Source comparison
Melanotan I vs Melanotan II vs PT-141: Structural Differences Drive Receptor Selectivity
Melanotan I (afamelanotide, commercially known as Scenesse) is a linear 13-amino-acid peptide nearly identical to endogenous α-MSH, with a single amino acid substitution (norleucine replacing methionine at position 4) to increase stability. It binds MC1R with
This comparison does not assign a generated winner or score.
- Melanotan I (afamelanotide, commercially known as Scenesse) is a linear 13-amino-acid peptide nearly identical to endogenous α-MSH, with a single amino acid substitution (norleucine replacing methionine at position 4) to increase stability. It binds MC1R with high affinity and MC4R/MC5R with moderate affinity, producing dose-dependent skin darkening with minimal central effects—hence its FDA approval for erythropoietic protoporphyria, where increased eumelanin provides photoprotection. Melanotan II is a cyclized 7-amino-acid analog with a lactam bridge between positions 4 and 10, creating a constrained structure that binds all melanocortin receptors except MC2R. This non-selectivity is why melanotan II produces tanning, appetite suppression, spontaneous erections, and nausea simultaneously—it's hitting multiple receptor subtypes at once.
- PT-141 (bremelanotide) is a des-acetyl modification of melanotan II, removing the N-terminal acetyl group to shift receptor affinity away from MC1R toward MC3R and MC4R. The result: preserved central nervous system effects (arousal, appetite modulation) with dramatically reduced melanogenesis. Clinical trials of PT-141 in women with hypoactive sexual desire disorder showed statistically significant increases in satisfying sexual events without the skin darkening that plagued melanotan II trials. The modification doesn't eliminate MC1R binding entirely—PT-141 still produces mild tanning at high doses—but the therapeutic index is far better. We've found that researchers choosing between these compounds need to define their primary outcome first: if pigmentation is the goal, melanotan I or II. If central appetite or arousal modulation without cosmetic side effects, PT-141.