Melanotan II (MT-II / MT-2)

Melanotan II is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2. Its CAS number is 121062-08-6, and its molecular weight is 1,024.2 Da. Developed at the University of Arizona in the 1990s, it was designed as a more potent and stable analog of alpha-melanocyte-stimulating hormone (alpha-MSH). MT-II activates melanocortin receptors non-selectively, which explains its diverse effects. MC1R stimulation in melanocytes drives eumelanin production (tanning). MC4R activation in the central nervous system produces the sexual arousal, erectile function, and appetite suppression that users often report. The non-selectivity is both the appeal and the problem: you cannot get the tanning without the other effects, and the broad receptor activation creates a wide side effect profile. The only formal clinical study was a Phase I pilot (Dorr et al., Life Sciences 1996, PMID: 8637402) that administered 5 low subcutaneous doses every other day to healthy volunteers. It confirmed measurable tanning activity and documented spontaneous penile erections lasting 1-5 hours post-dose, along with a characteristic yawning/stretching complex. Since then, no Phase 2 or Phase 3 trials have been conducted with MT-II. Instead, the literature consists of case reports documenting serious adverse events. A 2020 report in CEN Case Reports (PMID: 31953620) described a 27-year-old who developed right renal infarction affecting approximately 50% of the kidney after using 27 mg cumulative MT-II over 6 months. The mechanism likely involved thrombotic effects and possible direct renal parenchymal toxicity. Multiple cases of rhabdomyolysis have been documented. The melanoma question is critical. MT-II stimulates melanocyte proliferation, and case reports have documented melanoma coinciding with MT-II use. A 2021 review concluded that the increased melanoma risk in MT-II users is likely attributable to increased UV exposure (sun-seeking behavior after achieving a tan), but the combination of melanocyte stimulation plus UV exposure creates a particularly concerning risk profile. MT-II also darkens existing moles, making clinical skin surveillance unreliable because new or changed moles may be masked by the overall pigmentation increase. MT-II is NOT approved by any regulatory agency in the world. The FDA, Australia's TGA, and the UK's MHRA have all issued public warnings against its use. It is expected to remain on the FDA Category 2 restricted list, unlike the approximately 14 peptides being returned to Category 1 under the 2026 HHS reclassification. One thing to get right: Melanotan II should not be confused with afamelanotide (Melanotan I, brand name Scenesse), which IS FDA-approved (October 2019) for erythropoietic protoporphyria. Afamelanotide is a selective MC1R agonist with a different safety profile and legitimate medical use. MT-II's non-selective melanocortin activation produces very different pharmacology. Individuals with fair skin (Fitzpatrick types I-II), red hair, or MC1R gene variants are at elevated baseline melanoma risk and should be especially cautious. Strong contraindications include any personal or family history of melanoma or dysplastic nevi, cardiovascular disease, renal disease, and pregnancy.