Melanotan-1 vs melanotan-2: selectivity is the difference
Melanotan-1 is comparatively selective for the melanocortin-1 receptor. Melanotan-2 is a cyclic lactam analogue that retains affinity across several melanocortin receptors, including MC3R and MC4R. That difference decides which one a design can attribute an effect to.
| Melanotan-1 | Melanotan-2 | |
|---|---|---|
| Receptor preference | MC1R-selective | MC1R, MC3R, MC4R, MC5R |
| Structure | Linear 13-residue analogue | Cyclic lactam heptapeptide |
| Length | 13 residues | 7 residues |
| Molecular weight | 1646.8 g/mol | 1024.2 g/mol |
| CAS | 75921-69-6 | 121062-08-6 |
| Best suited to | MC1R and pigmentation assays | Receptor-selectivity mapping |
Why does selectivity decide the experiment?
An effect observed with melanotan-2 could come from any of four receptors without further controls. The same effect with melanotan-1 narrows to MC1R. Non-selectivity is useful for mapping and a liability for attribution.
How does PT-141 relate to these?
PT-141 is a metabolite of melanotan-2 with the C-terminal amide replaced, which shifts activity away from MC1R toward MC3R and MC4R. It is listed separately in this catalogue.
Are either the same as alpha-MSH?
Neither. Both are analogues of alpha-melanocyte-stimulating hormone carrying substitutions that resist degradation; the native hormone is a different molecule.
What do the current certificates show?
Pharmacology decides which compound answers the question; the certificate decides what is actually in the vial. These are the current lots for each, read from the certificate library:
| Compound | Lot | Identity | Purity | Content | Issued |
|---|---|---|---|---|---|
| Melanotan-1 | MT110-0318 | MALDI-MS | 99.8% | 10.78 mg vs 10 mg label | Apr 3, 2026 |
| Melanotan-2 | No certificate published for the current lot yet. | ||||
Purity on both lines is area percent by RP-HPLC at 214 nm, which the area-percent post explains is a ratio of peak areas and not a weight, so the two figures are comparable only because the method is the same. Content is the measured mass against the label, and the lot-to-lot post is the case for using it rather than the label in any calculation. All 114 certificates read together are in the certificate dataset.
Common questions
Which is the cyclic one?
Melanotan-2. The cyclic lactam structure is what retains affinity across the melanocortin receptor family.
Does melanotan-1 have another name?
Afamelanotide. Both names refer to the same MC1R-selective analogue.
Where to go next
- Melanotan-1 research guide · Melanotan-1 product page
- Melanotan-2 research guide · Melanotan-2 product page
For laboratory research use only. Clinical trial results are cited as context and do not describe use of the material sold here.