Melanotan I (MT-1) and Melanotan II (MT-2) are both synthetic analogues of the endogenous hormone α-MSH (alpha-melanocyte-stimulating hormone) and are often confused or treated as interchangeable in a research context. Structurally and pharmacologically, however, they differ considerably – with direct consequences for receptor selectivity and the activity profile being studied. This article compares the two on the basis of published studies.
Structure compared
Melanotan I (scientific name: [Nle4, D-Phe7]-α-MSH) is a linear 13-amino-acid peptide – essentially the complete α-MSH sequence with two stabilising substitutions. Under the international non-proprietary name afamelanotide, exactly this molecule has been approved as a medicinal product in the US since 2019 (see approval status below).
Melanotan II, by contrast, is a cyclic heptapeptide – a heavily shortened version of the α-MSH core sequence closed into a ring by a lactam bridge. This cyclisation significantly increases receptor binding affinity but also fundamentally changes receptor selectivity.
Mechanism of action compared
Both peptides activate melanocortin receptors – the decisive difference lies in receptor selectivity:
- Melanotan I is described in research as a largely selective MC1R agonist. MC1R is located on melanocytes, where it controls melanin production. As MT-1 barely activates other melanocortin receptors (in particular MC3R/MC4R in the central nervous system), it is studied primarily in the context of pigmentation research.
- Melanotan II, on the other hand, non-selectively activates several melanocortin receptor subtypes (MC1R, MC3R, MC4R, MC5R). The additional MC4R activation – a receptor that regulates appetite and sexual behaviour, among other things, in the hypothalamus – explains why side effects beyond pigmentation were systematically observed in studies on MT-2 (see below).
State of research
For both molecules there are phase I studies from the 1990s by the research group around Dorr, Hadley and Levine (University of Arizona):
- For MT-1, Ugwu et al. (1997) investigated pharmacokinetics and pigmentation effect in three male volunteers via intravenous, oral and subcutaneous administration. Only subcutaneous and intravenous administration produced measurable drug levels (oral bioavailability was not detectable); visible tanning of the forehead, arms and neck occurred and was still detectable three weeks after the end of administration.
- For MT-2, Dorr et al. (1996) documented in a placebo-controlled pilot study with three volunteers not only dose-dependent pigmentation but also dose-limiting side effects: nausea, flushing and spontaneous erections – effects the authors attributed to the additional MC4R activation and which were not described to this extent for MT-1 in comparable studies.
Approval status
Here the two molecules differ fundamentally: Melanotan I has been approved by the US FDA as a medicinal product under the name afamelanotide (Scenesse®) since October 2019 – not for cosmetic tanning, however, but for the treatment of erythropoietic protoporphyria (EPP), a rare metabolic disorder with extreme sensitivity of the skin to light. Melanotan II, by contrast, has no marketing authorisation in the US, the EU or other major regulatory regions. AlpenPeptides offers both molecules exclusively as research peptides for scientific research – not as medicinal products and not for use in humans.
Direct comparison
| Melanotan I | Melanotan II | |
|---|---|---|
| Structure | linear, 13 amino acids | cyclic, 7 amino acids |
| Receptor profile | largely MC1R-selective | non-selective: MC1R, MC3R, MC4R, MC5R |
| Key study | Ugwu et al., 1997 (Biopharm. Drug Dispos.) | Dorr et al., 1996 (Life Sciences) |
| Side effects observed (studies) | minor | nausea, flushing, spontaneous erections (dose-dependent) |
| Approval status | FDA-approved as afamelanotide/Scenesse® (EPP) | no marketing authorisation |
Conclusion
Despite their similar names, Melanotan I and Melanotan II are pharmacologically clearly distinct molecules: MT-1 as a largely MC1R-selective linear peptide that has already been approved as a medicinal product for a specific indication, MT-2 as a non-selective cyclic multi-receptor agonist with a side-effect profile documented more broadly in studies. Which molecule is relevant for a particular research question depends on the receptor mechanism being studied.
Both research peptides are available in our shop – lab-tested and COA-certified: Melanotan I and Melanotan II.
Sources & further studies
- Dorr RT, Lines R, Levine N, et al. (1996): Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sciences, 58(20):1777-1784. PMID: 8637402
- Ugwu SO, Blanchard J, Dorr RT, et al. (1997): Skin pigmentation and pharmacokinetics of melanotan-I in humans. Biopharmaceutics & Drug Disposition, 18(3):259-269. PMID: 9113347
- U.S. Food and Drug Administration (2019): FDA approval of afamelanotide (Scenesse) for erythropoietic protoporphyria. FDA approval letter (accessdata.fda.gov)
Note: this article is for information and research purposes only and does not constitute medical advice. Melanotan I and Melanotan II for research are not intended for human consumption or for use in humans. The FDA approval of afamelanotide (Scenesse®) mentioned above refers to an approved, physician-administered medicinal product and not to the research peptides offered in our shop.