-MSH family to a different degree.

Bremelanotide is not selective. The FDA label describes it as a melanocortin receptor agonist that "nonselectively activates several receptor subtypes", and gives the order of potency as:

MC1R > MC4R > MC3R > MC5R > MC2R

The structural detail has been seen directly. Zhang and colleagues published cryo-electron microscopy structures of the melanocortin-4 receptor in Cell Research in 2021, one of them with bremelanotide bound, at 3.1 Å resolution (Protein Data Bank entry 7F55). The 2026 review by Feng and colleagues summarises those structures: alpha-MSH and the peptide drugs built from it share a U-shaped binding pose, reaching deep into the receptor's binding pocket through the conserved His-Phe-Arg-Trp motif.

Development and regulatory status

The development history, by date:

• 2006: the earliest bremelanotide study registered on ClinicalTrials.gov began in February that year.
• 2014 to 2017: two phase 3 trials, registered under the name Reconnect, ran in the US and Canada (designs below).
• 21 June 2019: the FDA approved bremelanotide under NDA 210557, classed by the agency as a Type 1 new molecular entity. In the label's words, the approved indication is "the treatment of premenopausal women with acquired, generalized hypoactive sexual desire disorder (HSDD)", with further conditions set out in the label itself.

Dhillon and Keam's 2019 profile in Drugs, "Bremelanotide: First Approval", covers the milestones in more detail.

In the UK, we found no marketing authorisation. A search of the MHRA products database for bremelanotide on 27 October 2026 returned no results, and bremelanotide does not appear in the MHRA's substance index. The European Medicines Agency's published list of medicines, which includes refused and withdrawn applications as well as authorised ones, contains no bremelanotide product. You can repeat the MHRA search yourself on the products database. An FDA approval does not carry over to the UK. What "approved", "licensed" and "neither" each mean.

The registered trials, by design

ClinicalTrials.gov lists ten studies with bremelanotide as an intervention (searched 27 October 2026). The three phase 3 trials are set out below by how they were built. We give design only: no results, no figures on outcomes or adverse events. The NCT links go to the registry records, where the registered outcome measures are listed.

All three registered the same population: premenopausal women, aged 18 or over in the two Reconnect trials and 19 or over in the Korean bridging trial, with the condition named in the FDA indication.

Two things worth noticing. The Reconnect pair were built as twins: two trials registered with the same design and run in parallel, so each is a check on the other. And "triple-masked" is the registry's term for the participants, the investigators and the outcome assessors all being kept unaware of who received what.

The registry also lists bremelanotide studies outside the approved indication, among them a phase 2 study in diabetic kidney disease and a phase 2 study combining it with tirzepatide. Those are registrations, not findings.

What matters for research supply

Three points, specific to this molecule.

1. Identity, by mass spectrometry. Bremelanotide and melanotan II sit 0.98 Da apart: monoisotopic masses of 1,024.524 and 1,023.540 Da on PubChem. Same ring, same residues, one end group different. Their nominal masses differ by a single unit, so the mass check has to be precise enough to separate them. Mestria and colleagues did exactly this in 2021, using high-resolution Orbitrap mass spectrometry to characterise melanotan II and bremelanotide in seized samples without reference standards. A report should show the observed mass and the method. How HPLC-MS identity and purity work.
2. Quantity is a separate number from purity. A 99% purity figure says nothing about how many milligrams are in the vial. For bremelanotide there is a second question: whether a stated amount refers to the free base or to the acetate salt, since the counter-ions add mass. Why 99% pure is not 10 mg.
3. Storage. 2 to 8°C, dark, not frozen. The reasons behind each of those.

For laboratories, PT-141 10 mg is listed as coming soon, with an independent Janoshik report to be published for each batch, supplied strictly for in-vitro laboratory research.