Melanotan II

Overview

Melanotan II (MT-II) is a synthetic cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone (alpha-MSH), developed in the early 1990s at the University of Arizona by Victor Hruby and Mac Hadley. The original research objective was to create a compound that could stimulate melanogenesis (skin darkening) without UV exposure, as a potential preventive strategy against skin cancer in fair-skinned populations.

During clinical trials, researchers observed that MT-II produced significant secondary effects beyond tanning — most notably, spontaneous penile erections in male subjects and increased sexual desire in both sexes. These observations led to the development of PT-141 (bremelanotide), a derivative optimized for pro-sexual effects that eventually received FDA approval.

MT-II is a non-selective melanocortin receptor agonist, binding to MC1R (pigmentation), MC3R, MC4R (sexual function, appetite, fat metabolism), and MC5R with varying affinities. This broad receptor activation profile is responsible for its multiple physiological effects but also contributes to its safety concerns.

MT-II has never received regulatory approval in any jurisdiction. It is classified as an unregulated research compound and is widely available through gray-market peptide suppliers. Despite regulatory warnings from agencies including the FDA, TGA (Australia), and EMA (Europe), it is one of the most widely used unregulated peptides globally, particularly for cosmetic tanning purposes.

Structure

MT-II is a cyclic heptapeptide with the following structure:

Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂

• Molecular formula: C₅₀H₆₉N₁₅O₉
• Molecular weight: 1,024.18 g/mol
• CAS Number: 121062-08-6

Structural comparison with PT-141:

• MT-II and PT-141 share the same cyclic core structure (Asp-His-D-Phe-Arg-Trp-Lys)
• MT-II has a C-terminal amide (-NH₂); PT-141 has a C-terminal free acid (-OH)
• Both contain the His-D-Phe-Arg-Trp pharmacophore essential for melanocortin receptor binding

The cyclic structure (lactam bridge between Asp and Lys) is critical for:

• Enhanced metabolic stability compared to linear alpha-MSH
• Improved receptor binding affinity
• Extended biological activity duration

Mechanism of Action

MC1R Activation (Melanogenesis)

The primary intended effect of MT-II is skin darkening through MC1R activation on melanocytes:

• MC1R signaling activates adenylyl cyclase and increases intracellular cAMP
• Elevated cAMP activates the MITF (microphthalmia-associated transcription factor) pathway
• MITF upregulates tyrosinase, TRP-1, and TRP-2 — the key enzymes in melanin synthesis
• Results in increased eumelanin production, producing skin darkening independent of UV exposure
• UV exposure acts synergistically with MT-II, producing more pronounced tanning than either stimulus alone

MC3R/MC4R Activation (Sexual Function)

MT-II activates the same hypothalamic melanocortin pathways as PT-141:

• MC4R activation in the paraventricular nucleus triggers oxytocin release
• Enhanced dopaminergic signaling in mesolimbic reward circuits
• Central pro-sexual effects in both males and females
• Erections in males can occur spontaneously (without sexual stimulation)

MC4R Activation (Appetite and Fat Metabolism)

MC4R activation in the hypothalamus also modulates energy balance:

• Suppression of appetite through activation of anorexigenic POMC/CART neurons
• Inhibition of orexigenic NPY/AgRP signaling
• Potential direct effects on lipid metabolism through peripheral MC4R activation
• Appetite suppression is dose-dependent and can be pronounced

MC3R Effects

MC3R activation contributes to:

• Fat metabolism modulation
• Inflammatory response regulation
• Additional appetite and energy balance effects distinct from MC4R

Research Summary

Area of Study	Key Finding	Notable Reference
Melanogenesis	Significant skin darkening without UV exposure in fair-skinned subjects; enhanced tanning response when combined with UV	Dorr et al., Life Sciences, 1996
Sexual function (male)	Spontaneous erections observed in early clinical trials; dose-dependent pro-erectile effect	Wessells et al., Annals of the New York Academy of Sciences, 2003
Sexual function (female)	Increased sexual desire and arousal reported by female subjects in clinical trials	Diamond et al., Journal of Sexual Medicine, 2006
Appetite suppression	Dose-dependent reduction in food intake; MC4R-mediated anorexigenic effect	Fehm et al., Journal of Clinical Endocrinology & Metabolism, 2001
Fat metabolism	Reduced fat mass independent of caloric intake in animal models; MC4R-mediated lipolytic effects	Haskell-Luevano et al., Peptides, 2009
Nevi changes	Case reports of darkening, growth, or morphological changes in pre-existing moles	Langan et al., British Journal of Dermatology, 2009
Rhabdomyolysis	Case report of rhabdomyolysis in a bodybuilder using MT-II	Devlin and Manoukian, BMJ Case Reports, 2008
Quality control	Analysis of gray-market MT-II products found significant variability in purity, potency, and contaminants	Evans-Brown et al., BMJ Open, 2012
Nausea profile	Nausea is the most common adverse effect (30–50%); typically occurs in early dosing and may attenuate	Dorr et al., Life Sciences, 1996
Renal effects	Case report of focal segmental glomerulosclerosis associated with MT-II use	Centers for Disease Control case data

