Published · 7 references
Melanotan II vs PT-141
Melanotan II and PT-141 are not the same molecule; PT-141 is Melanotan II with its C-terminal amide replaced by a free acid, carrying the identical lactam ring.
Structure at a glance
Drawn from the product database. Each measure's bars share one scale.
| Property | Melanotan II | PT-141 |
|---|---|---|
| What it is | A synthetic cyclic heptapeptide and analog of alpha-melanocyte-stimulating hormone, its ring closed by a lactam bridge. | Bremelanotide: a synthetic cyclic heptapeptide lactam and analog of alpha-melanocyte-stimulating hormone, derived from Melanotan II. |
| How they relate | PT-141 is a chemically modified form of Melanotan II. It is Melanotan II with its C-terminal amide replaced by a free acid, and carries the identical lactam ring. | |
| CAS number | 121062-08-6 | 189691-06-3 |
| Molecular formula | C50H69N15O9 | C50H68N14O10 |
| Molecular weight | 1024.18 g/mol | 1,025.17 g/mol |
| Sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys] |
| Target | Agonist at the MC1R, MC3R, MC4R and MC5R melanocortin receptors, in laboratory structure-activity work.[1] | A nonselective agonist at several melanocortin receptor subtypes, as described in human regulatory labeling.[2] |
| Evidence base | Receptor findings in the literature reviewed for Melanotan II come from in vitro and animal studies. Three published human studies, 1996 to 2000, with 3, 10 and 10 participants, all came from the group that designed the molecule. | Two phase 3 trials randomized 1,267 participants and supported an approval for one indication. The pivotal publications name employees of the two companies that funded them as authors. In the literature reviewed for PT-141, no sponsor-independent replication of those trials was identified. |
| Regulatory status | Melanotan II has no US approval.[3] | Bremelanotide acetate is the active ingredient of a prescription medicine sold under another name.[4] The material supplied here is a research-grade preparation, is not that medicine, and holds no marketing authorization. That medicine holds a current US approval for one therapeutic indication. |
| Compared head-to-head? | No direct comparison found in PubMed (searched October 2026).[5] | |
| Handling difference | Both rings are closed by an amide bond, and neither contains sulfur. | |
How Melanotan II and PT-141 differ
Melanotan II and PT-141 are not the same molecule. PT-141 is bremelanotide, which is Melanotan II with its C-terminal amide replaced by a free acid. The systematic name of Melanotan II ends in carboxamide, and that of PT-141 ends in carboxylic acid. PubChem lists the two as separate records.
The two share the same cyclic scaffold and terminate differently. In Melanotan II, a lactam bridge between the side chains of its aspartate and lysine residues closes the ring. PT-141 carries the identical lactam ring. Al-Obeidi and colleagues reported the cyclic lactam design behind Melanotan II in 1989.[6] Melanotan II was built from part of alpha-melanocyte-stimulating hormone (alpha-MSH), and PT-141 was derived from Melanotan II.
In 2021, Zhang and colleagues reported cryo-electron microscopy structures of a human melanocortin receptor.[7] In the literature reviewed for Melanotan II, the cyclic lactam peptide resolved in that study was bremelanotide. The three published human studies reviewed for Melanotan II tested Melanotan II, and all came from the group that designed the molecule. The two phase 3 trials reviewed for PT-141 tested bremelanotide. The searches behind the literature reviewed for PT-141, run in PubMed and ClinicalTrials.gov on 2 October 2026, identified no sponsor-independent replication of those trials.
Their regulatory positions differ. Bremelanotide acetate is the active ingredient of a prescription medicine sold under another name.[4] The material supplied here is a research-grade preparation, is not that medicine, and holds no marketing authorization. That medicine holds a current US approval for one therapeutic indication. Melanotan II has no US approval.[3] Neither compound's status transfers to the other.
In the laboratory, a low-resolution mass measurement will not reliably tell the two apart. An amide and a free acid differ in charge, and chromatography separates them on that basis.
Have Melanotan II and PT-141 been compared directly?
No direct comparison found in PubMed (searched October 2026).[5] That search covers PubMed only.
Read more on each compound
Melanotan II
Frequently Asked Questions
Is Melanotan II the same as PT-141?+−
Melanotan II and PT-141 are not the same molecule. PT-141 is bremelanotide, which is Melanotan II with its C-terminal amide replaced by a free acid, and it carries the identical lactam ring. PubChem lists them as separate records.
Is Melanotan II or PT-141 approved?+−
Melanotan II has no US approval. Bremelanotide acetate is the active ingredient of a prescription medicine sold under another name. The material supplied here is a research-grade preparation, is not that medicine, and holds no marketing authorization. That medicine holds a current US approval for one therapeutic indication.
References
- 1Hruby VJ, Lu D, Sharma SD, Castrucci AM, Kesterson RA, Al-Obeidi FA, et al. Cyclic lactam alpha-melanotropin analogues with bulky aromatic amino acids at position 7 show high antagonist potency and selectivity at specific melanocortin receptors. J Med Chem. 1995;38(18):3454-61. doi:10.1021/jm00018a005. PMID 7658432.
- 2US Food and Drug Administration. Prescribing information for the approved bremelanotide acetate product, section 12.1 (mechanism of action); label version of 13 November 2025. DailyMed set ID f1d0c1b5-2f39-4bad-a6a4-0066e3ad5dcf. dailymed.nlm.nih.gov
- 3US Food and Drug Administration, Drugs@FDA. Query of api.fda.gov/drug/drugsfda.json on openfda.substance_name "MELANOTAN II" returned no match, 3 October 2026.
- 4US Food and Drug Administration, Drugs@FDA. Approval record whose active ingredient is bremelanotide acetate; marketing status Prescription. Retrieved via api.fda.gov/drug/drugsfda.json on products.active_ingredients.name "BREMELANOTIDE ACETATE", 3 October 2026; one record returned.
- 5PubMed search via NCBI E-utilities, run 3 October 2026; records entered to 2 October 2026. Query: ("Melanotan II"[tiab] OR "Melanotan-II"[tiab] OR "Melanotan 2"[tiab] OR "Melanotan-2"[tiab] OR "MT-II"[tiab] OR "MTII"[tiab] OR "MT II"[tiab] OR "MT-2"[tiab]) AND ("PT-141"[tiab] OR "PT141"[tiab] OR "PT 141"[tiab] OR "bremelanotide"[tiab]) AND ("1800/01/01"[edat] : "2026/10/02"[edat]). 8 records; none was a direct comparison of the two compounds.
- 6Al-Obeidi F, Castrucci AM, Hadley ME, Hruby VJ. Potent and prolonged-acting cyclic lactam analogues of alpha-melanotropin: design based on molecular dynamics. J Med Chem. 1989;32(12):2555-61. doi:10.1021/jm00132a010. PMID 2555512.
- 7Zhang H, Chen LN, Yang D. Structural insights into ligand recognition and activation of the melanocortin-4 receptor. Cell Res. 2021;31(11):1163-75. doi:10.1038/s41422-021-00552-3. PMID 34433901.