Melanotan I vs Melanotan II: A Research Comparison of α-MSH Analogs
Side-by-side overview of Melanotan I (MT-1) and Melanotan II (MT-2) — two synthetic α-MSH analogs studied in pigmentation, melanocortin-receptor, and dermal-biology research.
For in-vitro and laboratory research only. The molecules below are research-grade peptides; nothing constitutes guidance for human use, including any cosmetic or tanning context.
Melanotan I and Melanotan II are two synthetic analogs of alpha-melanocyte-stimulating hormone (α-MSH), the 13-amino-acid POMC-derived peptide that activates melanocortin receptors. The two are often grouped together — and often confused — in the research-peptide market. They are structurally and pharmacologically distinct. Both are available lyophilized as MT-1 10mg and MT-2 10mg.
What each molecule is
Melanotan I (Afamelanotide)
Melanotan I is a linear 13-amino-acid α-MSH analog with two substitutions (Nle⁴, D-Phe⁷). It is highly selective for the melanocortin-1 receptor (MC1R) — the receptor primarily expressed on melanocytes. The clinical compound afamelanotide is the same molecule and has been studied in published clinical literature for erythropoietic protoporphyria.
Melanotan II
Melanotan II is a cyclic 7-amino-acid α-MSH analog. The cyclization and shorter sequence give it a broader melanocortin-receptor profile — in particular, significant activity at MC3R and MC4R, the central-nervous-system melanocortin receptors. The MC4R activity is responsible for the appetite- and libido-related effects observed in animal-model literature, and is the structural rationale for the related research compound PT-141.
Side-by-side comparison
| Attribute | Melanotan I | Melanotan II |
|---|---|---|
| Structure | Linear, 13 amino acids | Cyclic, 7 amino acids |
| Approx. MW | ~1646 Da | ~1024 Da |
| Receptor selectivity | MC1R-selective | MC1R, MC3R, MC4R (broad) |
| Primary research interest | Pigmentation, photoprotection models | Pigmentation + appetite/libido pathways |
| Clinical analog | Afamelanotide | None approved |
The PT-141 connection
PT-141 (bremelanotide) is structurally a metabolite-stabilized analog of Melanotan II focused on MC4R agonism without the MC1R pigmentation activity. See our PT-141 research overview for the bremelanotide story; PT-141 10mg is available as a research product.
Handling and storage
Both peptides ship lyophilized and follow standard storage protocol — sealed at −20°C protected from light. See our peptide storage guide for shelf life by storage condition. Both are reconstituted in bacteriostatic water for standard research workflows.
What to verify on the COA
- Sequence and structure — for MT-2 in particular, confirm the cyclic structure and 7-residue length.
- Purity ≥98% by HPLC.
- Mass spec match for the expected MW (very different between MT-1 and MT-2 — an obvious sanity check).
See how to read a peptide COA.
Reminder: All material above is summarized from preclinical research literature. Products are not intended for human consumption.