Melanotan I and melanotan II are two different synthetic analogues of alpha-melanocyte-stimulating hormone (alpha-MSH). They are often confused with each other, and they differ in structure, size and receptor selectivity. This guide sets out the differences, how each is verified analytically, and where each stands with regulators.
- Melanotan I
- [Nle4, D-Phe7]-alpha-MSH, 13 amino acids, approx. 1,647 Da (also called afamelanotide)
- Melanotan II
- Cyclic heptapeptide lactam analogue, approx. 1,024 Da
- Receptors
- Melanocortin receptors; melanotan II is less selective than melanotan I
- Supplied as
- Lyophilised vials
- Purity method
- RP-HPLC; identity by mass spectrometry
Two different molecules
Melanotan I is a linear, 13-residue analogue of alpha-MSH in which two residues are swapped to make it more resistant to breakdown. Melanotan II is a much shorter, cyclic analogue built around a lactam bridge. They have different masses, so a mass-spectrometry result immediately tells you which one a vial contains.
What the research literature studies
Melanocortin peptides are used in laboratory work on the five melanocortin receptors (MC1R to MC5R) and the signalling they trigger in cell-based assays. Melanotan II binds several of these receptors, while melanotan I is more selective for MC1R. These are receptor-pharmacology findings and not claims about effects in people.
Identity and purity: what a good CoA shows
Because the two compounds are so often confused, the observed mass on the CoA matters more than usual: roughly 1,647 Da for melanotan I and roughly 1,024 Da for melanotan II. A CoA that gives purity but not mass cannot tell you which molecule you have.
- RP-HPLC purity with the chromatogram attached
- Observed intact mass that matches the compound you ordered
- A batch reference that matches your vial label
Handling and storage
Keep sealed lyophilised vials cold, dry and out of light, and avoid repeated freeze-thaw cycles of any solution. The general principles in our cold-chain and shelf-life guides apply.
Regulatory status
Afamelanotide (melanotan I) is licensed in the UK and EU only as a prescription implant for one rare medical condition; that regulated medicine is a different product from research material. Melanotan II is not a licensed medicine anywhere in the UK or EU, and the MHRA has publicly warned consumers against unlicensed melanotan products. Nordapep supplies both strictly for in vitro laboratory research, and they must not be used in people or animals.
Questions researchers ask
What is the difference between melanotan I and melanotan II?
They are different molecules. Melanotan I is a linear 13-amino-acid analogue of alpha-MSH (approx. 1,647 Da); melanotan II is a smaller cyclic analogue (approx. 1,024 Da) that acts on more melanocortin receptors.
How can I tell which one is in a vial?
By intact mass. Mass spectrometry will show roughly 1,647 Da for melanotan I and roughly 1,024 Da for melanotan II, so ask for the observed mass on the CoA.
Is melanotan a licensed medicine?
Afamelanotide, a form of melanotan I, is licensed only as a prescription implant for a specific rare condition. Melanotan II is not licensed. Research material is neither and is not for use in people or animals.
