Melanotan II

Overview

Melanotan II (MT-II) is a synthetic cyclic heptapeptide derived from the body's own alpha-melanocyte-stimulating hormone (α-MSH). It was developed at the University of Arizona by Victor Hruby and Mac Hadley as part of a research programme into melanotropic peptides for skin pigmentation and protection against skin cancer. The ring in the molecule is a lactam bridge between the side chains of aspartate and lysine: an amide bond that locks the peptide in its active conformation and makes it more metabolically stable.

Melanotan II binds with high affinity to multiple melanocortin receptors: MC1R, which drives pigmentation, and MC3R and MC4R, which act in the central nervous system on behaviour and energy balance. That broad, non-selective receptor activity is both the source of the scientific interest and of the safety concerns.

The peptide went through a single published human phase I study, in 1996, in three male volunteers. That study showed pigmentation at low subcutaneous doses, with nausea and spontaneous erections as the most notable side effects. Those two findings each gave rise to a more selective development line: afamelanotide (Melanotan I, for pigmentation) and bremelanotide (PT-141, for sexual function). Melanotan II itself has never been further developed clinically and is not registered anywhere as a medicine.

Outside the research literature, Melanotan II has a second, problematic existence. It circulates widely on the grey market as a 'tanning peptide', which has prompted several European safety warnings and published case reports of serious adverse events. That context is inseparable from this compound and is addressed separately below.

Mechanism of action

Melanotan II activates the melanocortin receptors MC1R, MC3R and MC4R. The broad, superpotent activity explains both the pigmentation and the central and metabolic effects. It also explains the complex side-effect profile.

MC1R and pigmentation

• Binds with high affinity to MC1R on the pigment cells (melanocytes).
• Stimulates cAMP production and activates tyrosinase, the key enzyme in melanin synthesis. cAMP is an intracellular messenger.
• Induces pigmentation in multiple skin areas after subcutaneous administration.

MC4R in the central nervous system

• Activates MC4R in the hypothalamus, the same pathway later refined selectively in PT-141.
• In the early human study, MC4R activation was linked to spontaneous erections.
• MC4R is also a central regulator of appetite and energy expenditure; in animal models MT-II affects thermogenesis via this route.

Broad, non-selective activity

• At active doses MC1R, MC3R and MC4R are all engaged.
• That broader activity, compared with the more selective PT-141, gives a more complex side-effect profile.
• MC3R activation has been linked to nausea.

Research findings

• In three male volunteers, MT-II produced measurable skin pigmentation at low subcutaneous doses, quantitatively confirmed by reflectance measurements (Dorr 1996).
• Nausea was the most consistent side effect in that phase I study.
• Spontaneous erections were an unexpected finding, the direct trigger for the development of PT-141.
• A published case report describes systemic toxicity with sympathomimetic features and rhabdomyolysis after a self-administered injection; the substance was confirmed as MT-II by mass spectrometry (Nelson 2012). Rhabdomyolysis is breakdown of muscle tissue.
• A second case report describes a renal infarction most likely attributed to MT-II (Peters 2020).
• A BMJ editorial flagged widespread use in the general population and the associated risks (Evans-Brown 2009).
• In vitro MT-II shows superpotent melanotropic activity compared with α-MSH.
• In a mouse model, MT-II affected thermogenesis via the central melanocortin system (McMillan 2020).

Human phase I data (1996)

• Measurable skin pigmentation at low subcutaneous doses in 3 male volunteers (Dorr 1996), quantitatively confirmed by reflectance measurements.
• Nausea as the most consistent side effect.
• Spontaneous erections as an unexpected finding, the direct trigger for the development of PT-141.

Human safety signals (grey market)

• Case report of systemic toxicity with sympathomimetic features and rhabdomyolysis after a self-administered injection; the substance was confirmed as MT-II by mass spectrometry (Nelson 2012).
• Second case report of a renal infarction most likely attributed to MT-II (Peters 2020).
• BMJ editorial flagging widespread use in the general population and associated risks (Evans-Brown 2009).

