PT-141 vs Melanotan II: What's the Difference?
One group at one end. PT-141 (bremelanotide) and Melanotan II share the same seven-residue cyclic sequence, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys], and differ only at the C-terminus.
Melanotan II ends in an amide (-NH2): C50H69N15O9, 1024.2 g/mol. PT-141 ends in a free carboxylic acid (-OH): C50H68N14O10, 1025.2 g/mol. The two are about 1 g/mol apart.
History: Melanotan II was designed at the University of Arizona in the late 1980s; PT-141 was later developed from it by Palatin Technologies.
At Clean Peptide the two also come in different forms with different certificates: Melanotan II as a 10 mg powder vial with an ILS Laboratories full panel, PT-141 as a 20 mg in 20 mL spray solution with a HYTE Research Division identity and quantity certificate.
PT-141 vs Melanotan II at a Glance
PT-141 and Melanotan II have the same ring and the same seven residues. Melanotan II carries a C-terminal amide (C50H69N15O9, 1024.2 g/mol); PT-141 carries a free carboxylic acid (C50H68N14O10, 1025.2 g/mol). Swapping -NH2 for -OH is the only structural difference.
| Comparison | PT-141 | Melanotan II |
|---|---|---|
| Peptide length | 7 amino acids (cyclic) | 7 amino acids (cyclic) |
| Molecular weight | 1025.2 g/mol | 1024.2 g/mol |
| Sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 |
| Molecular relationship | Free-acid analogue of Melanotan II | Cyclic lactam analogue of alpha-MSH(4-10) |
| Main research focus | Melanocortin receptor agonist | Non-selective melanocortin receptor agonist (MC1R, MC3R, MC4R, MC5R) |
What are PT-141 and Melanotan II
7 AA • acid
PT-141
Bremelanotide, development code PT-141: a cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone with an acetylated N-terminus, norleucine in place of methionine, one D-amino acid (D-phenylalanine) and a lactam bridge between the aspartate and lysine side chains. Its C-terminus is a free carboxylic acid.
Research areas
Melanocortin receptor binding • Structure of cyclic alpha-MSH analogues
Clean Peptide's PT-141 is sold as a solution, 20 mg in a 20 mL spray bottle, for laboratory research only. PubChem CID 9941379.
Explore PT-141 Spray7 AA • amide
Melanotan II
MT2 or MT-II for short: the same cyclic heptapeptide built on the 4-10 fragment of alpha-MSH, with an amide at the C-terminus. It came out of a series of cyclic lactam melanotropins designed at the University of Arizona by Al-Obeidi, Hruby, Hadley and colleagues.
Research areas
Cyclic lactam design • Melanocortin receptor subtype binding
Clean Peptide's Melanotan II is sold as a 10 mg lyophilised vial for laboratory research only. PubChem CID 92432.
Explore Melanotan IIAlpha-MSH(4-10)Nle4, D-Phe7, Asp-Lys lactam ringMelanotan II (amide) / PT-141 (acid)
Both are cyclic analogues of the same alpha-MSH fragment; they differ only in the C-terminal group
Key Differences Between PT-141 and Melanotan II
| Key differences | PT-141 | Melanotan II |
|---|---|---|
| C-terminus | Free carboxylic acid (-OH). |
Amide (-NH2). |
| Formula and weight | C50H68N14O10, 1025.2 g/mol. |
C50H69N15O9, 1024.2 g/mol. One more N and H, one fewer O. |
| Names | PT-141, PT 141, PT141, bremelanotide (INN). |
Melanotan II, Melanotan 2, MT2, MT-II, MTII. |
| Registry numbers | CAS 189691-06-3; PubChem CID 9941379. |
CAS 121062-08-6; PubChem CID 92432. |
| Origin | Developed by Palatin Technologies from Melanotan II. |
Designed at the University of Arizona in the late 1980s. |
| Form sold here | Solution: 20 mg in a 20 mL spray bottle. |
Lyophilised powder: 10 mg vial. |
| Certificate on file (October 2026) | HYTE Research Division CLP#00003, lot 202609PTSP20: identity PT-141 confirmed (HPLC-DAD); quantity 1.31 mg/mL (curve assay, spec not less than 90% of label claim); pass. No purity or contaminant tests. |
ILS Laboratories COA-2026-BXNM7U, lot ACE-1234324: identity Melanotan II confirmed (HPLC-RTM); purity 99.82%; content 10.66 mg; fentanyl, heavy metals not detected; sterility no growth; endotoxin 0.058 EU/mL; pass. |
Where each one comes from
- PT-141
- Alpha-MSH
- Melanotan II (Arizona, amide)
- PT-141, free acid (Palatin)
- Melanotan II
- Alpha-MSH(4-10)
- Cyclic lactam analogues (1989)
- Melanotan II, amide
PT-141 vs Melanotan II: Which Is Better?
