Melanotan I and Melanotan II sound almost identical and are endlessly mixed up — but they're two distinct peptides studied through the melanocortin system, and they behave quite differently. Here's a clear side-by-side.

What each one is

Melanotan I (also called afamelanotide) is a linear synthetic analogue of α-MSH (alpha-melanocyte-stimulating hormone). It's relatively selective in which melanocortin receptors it engages.

Melanotan II is a shorter, cyclic analogue. The key difference is that it's less selective — it acts across a broader range of melanocortin receptors, which is exactly why it's studied in more research contexts than Melanotan I.

The key difference: selectivity

This is the heart of the comparison. Both work on the melanocortin system, but:

  • Melanotan I is more receptor-selective — research around it tends to be narrower and focused on pigmentation pathways.
  • Melanotan II is broader-acting — because it engages multiple melanocortin receptors (including MC4), it appears across a wider set of research fields.

Melanotan II is also closely related to PT-141 (bremelanotide), which is actually a metabolite of Melanotan II that acts more specifically on the MC4 receptor — we cover that pairing in Melanotan II vs PT-141.

Quick comparison

  • System: both are melanocortin (α-MSH) analogues
  • Structure: Melanotan I = linear; Melanotan II = shorter, cyclic
  • Receptor action: Melanotan I = more selective; Melanotan II = broader, multi-receptor
  • Research breadth: Melanotan I narrower (pigmentation focus); Melanotan II wider
  • Related compound: PT-141 is a more MC4-specific metabolite of Melanotan II
  • Handling: both are lyophilised powders — store cold, reconstitute with bacteriostatic water (use the calculator for volumes)

Sourcing in Australia

We hold Melanotan II in Australian stock, independently batch-tested with a published Certificate of Analysis. Because the two are so easily confused, verified identity on the vial is what tells them apart in practice — the CoA Library has the actual lab results before you order.

Shop melanocortin research peptides

All products are supplied strictly for laboratory and in-vitro research use only. Not for human or veterinary consumption. This article describes fields of scientific research and is not medical advice or a claim about effects in humans.