Preclinical and pharmacological data

• Superpotent melanotropic activity in vitro relative to α-MSH.
• Broad MC1R/MC3R/MC4R activity has been pharmacologically characterised.
• In a mouse model, MT-II affected thermogenesis via the central melanocortin system (McMillan 2020).

Research context

Melanotan II holds an unusual historical position in melanocortin pharmacology. The 1996 phase I study was small but consequential: it directly produced two more selective compounds that did complete full development, namely afamelanotide and bremelanotide. In that sense MT-II is mainly interesting as a historical reference compound for broad melanocortin activation, in contrast with the sharper profiles of its successors.

The boundary of usable knowledge is sharp here. The human evidence on MT-II itself consists of one study in three people. Everything that has since been published about the peptide in humans does not come from controlled research, but from case reports of adverse events following grey-market use: rhabdomyolysis, renal infarction, sympathomimetic toxicity. That is an unusual and telling ratio: the evidence for harm is more recent and more concrete than the evidence for controlled efficacy.

That safety picture makes MT-II a compound that requires especially careful, strictly scientific positioning. Its broad, non-selective receptor profile makes effects in humans hard to predict, and the combination of MC1R activation with pre-existing pigmented lesions raises questions that remain unanswered. The peptide is not registered as a medicine in the EU and is the subject of multiple national safety warnings.

Open questions

Melanotan II is a historically interesting model for melanocortin pharmacology, but the combination of one published phase I study, multiple published case reports of toxicity from grey-market use, and European safety warnings requires an exceptionally careful, research-use-only framing.

• Human data is limited to one phase I study in three male volunteers; there is no full clinical development.
• The long-term safety profile has not been systematically investigated in a controlled setting.
• The risk of changes in melanocytic nevi and possible stimulation of melanoma via MC1R is not fully characterised.
• The non-selective receptor profile makes side-effect prediction in humans complex.
• Interaction with pre-existing melanocytic lesions has not been adequately investigated.
• The substance is not EMA-registered; its regulatory status in the EU calls for caution.

Research outlook

The more selective derivatives afamelanotide and bremelanotide have largely supplanted the therapeutic development of Melanotan II.

Melanotan II remains relevant as a pharmacological reference compound for melanocortin receptor research.

Structure–activity relationships of melanocortin analogues remain an active area of research.

The safety profile of MC1R activation in people with pigmented lesions deserves further study.

Scientific interest

Melanocortin receptor pharmacology and receptor selectivity

MC1R-mediated melanogenesis

Historical model for the development of melanotropic peptides

Comparative pharmacology with PT-141 and afamelanotide

Specifications

References

1. Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. · Dorr RT, Lines R, Levine N, et al. · Life Sciences · 1996
2. Discovery and development of novel melanogenic drugs. Melanotan-I and -II. · Hadley ME, Hruby VJ, Blanchard J, et al. · Pharm Biotechnol · 1998
3. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. · Hadley ME, Dorr RT. · Peptides · 2006
4. Use of melanotan I and II in the general population. · Evans-Brown M, Dawson RT, Chandler M, McVeigh J. · BMJ · 2009
5. Melanotan II injection resulting in systemic toxicity and rhabdomyolysis. · Nelson ME, Bryant SM, Aks SE. · Clin Toxicol · 2012
6. Melanotan II: a possible cause of renal infarction. · Peters B, Hadimeri H, Wahlberg R, Afghahi H. · CEN Case Rep · 2020
7. Melanotan II partially rescues the impaired thermogenic capacity of PACAP-deficient mice. · McMillan TR, Forster MAM, Short LI, et al. · Exp Physiol · 2020
8. Targeting the central melanocortin system for the treatment of metabolic disorders. · Sweeney P, Gimenez LE, Hernandez CC, Cone RD. · Nat Rev Endocrinol · 2023

Availability

In stock · Batch PEP-MT2-2026-01 · HPLC 99.27 % · released 16 Jul 2026

• Melanotan II 10 mg · product page with price and batch CoA