PT-141 is the development code of bremelanotide, a synthetic cyclic peptide of seven building blocks. It is a melanocortin receptor agonist: it binds to the same receptors as the body’s own hormone alpha-MSH [1][2]. Bremelanotide was developed by the US company Palatin Technologies as a derivative of melanotan II [3]. In 2019 the US FDA approved bremelanotide as a prescription medicine under the brand name Vyleesi, for one narrowly defined indication [1]. In the European Union there is no marketing authorisation [4]. Below you can read how the molecule is built, how it relates to melanotan II and what the regulations say.
Melanocortins and their receptors
Melanocortins are a family of peptide hormones cut from the same precursor protein. Well-known members are ACTH and alpha-MSH (alpha-melanocyte-stimulating hormone). They act through five receptors, MC1R to MC5R, which occur in different tissues. MC1R is found, among other places, on pigment cells in the skin. MC3R and MC4R occur mainly in the central nervous system.
According to the US prescribing information, bremelanotide is a non-selective agonist. It activates several receptor subtypes, in decreasing order of potency: MC1R, MC4R, MC3R, MC5R and MC2R [1]. The same prescribing information states that the exact mechanism for the approved use is unknown [1].
Structure and identity
| Feature | Bremelanotide (PT-141) |
|---|---|
| Substance class | synthetic cyclic heptapeptide, melanocortin receptor agonist |
| Structure | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH |
| Notable features | ring between aspartic acid and lysine, one D-amino acid (D-Phe), norleucine (Nle) at the start, free acid at the end |
| Molecular formula | C50H68N14O10 (PubChem CID 9941379) |
| Molar mass | 1025.2 g/mol (free base) |
| Salt form in the medicine | acetate |
The data come from the US prescribing information and PubChem [1]. Cyclic melanocortin analogues like this were designed to be more resistant to enzymatic breakdown than the natural hormone [3].
How it relates to melanotan II
Researchers at the University of Arizona developed two synthetic analogues of alpha-MSH: melanotan I, a linear chain, and melanotan II, a smaller cyclic variant [3]. Palatin Technologies developed bremelanotide as a new analogue of melanotan II [3].
The structural difference between the two is small. Melanotan II ends in an amide (-NH2), bremelanotide in a free acid (-OH). The ring structure is otherwise the same. As a result, their masses differ by only about one dalton: 1024.2 g/mol for melanotan II versus 1025.2 g/mol for bremelanotide (PubChem CID 92432 and 9941379).
Their regulatory status, however, differs sharply. Melanotan II has no marketing authorisation as a medicine, neither in the EU nor in the US [4][5]. Melanotan I, under the substance name afamelanotide, is authorised in the EU, for a specific indication unrelated to PT-141 [4]. Clean Peptides does not supply melanotan I or II.
Regulatory status: US, EU and WADA
United States. The FDA approved bremelanotide on 21 June 2019 as Vyleesi (NDA 210557). The approval covers one specifically defined indication in adults [1]. Palatin Technologies ran the phase 3 studies; for North America, the product was licensed to AMAG Pharmaceuticals [2]. According to the FDA’s US drug database, the authorisation is now held by Cosette Pharmaceuticals. Outside that indication, it is not an approved product in the US.
An approval applies to one specific product: made under pharmaceutical manufacturing rules, with a fixed composition and fixed product information. It says nothing about other uses and nothing about products that were not made under those rules.
European Union. Bremelanotide and Vyleesi do not appear in the medicines overview of the European Medicines Agency (EMA), which also includes withdrawn applications [4]. There is therefore no central EU authorisation, and no application to the EMA is known.
Sport. WADA’s 2026 Prohibited List does not name bremelanotide or melanotan II. The list uses open groups; whether a substance falls under one of them is for the anti-doping organisations to decide.
PT-141 from Clean Peptides is a research material (research use only). It is not the same as the registered medicine and is not intended for use in humans or animals.
Analysis and storage
- Identity. Mass spectrometry (MS) must be able to distinguish bremelanotide from melanotan II. The difference is small (about one dalton), but readily measurable with accurate MS. Forensic laboratories in Italy used high-resolution MS for this on seized samples, in which both melanotan II and bremelanotide were found [5]. This shows how important an identity check is for these substances.
- Purity. HPLC shows which share of the signal belongs to the main peak. See How to read a certificate of analysis (COA).
- Sensitive building blocks. Tryptophan and histidine can oxidise; this produces extra peaks with a higher mass.
- Storage. As freeze-dried powder: dry, cool and dark. See Storing peptides.
Every Clean Peptides vial has a batch number on the label. Record it with every experiment.
Products and further reading
Products
PT-141 10 mg is supplied as freeze-dried powder in a vial. Solvent for the lab: bacteriostatic water 3 ml or 10 ml.
Further reading
- What are peptides? Key terms explained
- Research use only (RUO)
- How to read a certificate of analysis (COA)
- Knowledge base: peptides and research materials explained
Sources
- U.S. Food and Drug Administration. Vyleesi (bremelanotide), Prescribing Information, NDA 210557 (2019). accessdata.fda.gov (accessed 6 October 2026)
- Dhillon S, Keam SJ. Bremelanotide: first approval. Drugs 2019;79(14):1599–1606. doi:10.1007/s40265-019-01187-w
- Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides 2006;27(4):921–930. doi:10.1016/j.peptides.2005.01.029
- European Medicines Agency. Download medicine data, medicines overview including withdrawn applications (accessed 6 October 2026)
- Mestria S, Odoardi S, Frison G, Strano Rossi S. LC-HRMS characterization of the skin pigmentation and sexual enhancers melanotan II and bremelanotide sold on the black market of performance and image enhancing drugs. Drug Testing and Analysis 2021;13(4):876–882. doi:10.1002/dta.2986
For laboratory research only. Clean Peptides products are not intended for use in humans or animals. This article provides general information and is not medical advice.
