Melanotan I vs Melanotan II
Melanotan I (Melanocortin receptor agonist) and Melanotan II (Melanocortin receptor agonist) are documented as co-studied in the PeptiDex library. This page puts the two entries side by side on class, molecular weight, half-life, origin, mechanism and studied research areas — every value taken from the entry it belongs to.
Why these two are co-studied
Cross-referenced for research context — not a usage or combination recommendation.
At a glance
| Attribute | Melanotan I | Melanotan II |
|---|---|---|
| Compound class | Melanocortin receptor agonist | Melanocortin receptor agonist |
| Research category | Cosmetic & Dermal | Cosmetic & Dermal |
| Length (amino acids) | 13 amino acids | 7 amino acids |
| Molecular weight | ~1646 g/mol | ~1024 g/mol |
| Half-life | ~0.8-1.7 h (free peptide, SC beta-phase); ~15 h apparent for the Scenesse implant | ~30-60 minutes (plasma, subcutaneous) |
| Origin | Melanotan I is a synthetic analog of alpha-melanocyte-stimulating hormone (alpha-MSH), developed at the University of Arizona in the 1980s. Its clinically developed form, afamelanotide, is marketed as Scenesse. | Melanotan II is a synthetic cyclic analog of alpha-melanocyte-stimulating hormone (alpha-MSH), developed from melanocortin research at the University of Arizona. It is a distinct, non-selective compound from the linear Melanotan I. |
“Not documented” means the PeptiDex entry records no value for that field. Nothing on this page is estimated, and no figure is carried over from one compound to the other.
How Melanotan I works
Melanotan I is a superpotent, more metabolically stable analog of alpha-MSH that acts as an agonist at melanocortin receptors, with high activity at MC1R. Activation of MC1R on melanocytes stimulates the cAMP pathway, increasing production of eumelanin (melanogenesis) and skin pigmentation. Compared with native alpha-MSH, the substitutions (including Nle and D-Phe) confer greater resistance to enzymatic degradation and longer duration of action.
How Melanotan II works
Melanotan II is a cyclic heptapeptide that acts as a non-selective agonist across melanocortin receptors, including MC1R and MC4R. MC1R agonism on melanocytes stimulates melanogenesis and pigmentation, while MC4R agonism in the central nervous system is associated with effects on sexual arousal, which is the pharmacological basis linking it to the MC4R agonist bremelanotide (PT-141). Its cyclic, constrained structure contributes to potency and metabolic stability.
Mechanistic descriptions reflect published research-literature understanding and are quoted from each compound's own entry. Much peptide research is preclinical (in-vitro or animal-model); mechanism in humans may differ and is not established for many compounds.
Where each one appears in the literature
The research contexts each entry documents. Listing a research area is not a claim of efficacy or a therapeutic indication, and the two lists are not scored against each other.
Melanotan I
Melanotan II
What sets each apart
Melanotan I
Unlike Melanotan II, Melanotan I (afamelanotide) is a linear alpha-MSH analog with an approved clinical form (Scenesse) and comparatively MC1R-focused pigmentation activity.
Melanotan II
Melanotan II is a cyclic, non-selective melanocortin agonist (MC1R and MC4R), distinguishing it from the linear, more MC1R-focused Melanotan I and from the MC4R-selective PT-141.
Frequently asked questions
How does Melanotan I differ from Melanotan II?
Melanotan I is a longer, linear 13-residue alpha-MSH analog that is relatively MC1R-focused, while Melanotan II is a smaller cyclic heptapeptide that is broadly non-selective across melanocortin receptors. The narrower activity of Melanotan I is associated with fewer of the off-target effects (like libido changes) seen with MT-II.
What is Melanotan I?
Melanotan I is the peptide Nle4-D-Phe7-alpha-MSH, a 13-amino-acid linear analog of alpha-melanocyte-stimulating hormone. It is the same molecule as afamelanotide, and it acts as a melanocortin-1-receptor agonist that stimulates melanin production.
How does Melanotan I relate to afamelanotide and Scenesse?
They are the same active molecule. Afamelanotide is the pharmaceutical name, and Scenesse is the FDA-approved controlled-release subcutaneous implant form (approved in 2019) used to increase pain-free light exposure in adults with erythropoietic protoporphyria (EPP). The research-peptide term 'Melanotan I' refers to the same compound outside that approved implant.
What is Melanotan II?
Melanotan II (MT-II) is a synthetic cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone (alpha-MSH). It is a non-selective melanocortin receptor agonist studied in models of melanogenesis (pigmentation) and, via MC4R activity, sexual-response pathways. It is not an approved drug.
How does Melanotan II differ from Melanotan I?
Melanotan I (afamelanotide) is a linear 13-amino-acid alpha-MSH analog and is relatively MC1R-focused, while Melanotan II is a smaller cyclic heptapeptide that is broadly non-selective across melanocortin receptors. The broader receptor activity of MT-II is associated with additional effects such as libido changes and nausea seen in its research literature.
What is the reported half-life of Melanotan II?
Reported plasma half-life is short, on the order of roughly 30 minutes to about 1 hour after subcutaneous administration (some sources cite ~33 minutes). Importantly, pigmentation effects persist for days to weeks because melanocytes are stimulated to produce melanin, so the short plasma half-life does not reflect the duration of the observable effect.
Answers are the ones published on each compound's own PeptiDex entry. They are educational summaries of research-literature context and are not medical advice.