Melanotan I (afamelanotide) is a synthetic 13-amino-acid linear analog of alpha-melanocyte-stimulating hormone (α-MSH), developed at the University of Arizona in the 1980s and one of the few compounds in research-vendor catalogues that has progressed to a registered human therapy in any major jurisdiction. This monograph lays out its chemical identity, melanocortin-receptor pharmacology, the published research record, and how it sits relative to the more widely-discussed Melanotan II.
Chemical identity and structure.
Melanotan I has the sequence Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH₂. It is a linear 13-mer modified at position 4 (norleucine in place of methionine, for oxidative stability) and at position 7 (D-phenylalanine in place of L-phenylalanine, for enzymatic-degradation resistance). The "afamelanotide" INN designates the same molecule. Molecular weight is 1646.8 g/mol. Unlike its more famous cyclic cousin Melanotan II, Melanotan I retains the full 13-residue α-MSH backbone and is considered the closer structural analog to native α-MSH.
Mechanism of action.
Melanotan I is a non-selective melanocortin receptor (MC-R) agonist with primary activity at MC1R, the receptor expressed on melanocytes and responsible for eumelanin synthesis. Through MC1R activation it stimulates cAMP signalling, tyrosinase expression, and the eumelanin/pheomelanin switch — the mechanism that drives the photoprotective effect characterised in published clinical research. It also has measurable affinity at MC3R, MC4R, and MC5R, though its therapeutic profile is dominated by MC1R activity. The MC4R component is the reason side-effects in published trials track CNS appetite and libido pathways.
Research applications and the evidence base.
Melanotan I has, unusually for this market, a substantive published human clinical record. It is registered under the brand name Scenesse for erythropoietic protoporphyria (EPP) in the EU (EMA, 2014) and the US (FDA, 2019), where it functions as a melanin-density-increasing therapy that reduces phototoxic reactions to visible light. Earlier-phase trials have been conducted in vitiligo, polymorphous light eruption, and solar urticaria. Research applications outside its registered indication include photoprotection modelling, MC1R signalling characterisation, and skin-pigmentation biology in preclinical models. Researchers should be aware that the registered Scenesse product is a slow-release implant, not the lyophilized injectable form sold in research-vendor catalogues — the pharmacokinetic profile is markedly different.
Research context.
Melanotan I and Melanotan II are frequently confused but pharmacologically distinct. Melanotan II is a shorter cyclic analog with much stronger MC4R activity (and consequently stronger CNS effects); Melanotan I is the longer linear molecule with cleaner MC1R selectivity and a well-defined registered therapeutic profile. Researchers studying photoprotection or MC1R isolated pharmacology typically work with Melanotan I; researchers studying broader melanocortin-system pharmacology (appetite, sexual-function pathways) typically work with Melanotan II.
Storage and handling.
Lyophilized vials should be kept refrigerated (2–8 °C) and protected from light. Melanotan I tolerates refrigerator-temperature storage reasonably well, but does not tolerate repeated freeze-thaw cycles. The lyophilized powder should appear white to off-white.
Quality and COA considerations.
A meaningful COA should confirm identity via mass spectrometry (1646.8 g/mol target), purity by HPLC (≥98% benchmark), and explicit disambiguation from Melanotan II — sequence-mislabelling between the two molecules is a known quality issue. Sterility and endotoxin testing should be reported for any vial intended for injection-model use.
Research-use note: This monograph is an educational summary of the published research literature on Melanotan I (afamelanotide). The registered human therapy (Scenesse) is approved only for erythropoietic protoporphyria; the lyophilized research-grade product is not approved for human use in any other indication or jurisdiction known to VialTalk. Nothing here is medical advice or a usage recommendation.