Melanotan 1 vs. Melanotan 2: What's the Difference?

Both Melanotan 1 (afamelanotide) and Melanotan 2 are synthetic analogues of α-MSH, but they were developed at different times, have different molecular structures, and interact with melanocortin receptors differently — which is why researchers treat them as distinct compounds rather than interchangeable versions of the same peptide.

Melanotan 1

Melanotan 1 is a linear peptide, structurally closer to the native α-MSH sequence, with high selectivity for the MC1R receptor. It was the first of the two to be synthesised, at the University of Arizona in 1980, and its receptor selectivity has made it the more extensively studied of the pair in a clinical context — it's the basis of afamelanotide (Scenesse), approved by the EMA in 2014 for a specific rare skin condition.

Melanotan 2

Melanotan 2 is a cyclic analogue, synthesised over a decade later. Its cyclic (lactam-bridged) structure gives it broader receptor activity, engaging MC1R, MC3R, MC4R, and MC5R rather than MC1R alone. That broader receptor profile is why Melanotan 2 has been used more widely as a general-purpose tool in melanocortin pathway research, including studies touching on energy homeostasis via MC4R.

Key Differences at a Glance

• Structure: Melanotan 1 is linear; Melanotan 2 is cyclic.
• Receptor selectivity: Melanotan 1 is MC1R-selective; Melanotan 2 engages multiple melanocortin receptors.
• Molecular weight: Melanotan 1 ≈ 1647.8 Da; Melanotan 2 ≈ 1024.2 Da.
• Regulatory status: Melanotan 1's analogue afamelanotide has an approved clinical indication in the EU; Melanotan 2 does not have an approved therapeutic use anywhere.
• Stability: both incorporate D-amino acid substitutions that improve resistance to enzymatic degradation relative to native α-MSH, aiding reproducibility in multi-day in vitro assays.

For the underlying receptor biology, see how melanocortin receptor agonists work, or view full technical specifications on our Science page.