What it is
Melanotan II is an unlicensed synthetic peptide in the melanocortin family — a group of signalling molecules the body uses for pigmentation, appetite, inflammation and sexual arousal, among other things.
It works mainly by activating melanocortin 1 receptors on melanocytes, the pigment-producing cells in skin. PT-141 is the approved medicine from the same receptor family, and the contrast between the two is instructive. That drives eumelanin production and darkens the skin without any sun exposure. It is bought over the internet, most often as a tanning agent, and also used for its effect on arousal.
Why the side effects are the mechanism
Melanotan II does not select cleanly between melanocortin receptor subtypes, and those receptors are not confined to skin. They appear in the cardiovascular system, the kidneys, the adrenal axis and the pathways involved in erection.
So the reported problems are not random misfortune. They are the same mechanism acting where it was not wanted — a pattern that recurs whenever a signalling peptide is asked to act in one tissue only.
What has been documented
The case-report literature on this compound is unusually substantial. Published reports link melanotan II use to:
- Rhabdomyolysis — muscle breakdown, which can damage the kidneys
- Renal infarction and acute renal failure
- Priapism
- Exogenous hypercortisolism
One documented case describes a 39-year-old man who injected 6 mg subcutaneously — six times the commonly cited starting dose — to darken his skin in winter, and developed sympathomimetic symptoms, rhabdomyolysis and renal dysfunction.
The melanoma question
Case reports describe melanoma and dysplastic naevi in users. One describes a mucosal malignant melanoma of the anterior maxilla in a 22-year-old woman who had used a melanotan II nasal spray. Another describes multiple primary melanomas in situ in a patient with recent tanning-bed use, melanotan exposure and anabolic hormone use.
What a case report can establish is that something happened in a particular person. It cannot establish cause, and the people described often had other exposures.
What can be said without overstating it: a compound that stimulates pigment cells, associated in the published literature with new and changing moles, is not one where a changing mole should be ignored.
One thing it is not
It is also not Melanotan I, the linear analogue afamelanotide — a different molecule with a different receptor profile, an approved implant for a rare photosensitivity disease, and a label that names the darkening of existing moles as an effect to be monitored twice a year.
A tan produced this way is not sun protection. The pigmentation is real; the protective effect people assume comes with it has not been established, and using it as a reason to spend longer in the sun is the exact opposite of what the safety literature would suggest.
Where it stands
Approved as a medicine: nowhere.
United Kingdom: its sale is illegal, as it is in many other countries.
FDA compounding status: melanotan II appears among nominations withdrawn by the nominator, not on the current Category 2 list (page content current 2026-04-22).
Last checked
2026-09-07.