There is no basis for ranking them. They are two defined molecules that differ by one terminal group, and each is the right reference material only for work that names it.
What does differ in practice is the form and the certificate: here Melanotan II is a powder vial with purity, content and a contaminant panel, and PT-141 is a solution with identity and concentration.
Does the work call for the C-terminal amide (Melanotan II) or the free acid (PT-141), and as a dry powder or a ready-made solution?
Can a Certificate Tell PT-141 and Melanotan II Apart?
Only through the reference it is compared with. Both certificates confirm identity by HPLC against a reference standard for the named compound: retention-time match at ILS for Melanotan II, HPLC-DAD at HYTE for PT-141. Neither reports a measured mass, which is the measurement that would show the 1 g/mol difference directly.
So the name on the identity line is what ties each certificate to its molecule: "Melanotan II, Confirmed" and "PT-141 confirmed". Retention times from two laboratories' methods cannot be compared with each other; the PT-141 run's main peak at 6.643 minutes says nothing about where Melanotan II would elute on ILS's system.
Our Melanotan II COA guide reads that certificate line by line, and the nasal spray COA guide covers the PT-141 certificate alongside the other four spray certificates.
There Isn’t One Universal “Winner”
PT-141
Free-acid analogue
1025.2 g/mol • 20 mg in 20 mL solution
Melanotan II
Amide parent
1024.2 g/mol • 10 mg powder vial
Compare the Research. Verify the Material.
Clean Peptide stocks Melanotan II as a 10 mg lyophilised vial with an ILS Laboratories full-panel certificate, and PT-141 as 20 mg in a 20 mL spray bottle with a HYTE Research Division identity and quantity certificate.
Each lot's certificate is on the product page and in the COA library.
Research use only
Identity
confirmed- Lot
certificate
Research use only- Identity
confirmed - Lot
certificate
Question
Frequently Asked
What is the difference between PT-141 and Melanotan II?
Only the C-terminus. Both are Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]; Melanotan II ends in an amide (C50H69N15O9, 1024.2 g/mol) and PT-141 in a free carboxylic acid (C50H68N14O10, 1025.2 g/mol).
Is PT-141 the same as Melanotan II?
No. They share the same cyclic sequence but are two distinct molecules with different C-terminal groups, formulas, CAS numbers (189691-06-3 and 121062-08-6) and PubChem records.
Is PT-141 the same as bremelanotide?
Yes. PT-141 is the development code and bremelanotide the nonproprietary name for the same molecule.
Where does PT-141 come from?
Palatin Technologies developed PT-141 from Melanotan II, which was designed at the University of Arizona in the late 1980s as one of a series of cyclic lactam analogues of alpha-MSH.
Can a COA tell PT-141 and Melanotan II apart?
Through the named reference standard. Both certificates confirm identity by HPLC against a reference for the named compound; neither reports a measured mass, which would show the 1 g/mol difference directly.
What do the PT-141 and Melanotan II certificates show?
October 2026: PT-141 spray lot 202609PTSP20 (HYTE CLP#00003), PT-141 confirmed by HPLC-DAD and 1.31 mg/mL measured. Melanotan II 10 mg lot ACE-1234324 (ILS COA-2026-BXNM7U), 99.82% purity, 10.66 mg and identity confirmed by retention time.
Research Peptides. Documented by Batch.
Every size in the catalogue ships against the certificate issued for its own lot.
For laboratory research use only. Not for human or veterinary use.
References
Identity data come from PubChem (CID 9941379 for PT-141, CID 92432 for Melanotan II), as listed on our product pages. Study descriptions follow the PubMed abstracts.
- Al-Obeidi F, et al. Potent and prolonged acting cyclic lactam analogues of alpha-melanotropin: design based on molecular dynamics Journal of Medicinal Chemistry, 1989. Design of the cyclic lactam series that includes Melanotan II.
- Schiöth HB, et al. Selectivity of cyclic [D-Nal7] and [D-Phe7] substituted MSH analogues for the melanocortin receptor subtypes Peptides, 1997. Binding of Melanotan II at human MC1, MC3, MC4 and MC5 receptors.
- Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization Peptides, 2006. History of the Arizona programme; describes PT-141 as a Melanotan II analogue.
