Educational reference, not medical advice. This page summarizes information from published research and regulatory filings for educational purposes. It is not a recommendation to use any compound and should not replace guidance from a licensed healthcare provider. Most peptides discussed here are not approved for the uses described.
What it is
Melanotan II (MT-II, MT2) is a synthetic cyclic seven-amino-acid analog of alpha-melanocyte-stimulating hormone with a lactam bridge that locks the molecule into a bioactive conformation. The cyclization makes MT-II both substantially more potent and much less selective than the linear Melanotan I — it agonizes MC1 (skin pigmentation), MC3, MC4 (sexual arousal, appetite suppression, nausea), and MC5 receptors with relatively similar affinity.
It is the most popular grey-market tanning peptide sold today, despite never having been approved for any indication anywhere.
History
MT-II was synthesized in the Hadley and Hruby laboratories at the University of Arizona around 1980 as part of the same alpha-MSH analog program that produced Melanotan I (afamelanotide). The early Phase 1 work by Robert Dorr and colleagues in the 1990s documented the tanning effect and the most prominent side effects: nausea, spontaneous penile erection in male subjects, and transient appetite suppression.
The MC4-mediated sexual-arousal effect that emerged from those early trials was eventually developed into a separate compound — bremelanotide (PT-141) — which became the FDA-approved drug Vyleesi. The MC1-mediated tanning effect was developed into the linear analog Melanotan I, which became Scenesse for EPP. Melanotan II itself, with its broad multi-receptor profile, was abandoned by Clinuvel Pharmaceuticals in the 2000s as the cleaner alternatives advanced.
Use persisted outside the regulatory system. Through the 2000s and 2010s, MT-II became one of the most common research peptides sold online, marketed primarily for cosmetic tanning. Multiple national health agencies — in the UK, Australia, Sweden, Denmark, and elsewhere — have issued public warnings about its sale and use. Case reports of melanoma diagnosed in users have been published, along with cases of rhabdomyolysis, priapism, and severe systemic reactions.
Regulatory status
Not approved by any regulator. Not on the FDA 503A bulk substances list, so US compounding pharmacies cannot legally prepare it for patients. Sold extensively through online research peptide vendors with not-for-human-use labeling. The UK Medicines and Healthcare products Regulatory Agency has classified MT-II as an unlicensed medicine and taken enforcement action against suppliers; the Therapeutic Goods Administration in Australia has done the same.
How researchers describe its action
MT-II activates MC1 receptors on melanocytes to drive eumelanin synthesis, producing a darker, more uniform tan than would arise from UV exposure alone. The same compound also activates MC4 receptors in the hypothalamus, producing the characteristic sexual arousal, appetite suppression, and nausea reported by users. MC5 activation may contribute to sebaceous gland effects.
The non-selective profile is the central problem with the compound from a drug-development standpoint: it is difficult to achieve the cosmetic tanning effect without also producing the central nervous system effects, and dose escalation tends to produce all of them together.
Half-life and dosing intervals
Published estimates of MT-II's plasma half-life range from 30 minutes to roughly an hour after subcutaneous injection. The tanning effect persists for weeks because the underlying melanogenesis is a slow biological process, not because the peptide itself remains in circulation.
There is no established dose. Observational use protocols typically describe a "loading phase" of small daily subcutaneous injections (0.25 to 1 mg per day, often started at 0.1 mg to test tolerance) for one to several weeks until visible pigmentation appears, followed by a "maintenance phase" of one to two doses per week. UV exposure is generally required for the tanning response to develop. None of these protocols comes from controlled human trials.
Reconstitution example
Melanotan II is typically supplied lyophilized in 10 mg vials. A 10 mg vial reconstituted with 2 mL of bacteriostatic water yields 5 mg/mL. On a 1 mL U-100 insulin syringe, 5 units (0.05 mL) delivers 250 mcg, and 10 units (0.10 mL) delivers 500 mcg. Vial's calculator handles the conversion when vial mass and water volume are entered.
What to know
- Not approved, anywhere. No regulator has authorized MT-II for any use. Multiple national agencies have explicitly warned against its sale and use.
- Distinct from Melanotan I. Melanotan I is afamelanotide, an FDA-approved drug delivered as an implant for EPP. Melanotan II is a different molecule and an unapproved one.
- Documented adverse events. Published case reports include melanoma in users, rhabdomyolysis, priapism, severe hypertension, and anaphylaxis. The published series are not representative samples and the true rates are unknown.
- Mole darkening and surveillance. MT-II darkens existing moles and can produce new pigmented lesions. This complicates dermatologic surveillance for melanoma in users.
- Product quality varies. Mass-spectrometry analyses of online-purchased MT-II have found variable purity, mislabeling, and bacterial contamination.
- Storage. Lyophilized: refrigerate, protect from light. Reconstituted: refrigerate; the small unprotected peptide degrades more rapidly than the modified D-amino acid analogs.
Sources
- 1.Dorr RT et al. (1996). Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sciences.
- 2.Hjuler KF, Lorentzen HF (2014). Melanoma associated with the use of melanotan-II. Dermatology.
- 3.Habbema L et al. (2017). Risks of unregulated use of alpha-melanocyte-stimulating hormone analogues: a review. International Journal of Dermatology.
- 4.Nelson ME et al. (2012). Melanotan II injection resulting in systemic toxicity and rhabdomyolysis. Clinical Toxicology.
- 5.Breindahl T et al. (2015). Identification and characterization by LC-UV-MS/MS of melanotan II skin-tanning products sold illegally on the Internet. Drug Testing and Analysis.