Educational reference only. Informational material drawn from peer-reviewed literature. Not medical advice and not a recommendation to use, dose, or modify any therapy. Decisions about hormone therapy should be made with a qualified healthcare provider.
Overview
Overview
Melanotan II (MT-II) is a synthetic cyclic heptapeptide developed in the 1980s at the University of Arizona by Victor Hruby (chemistry) and Mac Hadley (biology) as a pharmacologic tool to study the melanocortin system and explore protective tanning as a strategy for reducing UV-driven skin cancer. It is a non-selective melanocortin receptor agonist activating MC1R (skin melanocytes → tanning), MC3R/MC4R (CNS → sexual arousal, appetite suppression, nausea), and MC5R (peripheral). The off-target sexual effects observed in early Arizona Phase I research were the foundation that ultimately led to PT-141 (bremelanotide / Vyleesi), now FDA-approved for premenopausal HSDD.
MT-II occupies a distinctive position among research peptides: the same Arizona research program produced two FDA-approved drugs (Scenesse/afamelanotide for EPP, and Vyleesi/bremelanotide for HSDD), but MT-II itself has never been approved by any regulatory authority worldwide. Instead, it has accumulated specific consumer warnings from the US FDA, UK MHRA, Australian TGA, and Irish HPRA, a degree of explicit regulatory pushback rare among research peptides. Despite these warnings, MT-II is widely used for cosmetic tanning outside medical settings, and consumer use is substantial in the UK, Australia, and elsewhere.
MT-II is structurally a near-twin of PT-141: both are cyclic heptapeptides from the same Arizona research, sharing the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-X where MT-II has X = NH₂ (C-terminal amide) and PT-141 has X = OH (C-terminal hydroxyl). This subtle structural difference shifts receptor binding profile and pharmacokinetics but the family resemblance is extensive: the side effect profiles overlap heavily (nausea, hyperpigmentation, BP effects), and both share theoretical melanoma concerns from MC1R activation on melanocytes.
The relationship to PT-141 ([[pt-141]]) matters clinically and regulatorily: PT-141 has a controlled manufacturing process, defined Phase 3 evidence, FDA-approved dosing (1.75 mg SC Vyleesi autoinjector), and explicit safety labeling; MT-II has none of that. Users seeking the central melanocortin effects (sexual desire) have a regulated option in PT-141. Users seeking the broader effects (tanning + sexual + appetite) operate entirely outside approved care.
Forms
Available forms & half-lives
| Form | Approximate half-life |
|---|---|
| Subcutaneous MT-II | ~30 min (parent) |
| Intranasal MT-II | Variable |
| Oral MT-II | Not feasible |
What it does
Main effects
- Skin pigmentation / tanning: Non-selective MC1R activation on melanocytes increases melanin production; darkening occurs with or without UV exposure (though UV synergizes); the original Arizona research goal as a skin-cancer-prevention strategy
- Spontaneous sexual arousal and erections in males: MC3R/MC4R activation in hypothalamic regions; the unanticipated effect from early Arizona Phase I research (Dorr et al. 1996; Wessells et al. 1998) that ultimately led to PT-141/Vyleesi development
- Appetite suppression: Central MC4R activation; sometimes pursued off-label for weight loss; not a validated indication and not a primary target
- Non-selective melanocortin agonism: Activates MC1R + MC3R + MC4R + MC5R; broader receptor profile than PT-141 explains both wider effect spectrum and more pronounced side effects
- Originated three regulatory pathways from the same Arizona Hruby/Hadley program: Melanotan I (afamelanotide) → Scenesse (EMA 2014, FDA 2019) for EPP; PT-141 (bremelanotide) → Vyleesi (FDA June 2019) for HSDD; MT-II itself → never approved, multiple regulatory warnings
- Structural near-twin of PT-141: Both are cyclic heptapeptides Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-X; MT-II has X = NH₂ (amide), PT-141 has X = OH (hydroxyl); subtle but real receptor binding and PK differences
What to watch for
Common side effects
- Nausea and vomiting: Common, particularly during initial 'loading phase' doses; central mechanism (not GI); sometimes paired with antiemetics by users
- Facial flushing: Common, generally transient
- Spontaneous erections / priapism in males: Can be prolonged (1–5 hours); associated with the yawning-stretching complex described in early Arizona research; can become medically urgent if persistent and require urological intervention
- Hyperpigmentation: Generalized skin darkening plus prominent darkening at injection sites; mucosal darkening of gums and lips can occur; may persist after discontinuation
- Mole / nevus changes: Darkening or shape change in existing moles documented in users; complicates dermatologic surveillance for melanoma in MT-II users
- Theoretical melanoma concern is unresolved: 2013 review found no conclusive causal evidence; 2021 review suggested apparent melanoma signal in MT-II users 'can probably be explained by more UV exposure' (MT-II users tan and seek sun); long-term data lacking
- Blood pressure changes: Reported but less prominent than intranasal PT-141 trial findings
- FDA warning letters and enforcement actions: Multiple actions against US vendors over years
- UK MHRA specific consumer warnings: Regulatory campaigns against MT-II use
- Australian TGA active warning campaigns: Consumer advisories
- Irish HPRA reminder notices: About serious health risks from MT-II
- Other European regulatory authorities: Various warnings issued
- Research chemical quality concerns: Identity, concentration, sterility unverified; no pharmaceutical-grade source exists; PT-141/Vyleesi is the only quality-assured melanocortin agonist for sexual function
- Not currently specifically WADA-prohibited but related compounds may fall under broader categories; verify before use in tested sport
Key facts
Key facts worth knowing
- MT-II is a synthetic cyclic heptapeptide with sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂. 7 amino acids; N-terminal acetylation; cyclic constraint between Asp (position 2) and Lys (position 7) side chains; D-phenylalanine at position 4 essential for melanocortin receptor binding; C-terminal amide (NH₂), the key distinction from PT-141's C-terminal hydroxyl (-OH). Molecular weight 1024.18 Da. CAS 121062-08-6.