Pharmacokinetics

• Half-life: Approximately 1–2 hours
• Onset of tanning effect: Visible darkening typically reported after 5–10 days of regular dosing in community reports
• Onset of sexual effects: 1–3 hours post-injection
• Duration of sexual effects: 4–8 hours
• Route: Subcutaneous injection (standard); intranasal (lower and variable bioavailability)
• Metabolism: Enzymatic degradation; the cyclic structure provides moderate protease resistance
• Tanning persistence: Skin darkening can persist for weeks to months after discontinuation, gradually fading as melanocytes turn over

Notable Adverse Effects

• Nausea: 30–50% incidence, particularly with initial doses; dose-dependent
• Facial flushing: Common, typically transient
• Mole darkening/changes: New or altered nevi; a significant safety concern as it may mask melanoma detection
• Spontaneous erections: Can be socially inconvenient; dose-dependent
• Injection site reactions: Redness, irritation at injection sites
• Fatigue/lethargy: Reported by some users, particularly at higher doses
• Blood pressure changes: Small transient increases

Dosing Protocols

The following dosing information is compiled from published research and community discussion for educational purposes only. No FDA-approved human dosing guidelines exist for Melanotan II. Always consult a qualified healthcare professional.

Community-Discussed Protocol (Loading + Maintenance)

Phase	Dose	Frequency	Duration
Loading	250–500 mcg	Once daily	1–2 weeks
Maintenance	250–500 mcg	2–3x weekly	Ongoing as desired

Reconstitution (10 mg vial)

• Add 2.0 mL bacteriostatic water → 5.0 mg/mL concentration
• At this concentration: 1 unit = 50 mcg on a U-100 insulin syringe
• 250 mcg = 5 units | 500 mcg = 10 units

Key Points

• Route: Subcutaneous injection
• Injection timing: Many users inject before bed to sleep through initial nausea
• Onset of tanning: Visible darkening typically reported after 5–10 days of loading
• UV exposure: Tanning effect is enhanced with moderate UV exposure during loading phase
• Common side effects: Nausea (30–50%), facial flushing, mole darkening — nausea typically attenuates with continued use
• Safety concern: Monitor moles closely — MT-II can darken existing nevi and potentially mask melanoma

Dosing Protocols

The following dosing information is compiled from published research and community discussion for educational purposes only. No FDA-approved human dosing guidelines exist for most research peptides. Always consult a qualified healthcare professional.

Reconstitution

Parameter	Value
Vial size	10 mg
Bacteriostatic water	3.0 mL
Concentration	~3,333 mcg/mL
Storage (reconstituted)	2-8 °C, use within 1-2 weeks
Storage (lyophilized)	-20 °C

Dosing Schedule (Loading Phase)

Week	Dose	Frequency	Syringe units
1	250 mcg	Once daily	7.5 units
2	500 mcg	Once daily	15 units
3	750 mcg	Once daily	22.5 units
4-8	1,000 mcg	Once daily	30 units

Maintenance Phase

Dose	Frequency
500-1,000 mcg	1-2x per week

Cycle Guidelines

• Loading phase: 6-8 weeks daily injections
• Maintenance: 1-2 injections per week to sustain pigmentation
• Route: Subcutaneous injection
• Maximum: Do not exceed 2 mg per day
• Injection sites: Rotate between abdomen, thighs, and upper arms
• Side effects: Nausea is common (30-50%) especially early; facial flushing; monitor moles closely for changes

Common Discussion Topics

1. Safety concerns — mole changes — The most serious safety discussion. MT-II can darken existing moles and potentially stimulate melanocyte proliferation. Dermatologists have raised concerns that this could mask early melanoma detection or theoretically promote melanocyte transformation in predisposed individuals.

2. Regulatory warnings — Multiple regulatory agencies (FDA, TGA, MHRA, EMA) have issued warnings about MT-II. Australia's TGA has been particularly active in enforcement due to high rates of unregulated use.

3. Product quality — As an unregulated compound, MT-II purchased from gray-market suppliers varies significantly in purity, potency, and sterility. Published analyses have identified bacterial contamination, incorrect peptide content, and unknown impurities.

4. Loading and maintenance protocols — Community-developed dosing protocols typically involve a "loading phase" of daily injections followed by a reduced "maintenance" frequency, though no clinically validated protocols exist.

5. MT-II vs. PT-141 for sexual effects — Comparison with PT-141, which was specifically optimized for pro-sexual effects without significant melanogenic activity.

6. Appetite suppression for weight loss — Some community use is motivated by MT-II's anorexigenic effects, though this application has no clinical evidence base and carries additional risks.

7. Sunless tanning alternative — The original research rationale — reducing UV exposure-related skin cancer risk — is sometimes cited, though the safety profile of unregulated MT-II likely offsets any theoretical UV-reduction benefit.

Related Compounds

• PT-141 (Bremelanotide) — derived from MT-II; FDA-approved for HSDD; retains sexual effects without significant tanning
• Melanotan I (Afamelanotide/Scenesse) — a linear MC1R-selective analog; EMA-approved for erythropoietic protoporphyria; produces tanning with fewer non-melanogenic side effects
• Alpha-MSH — the endogenous hormone from which MT-II was designed
• Setmelanotide (Imcivree) — an MC4R agonist FDA-approved for rare genetic obesity; demonstrates therapeutic MC4R targeting
• AOD-9604 — unrelated structurally but sometimes discussed alongside MT-II for fat metabolism applications