Melanotan II
Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 (Melanotan-II, MT-II); also written Ac-Nle4-Asp5-His6-D-Phe7-Arg8-Trp9-Lys10 α-MSH4-10-NH2
Access and compounding status raise extra safety and legal questions.
A synthetic peptide that darkens skin (tanning effect), increases sexual arousal, and suppresses appetite by activating certain hormone receptors throughout the body. Multiple human studies have examined these effects, but it has no regulatory approval anywhere and its safety profile requires careful consideration due to its wide-ranging effects on the body.
This entry is a cited research summary, not an established treatment reference. Dosing language is included as source context, not as medical instruction.
Safety Summary
The most commonly reported side effect is nausea, which is dose-dependent and may diminish with repeated use. The Phase I study described it as 'mild nausea, not requiring antiemetic treatment' at most dose levels (PMID 8637402), while the Wessells et al. study reported 'a low percentage experiencing severe nausea'. Facial flushing and spontaneous penile erections were observed in the Phase I study, with erections lasting 1-5 hours depending on dose (PMID 8637402). Appetite suppression is a direct MC4R-mediated effect (PMID 10951699). Dermatological concerns include darkening of existing moles and appearance of new nevi, documented in multiple case reports. Oral mucosa pigmentation was documented in a 2026 case report, with buccal pigmentation resolving after 1 month but gingival pigmentation persisting with reduced intensity at 3 months (PMID 41752902). The FDA Category 2 listing cites published case reports of melanoma, posterior reversible encephalopathy syndrome, sympathomimetic toxidrome, and priapism. A case of melanotan-induced priapism required cavernosal aspiration and irrigation with intracavernosal phenylephrine injection; the patient did not recover erectile function at 4-week follow-up. Rhabdomyolysis has been reported in case reports. The melanoma risk question remains unresolved: a 2013 review found no conclusive evidence MT-II causes melanoma. and a 2021 review concluded that increased melanoma risk in MT users can probably be explained by more UV exposure.
Clinical check-in
If real-world use or exposure is being considered, review potential interactions, contraindications, and monitoring needs with a licensed clinician rather than relying on summary copy alone.
Sources: [1-13]