Melanotan I vs Melanotan II (MT-2): A Research Comparison
Melanotan I and Melanotan II are both synthetic analogs of alpha-MSH studied within melanogenesis and melanocortin-receptor research, differing mainly in structure. Melanotan I is a linear 13-residue analog, while Melanotan II (MT-2) is a shorter cyclic heptapeptide. They also differ sharply in regulatory status. Both are for research use only and are not approved for human use in this form.
Mechanism contrast: linear vs cyclic backbone
Both compounds are synthetic analogs of alpha-melanocyte-stimulating hormone (alpha-MSH) studied as agonists of the melanocortin receptor family, but they differ in backbone architecture. Melanotan I (afamelanotide) is a linear 13-residue analog that retains much of the native alpha-MSH sequence and is referenced in research mainly within pigmentation and melanocortin-1-receptor contexts.
Melanotan II (MT-2) is a truncated, cyclic, amidated heptapeptide referenced in research for agonist activity across additional melanocortin receptor subtypes. The linear-versus-cyclic backbone and the associated receptor-subtype profiles are the mechanistic axes on which the two are compared, and they also give the pair very different molecular weights (near 1646.9 g/mol for Melanotan I versus near 1024.2 g/mol for MT-2).
Research context and regulatory status
The two differ sharply in regulatory status, which is a matter of public record. The linear analog, as afamelanotide, is an approved drug: it is marketed as SCENESSE and has been authorized by the FDA and EMA for the rare light-sensitivity condition erythropoietic protoporphyria. Melanotan II has no such approval.
Melanotan II's closest approved relative is the structurally similar melanocortin agonist bremelanotide (PT-141), which is marketed as Vyleesi. Stating these approvals reports the molecules' verifiable regulatory status; it is not a claim that Pinnacle's research materials are drugs or are intended for human use. Both Melanotan I and Melanotan II are supplied here strictly for laboratory research.
Handling parity and the weight difference
Handling is the same for both: lyophilized powder stored at -20°C protected from light, reconstituted with bacteriostatic water added gently against the vial wall, then refrigerated with freeze-thaw cycles minimized. The practical difference at the bench is mass, not method.
Melanotan I is the larger molecule (near 1646.9 g/mol) while the cyclic Melanotan II is markedly smaller (near 1024.2 g/mol), so equal vial masses correspond to different molar quantities, a distinction to reconcile against each lot-matched Certificate of Analysis when preparing molar-based research solutions. Both COAs report HPLC purity and mass-spectrometry identity; confirm salt form there as well.
How researchers choose, and the PT-141 relationship
Choice tracks the receptor question. Pigmentation and MC1-focused melanogenesis research more often references the linear Melanotan I, while research reaching into the broader melanocortin receptor family more often references the cyclic Melanotan II.
The group extends naturally to PT-141 (bremelanotide), the free-acid analog of Melanotan II that differs only at the C-terminus (free acid versus amide). Because these three sit on a shared structural spine, they form a compact structure-activity set for melanocortin-receptor pharmacology: linear versus cyclic between the two Melanotans, and amide versus free acid between Melanotan II and PT-141. All three are supplied as lyophilized powder for research use.
All products are intended strictly for in-vitro laboratory research and development use only. Not for human or veterinary use, not a drug, food, or cosmetic, and not intended to diagnose, treat, cure, or prevent any disease.