Home Research library Melanotan I vs Melanotan II
Comparison
Melanotan I vs Melanotan II
Melanotan I and Melanotan II are separate research compounds. This page sets what our catalogue and the laboratory certificates state about each one side by side: identifiers, formula, molecular weight, chain length, form and storage. It describes the materials, not what they do, and carries no use guidance.
Specification, side by side
| Melanotan I | Melanotan II | |
|---|---|---|
| Also known as | Afamelanotide | MT-2 |
| Catalogue shelf | Research peptides | Research peptides |
| CAS number | 75921-69-6 | 121062-08-6 |
| Molecular formula | C78H111N21O19 | C50H69N15O9 |
| Molecular weight | 1,646.87 g/mol | 1,024.2 g/mol |
| Chain length | 13 residues | 7 residues |
| Sequence | Ac-SYSNle-EHdFRWGKPV-NH2 | Not stated by our supplier |
| Form as supplied | Lyophilized powder | Lyophilized powder |
| Storage | -20 °C, desiccated | -20 °C, desiccated, protect from light |
| Sizes stocked | 10 mg | 10 mg |
| Current certificates | 10 mg: 99.8%, lot MT110-0318 | None on file |
| PubChem record | CID 16197727 | CID 92432 |
Figures are the ones printed on each product page. Purity appears only where a current laboratory certificate supports it, and links to that certificate.
What differs
- Chain length: Melanotan I has 13 residues and Melanotan II has 7 residues.
- Molecular weight: Melanotan I is 1,646.87 g/mol and Melanotan II is 1,024.2 g/mol. Melanotan I is the largest of the two.
- Each has its own CAS registry number (Melanotan I: 75921-69-6 and Melanotan II: 121062-08-6), which is how a chemical supplier tells them apart on paper.
- Their molecular formulas differ: C78H111N21O19 for Melanotan I and C50H69N15O9 for Melanotan II.
What each one is
Melanotan I
The linear thirteen-residue analogue, as against the cyclic melanotan II a shelf over. Both carry a D-phenylalanine at position seven; this one has no lactam bridge, which makes it the easier synthesis and the cheaper vial. See Melanotan I.
Melanotan II
A cyclic lactam analogue of alpha-MSH, non-selective across MC1R, MC3R, MC4R and MC5R, though not at MC2R, which answers only to ACTH. Used to examine melanocortin receptor pharmacology, melanogenesis in melanocyte culture and central melanocortin signalling in rodent feeding studies. See Melanotan II.
Common questions
Are Melanotan I and Melanotan II the same compound?
No. They are separate compounds with separate CAS registry numbers: 75921-69-6 for Melanotan I and 121062-08-6 for Melanotan II. They are sold as separate items and certified separately.
Which is the larger molecule, Melanotan I or Melanotan II?
Melanotan I, at 1,646.87 g/mol. Melanotan II is 1,024.2 g/mol.
Is there a certificate of analysis for Melanotan I and Melanotan II?
Melanotan I has 1 current certificate in the testing library, each linked to the laboratory's own file. There is no current certificate on file for Melanotan II, so no purity figure is printed for it.
Does this page say what Melanotan I and Melanotan II are used for?
No. It compares the materials as chemicals: identifiers, formula, weight, chain length, form and storage. Everything here is sold for laboratory research use only, and the site publishes no use guidance.
Further reading
- Melanotan II, PT-141 and afamelanotide: one parent, three analoguesAfamelanotide, Melanotan II and bremelanotide all descend from the 13-residue hormone alpha-MSH. Two became approved drugs; Melanotan II never did. Structures, lineage, FDA's own words on MT-II, and status as of September 2026.
Other comparisons
For laboratory research use only. Not a drug, not a supplement, not for human or veterinary use.