Guide
Melanotan 1 vs melanotan 2 vs PT-141
Three melanocortin peptides: one linear, one cyclic, and one derived from the cyclic form. Sequences, masses and receptor targets.
Published September 4, 2026
Three melanocortin peptides, related by chemistry rather than by name.
| Peptide | Vial sizes | From |
|---|---|---|
| Melanotan 1 | Single size | $59.99 CAD |
| Melanotan 2 | 10mg | $49.99 CAD |
| PT-141 | 10mg | $49.99 CAD |
Free shipping across Canada. Every vial ships with a QR code linking to its own batch lab report. See all peptides
Linear, then cyclic, then a metabolite
Alpha-melanocyte-stimulating hormone is the natural starting point. Melanotan 1 is a linear analog of it, 13 residues, also called afamelanotide.
Melanotan 2 took a different route: cut the sequence down and close it into a ring. Cyclising a peptide makes it far harder for peptidases to attack, which is why the shorter molecule is the more stable one. It also broadened its activity across melanocortin receptor subtypes rather than narrowing it.
PT-141 is what you get when melanotan 2's C-terminal amide becomes a carboxylic acid. It is a metabolite of melanotan 2, not a redesign, and it is studied for a different receptor profile. Its other name is bremelanotide.
The numbers
| Structure | Formula | Molecular weight | CAS | |
|---|---|---|---|---|
| Melanotan 1 | Linear, 13 residues | C78H111N21O19 | 1646.85 g/mol | 75921-69-6 |
| Melanotan 2 | Cyclic, 7 residues | C50H69N15O9 | 1024.18 g/mol | 121062-08-6 |
| PT-141 | Cyclic, 7 residues | C50H68N14O10 | 1025.16 g/mol | 189691-06-3 |
Melanotan 2 and PT-141 differ by one nitrogen and one oxygen, which is a hair under one gram per mole. If a report's observed mass is printed to two decimal places you can still separate them, but this is the one pair in the catalog where you should read the formula on the certificate as well as the mass. How to read a peptide lab report covers what else the certificate should show.
Reconstitution
All three ship as 10 mg vials.
| Vial | 1 mL | 2 mL | 3 mL | 5 mL |
|---|---|---|---|---|
| 10 mg | 10 mg/mL9.76 mM | 5 mg/mL4.88 mM | 3.33 mg/mL3.25 mM | 2 mg/mL1.95 mM |
Melanotan 2 vial sizes we sell, at four diluent volumes. Molarity uses 1024.18 g/mol. Other volumes
Melanotan 1 is 60% heavier, so the same 10 mg is about 6 micromoles rather than about 10. Its calculator page has the molecular weight preset.
Quick version
Linear 13-mer is melanotan 1. Cyclic 7-mer is melanotan 2. Its acid metabolite is PT-141. Masses: 1,647, 1,024 and 1,025.
For research use only. Not for human or animal consumption.
Frequently asked questions
What is the difference between melanotan 1 and melanotan 2?+
Shape and size. Melanotan 1 is a linear 13-residue analog of alpha-MSH at 1,646.85 g/mol. Melanotan 2 is a cyclic seven-residue peptide at 1,024.18. Cyclising the molecule made it shorter, more stable and less selective across melanocortin receptors.
Is PT-141 the same as melanotan 2?+
No, but it comes from it. PT-141, also called bremelanotide, is a metabolite of melanotan 2 in which the terminal amide is replaced by a carboxylic acid. That single change adds about one gram per mole and shifts its receptor profile.
What is afamelanotide?+
Another name for melanotan 1. The two names describe the same 13-residue linear peptide.
How do I tell PT-141 from melanotan 2 on a report?+
By about one gram per mole: 1,025.16 against 1,024.18. That is a small gap, so read the observed mass to two decimal places and check the formula as well. PT-141 has one fewer nitrogen and one more oxygen.
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