- University of Arizona origin (1980s): Developed by Victor J. Hruby (peptide chemistry) and Mac E. Hadley (biology/pharmacology). The original research goal was UV-protective pharmacological tanning to reduce skin cancer rates, a legitimate cancer prevention research objective, not cosmetic peptide development. The hypothesis: if skin could be darkened pharmacologically, UV exposure (and resulting skin cancer) could be reduced.
- Three regulatory pathways from the same Arizona research program: (1) Melanotan I (afamelanotide) → Scenesse, EMA 2014 / FDA 2019, for erythropoietic protoporphyria; (2) PT-141 (bremelanotide) → Vyleesi, FDA June 2019, for premenopausal HSDD; (3) MT-II itself → never approved, subject of multiple regulatory warnings. The Arizona program thus produced two FDA-approved drugs while the parent compound remained a research chemical.
- Dorr et al. 1996 Phase I study: Initial human pilot study of MT-II demonstrated tanning effect (target indication) plus unexpected effects: nausea/vomiting, facial flushing, spontaneous erections in male participants, appetite suppression. The erection finding was unexpected and pointed to MC4R-mediated central effects on sexual function, foundational for the PT-141 development pathway. Dorr RT, Lines R, Levine N, Brooks C, Xiang L, Hruby VJ et al. Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sciences 1996;58(20):1777-84.
- Wessells et al. 1998 Journal of Urology: Studied MT-II for erectile dysfunction in men, demonstrating dose-related erectile activity. This work explicitly characterized the sexual effects of MT-II and informed the strategic pivot to PT-141. Wessells H, Fuciarelli K, Hansen J, et al. Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction. Journal of Urology 1998;160(2):389-93.
- Non-selective melanocortin agonism is both the source of useful effects and the source of side effects. MC1R activation → tanning (intended); MC3R/MC4R CNS activation → sexual arousal, appetite suppression, nausea; MC5R peripheral → various effects. The broader receptor profile vs PT-141 (which retains some non-selectivity but has more focused MC4R activity) explains MT-II's more pronounced side effects.
- Multiple regulatory authority warnings: US FDA (multiple warning letters, enforcement actions, public health advisories); UK MHRA (specific consumer warnings, regulatory campaigns); Australian TGA (active warning campaigns advising consumers to avoid); Irish HPRA (reminder notices about serious health risks); other European authorities (various). This degree of explicit regulatory pushback is rare among research peptides and reflects the consumer-marketing context for MT-II ('Barbie Drug' media coverage drove tanning-peptide sales).
- Melanoma concern is unresolved. Theoretical concern from MC1R stimulation on melanocytes. A 2013 review found no conclusive evidence of melanoma causation. A 2021 review concluded that increased melanoma risk in MT-II users 'can probably be explained by more UV exposure', because MT-II users tan and seek sun. Mole/nevus changes are documented and complicate dermatologic surveillance. Long-term safety data lacking. Habbema L, Halk AB, Neumann M, Bergman W. Risks of unregulated use of alpha-melanocyte-stimulating hormone analogues: a review. International Journal of Dermatology 2017 [supersedes 2013 review framework].Recent review (2021) on MT-II and melanoma risk: UV exposure as confounder.
- Structurally near-identical to PT-141, but with critical differences. Both are cyclic heptapeptides from the same Arizona research with shared sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-X. MT-II: X = NH₂ (C-terminal amide). PT-141: X = OH (C-terminal hydroxyl). This subtle structural difference affects receptor binding profile and pharmacokinetics. The clinical-regulatory difference is dramatic: PT-141 is FDA-approved Vyleesi with controlled manufacturing, validated dosing, and explicit safety labeling; MT-II is a research chemical with warnings from 4+ regulatory authorities.
Legal status
Legal status
Never approved by any regulatory authority worldwide. Specific regulatory warnings issued by US FDA, UK MHRA, Australian TGA, Irish HPRA, and other European authorities. Available through unregulated sources and online vendors. Not legal for human use in most jurisdictions. Not currently specifically WADA-prohibited but verify status before use in tested sport. Distinct from approved relatives Scenesse (afamelanotide/Melanotan I) and Vyleesi (bremelanotide/PT-141) which share Arizona research lineage.