Quick answer: PT-141, also called bremelanotide, is a cyclic synthetic heptapeptide derived from the Melanotan II structure and studied as a melanocortin receptor agonist. The name is a development code, not a structural abbreviation. It is a laboratory research compound only. This explainer covers the name, structure, how it differs from Melanotan II, the preclinical research themes, and what to check on a certificate of analysis.
Where the name PT-141 comes from
PT-141 is a development code rather than a description of the molecule. It dates from the work of a biotechnology company, Palatin Technologies, that screened melanocortin-based peptides, and the code stuck in supplier catalogs. The nonproprietary name of the same molecule is bremelanotide, so you will see both names used for the same compound. A third label, “PT-141 peptide,” simply adds the word peptide.
The molecule is a cyclic heptapeptide with a molecular weight of about 1,025 g/mol (formula C50H68N14O10). It is written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. In plain terms: an acetylated norleucine at the front, then a ring formed by a lactam bond between the aspartic acid and lysine side chains, enclosing the core His-D-Phe-Arg-Trp sequence that melanocortin receptors recognize.
The chemistry is explained further in PT-141 chemical structure and synthesis, and the background in the discovery and history of PT-141.
How PT-141 relates to Melanotan II
The question buyers ask most is whether PT-141 and Melanotan II are the same. They are close relatives, not twins. PT-141 was derived from the Melanotan II structure: it keeps the cyclic lactam scaffold and the His-D-Phe-Arg-Trp core, but the C-terminal amide of Melanotan II is replaced by a free acid. That small change alters how the molecule is described chemically and affects receptor-binding comparisons in the literature.
Both belong to the melanocortin family, whose natural members include alpha-MSH, beta-MSH, gamma-MSH and ACTH. These share the His-Phe-Arg-Trp message sequence, which is why so many synthetic analogs carry it. If you want the family context, see KPV vs. alpha-MSH and the Melanotan II research overview.
What the preclinical literature examines
Everything in this section is preclinical or mechanistic. It describes what researchers measure, not outcomes in people, and it makes no claim of benefit.
Receptor pharmacology. PT-141 is described as a melanocortin receptor agonist. Binding and signaling assays in cell lines compare its activity across the receptor subtypes MC1R, MC3R, MC4R and MC5R. Reports generally describe stronger activity at MC3R and MC4R than the endogenous ligands show at the same receptors, along with activity at MC1R.
Central versus peripheral signaling. Melanocortin receptors are expressed in the central nervous system as well as in skin and other tissues. A recurring theme in the animal literature is that melanocortin agonists act through pathways in the brain, not only at the tissue level, which is one reason the receptor subtype matters when reading a paper.
Cyclization and stability. Because the ring is held by a lactam bond, researchers compare cyclic analogs with linear alpha-MSH fragments in terms of resistance to enzymatic breakdown and receptor selectivity. The cyclic design is a major reason these analogs are studied at all.
Interpretation caution: melanocortin receptors have overlapping roles, so an observation in one model may not carry to another, and receptor-subtype conclusions from cell lines do not automatically hold in tissue. Our mechanism of action article and preclinical research summary point to the primary sources.
PT-141 and related melanocortin peptides at a glance
The table lists descriptors only, to help you tell the names apart.
| Compound | Form | Origin | Notable feature |
|---|---|---|---|
| PT-141 (bremelanotide) | Cyclic heptapeptide, free C-terminal acid | Derived from Melanotan II | Lactam ring with N-terminal acetyl-norleucine |
| Melanotan II | Cyclic heptapeptide, C-terminal amide | Synthetic alpha-MSH analog | Same ring and core as PT-141 |
| Alpha-MSH | Linear 13-residue peptide | Natural, from POMC processing | Short-lived in biological media |
| KPV | Linear tripeptide (Lys-Pro-Val) | C-terminal fragment of alpha-MSH | Lacks the His-Phe-Arg-Trp core |
Handling the lyophilized powder
PT-141 is supplied as a freeze-dried powder. The general rules for lyophilized peptides apply: keep sealed vials cold, dry and away from light, limit warming and cooling cycles, and note the date a vial is first opened. The tryptophan and histidine residues make the molecule sensitive to light and oxidation over long periods, so storage conditions and time after opening are worth recording. Allow a cold vial to reach room temperature before opening it to limit condensation.
See PT-141 storage and handling for general notes.
What to check on a PT-141 certificate of analysis
Cyclic peptides are harder to make and to verify than linear ones. Incomplete ring closure or a linear precursor can sit very close to the target peak, so the paperwork matters.
HPLC purity with the chromatogram. Look at the full trace and at how minor peaks near the main peak were integrated. Understanding HPLC purity explains the numbers.
Identity confirmation. As general buying guidance, ask what method confirms a mass near 1,025 g/mol. A linear precursor has a mass about 18 units higher, because ring closure loses a molecule of water, so a mass-based method is what separates the two.
Lot reference and date that match your vial, and the name of the testing laboratory.
Fill amount and whether it refers to total powder or net peptide.
Use how to read a COA and PT-141 purity testing as checklists. For sourcing see where to buy PT-141, and for our listing see the PT-141 product page.
Common misunderstandings
“PT-141 and Melanotan II are the same compound.” They share a scaffold but differ at the C-terminus, and they are listed as separate molecules.
“PT-141 and bremelanotide are different products.” They are two names for one molecule: one a company code, the other the nonproprietary name.
“Regulatory status elsewhere applies to this vial.” A formulation or status the molecule has in another jurisdiction does not change that products sold by V8 Peptides are for laboratory research only.
“Animal data predicts human outcomes.” It does not, and this article makes no such claim.
Frequently asked questions
What is PT-141?
A cyclic synthetic heptapeptide, also called bremelanotide, derived from the Melanotan II structure and studied as a melanocortin receptor agonist.
What does PT-141 stand for?
It is a development code from the company that originally worked on it, not an abbreviation of the molecule’s structure.
Is PT-141 the same as bremelanotide?
Yes. Bremelanotide is the nonproprietary name for the same molecule.
How is PT-141 different from Melanotan II?
They share the cyclic lactam scaffold and core sequence, but PT-141 has a free C-terminal acid where Melanotan II has an amide.
What is PT-141’s molecular weight?
About 1,025 g/mol.
Which receptors does the literature associate with PT-141?
Melanocortin receptors, mainly discussed in terms of MC3R and MC4R activity, with activity at MC1R also reported.
Is PT-141 approved in the United States?
A pharmaceutical form of the molecule exists elsewhere under its own regulatory status. V8 Peptides sells PT-141 for laboratory research use only, not for human or animal consumption.
Why is cyclization relevant to a COA?
A linear precursor and the closed ring differ in mass by about 18 units, so a mass-based identity method is what distinguishes them.
What should I look for on a PT-141 COA?
An HPLC chromatogram, an identity method that confirms the expected mass, a lot reference matching your vial, a test date and a named laboratory.
How is lyophilized PT-141 stored?
Sealed, cold, dry and protected from light, with temperature cycling avoided and the opening date recorded.
All V8 Peptides products are sold for laboratory research use only. They are not drugs, foods, or cosmetics and are not intended for human or animal consumption.
References
- Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides. 2006;27(4):921-930.
- Cone RD. Studies on the physiological functions of the melanocortin system. Endocrine Reviews. 2006;27(7):736-749.