Melanotan II (often written MT-II) is a synthetic cyclic peptide built to mimic alpha-melanocyte-stimulating hormone (alpha-MSH). It is a seven-amino-acid cyclic analog with the molecular formula C50H69N15O9 (PubChem CID 92432, CAS 121062-08-6). Chemists at the University of Arizona began designing alpha-MSH analogs in the 1980s as potential tanning agents, and Melanotan II came out of that work.
It belongs to the melanocortin agonist class. Unlike its better-known cousin afamelanotide (Melanotan I), MT-II is non-selective: it activates the melanocortin receptors MC1, MC3, MC4, and MC5. That receptor spread is what drives both its intended and unintended effects.
How it is thought to work
Activating MC1 receptors on skin melanocytes pushes those cells toward producing eumelanin, the brown-black pigment, which darkens skin without sun exposure. Activating MC4 receptors in the brain affects appetite and sexual arousal. So a compound aimed at tanning also tends to suppress appetite and trigger erections, because the same molecule hits several receptors at once.
What the research actually shows
There is real peer-reviewed human data on MT-II, though the trials were small and decades old. The most cited work came from Hunter Wessells and colleagues at the University of Arizona, who studied it for erectile dysfunction rather than tanning.
- In a double-blind, placebo-controlled crossover trial published in Urology in 2000, ten men with erectile dysfunction received MT-II at 0.025 mg/kg by subcutaneous injection. The peptide produced subjectively reported erections in 12 of 19 injections, versus 1 of 21 placebo doses. See Wessells et al., 2000.
- Related work on melanocortin agonists and penile erection is summarized in Wessells et al., *Int J Impot Res*, 2000.
Those same studies flagged the problems. Nausea and stretching or yawning were more common with MT-II, and several injections caused severe nausea. Development as a drug never went past early-stage trials. Palatin Technologies stopped working on MT-II around 2000 and instead pursued bremelanotide, a related compound that is essentially a metabolite of MT-II. Bremelanotide was later approved as Vyleesi for a different indication.
It helps to keep Melanotan II separate from Melanotan I. Melanotan I, afamelanotide, was approved by the FDA in 2019 as Scenesse to reduce phototoxicity in adults with erythropoietic protoporphyria, a rare disease. Melanotan II has no such approval anywhere.
Regulatory and safety status
Melanotan II is not approved for human use in the United States, the UK, the EU, or any other major jurisdiction. The FDA, the UK MHRA, and other agencies have issued warnings about products sold as melanotan since around 2007, and the FDA has sent warning letters to companies marketing it. The products circulating online are unregulated and are not legal to sell for human consumption.
Reported adverse effects include facial flushing, nausea, reduced appetite, and prolonged erections; one researcher described an eight-hour erection after an accidental overdose. Case reports have linked MT-II use to changing moles and melanoma, although a 2021 review noted the higher melanoma signal in users could partly reflect more UV exposure rather than the drug itself. DermNet has a clinician-facing summary.
For buyers: the testing angle
Because Melanotan II is sold only as a research chemical, there is no regulated manufacturing standard behind it. Identity and purity vary by supplier, and unregulated peptides can contain the wrong compound, degradation products, or contaminants. If a vendor sells it, the only meaningful quality signal is an independent, batch-specific certificate of analysis from a third-party lab confirming identity and purity. peptideone aggregates published COAs and third-party vendor ratings so buyers can compare what is actually documented.
Nothing here is medical or dosing advice. Melanotan II is research-use-only and is not approved for human consumption.