Melanotan II

II. What is this compound?

Melanotan II (MT-II) is a cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 and a molecular weight of approximately 1024.2 daltons. It is a superpotent, metabolically stabilized analogue of α-melanocyte-stimulating hormone (α-MSH), one of the melanocortin peptides derived from the proopiomelanocortin (POMC) precursor.

The key pharmacological property that defines MT-II — and distinguishes it from its descendant PT-141 PT-141 cyclic heptapeptide lactam / melanocortin receptor agonist Melanocortin receptor agonist studied for sexual desire, arousal & CNS-mediated erectile function — is that it is non-selective across the melanocortin receptor family. It activates MC1R (pigmentation), MC3R and MC4R (appetite and sexual function), and MC5R, whereas bremelanotide is comparatively more focused on the MC3R/MC4R sexual-function receptors [3] PMID: 17584134 . This broad activation is why MT-II produces tanning, appetite suppression, and sexual arousal simultaneously — and why its side-effect profile is correspondingly broad.

MT-II's original rationale was photoprotection. By stimulating MC1R on epidermal melanocytes, it drives eumelanin synthesis and skin darkening independent of ultraviolet exposure — the theory being that a UV-independent tan might reduce sun-seeking behavior and skin-cancer risk [4] PMID: 8637535 . That premise, as later dermatology reports would complicate, sits uneasily beside evidence that the same compound can alter the behavior of pigmented lesions.

III. How it works

The core mechanism of Melanotan II is broad, non-selective activation of melanocortin receptors — and each receptor subtype it engages explains a different part of its effect profile.

MC1R activation drives the pigmentation for which the peptide was designed. On epidermal melanocytes, MC1R signaling upregulates eumelanin production, darkening the skin without requiring UV-induced DNA damage as the trigger [5] PMID: 8637535 . The tan appears within days of dosing and can persist for weeks, far outlasting the peptide's short circulating half-life.

MC3R and MC4R activation in the hypothalamus mediates the sexual-function effects. Melanocortin signaling in central arousal circuits — the same paraventricular-nucleus pathways later exploited therapeutically by bremelanotide — produces erections and increased sexual desire [6] PMID: 9474129 . This was the unexpected observation that reframed the entire research program: a tanning peptide revealed a central, brain-level lever on sexual arousal [7] PMID: 15992957 .

MC4R activation also suppresses appetite, consistent with the well-established role of hypothalamic melanocortin tone in energy balance. Users frequently report reduced food intake, and this is a predictable pharmacological consequence rather than an incidental effect.

The unifying theme is that MT-II's lack of receptor selectivity means its effects cannot be cleanly separated. You cannot activate the pigmentation pathway with MT-II without also engaging the arousal, appetite, and cardiovascular melanocortin circuits — which is the fundamental pharmacological reason a more selective successor ( PT-141 PT-141 cyclic heptapeptide lactam / melanocortin receptor agonist Melanocortin receptor agonist studied for sexual desire, arousal & CNS-mediated erectile function ) was pursued for sexual medicine.

• Non-selective agonism across melanocortin receptors (MC1R, MC3R, MC4R, MC5R) — unlike the more MC3R/MC4R-selective metabolite bremelanotide (PT-141)
  PMID 17584134
• MC1R activation on epidermal melanocytes stimulates eumelanin synthesis (melanogenesis), producing skin darkening independent of UV exposure
  PMID 8637535
• Central MC3R/MC4R activation in hypothalamic circuits mediates erectile and sexual-arousal responses — the effect that redirected melanocortin research toward sexual dysfunction and led to bremelanotide
  PMID 9474129PMID 15992957

IV. Research Findings

The evidence base for Melanotan II is thin and early-phase — a critical point given how it is marketed. No large, modern, controlled trials support its use, and no regulator has judged its benefit-risk balance acceptable.

For skin pigmentation, the supporting data come from small phase-I academic work. Early University of Arizona studies demonstrated that subcutaneous MT-II produced measurable, UV-independent tanning, establishing proof of concept for melanocortin-driven photoprotection [8] PMID: 8637535 . What these studies did not establish is long-term safety, an appropriate dose, or whether induced pigmentation meaningfully reduces skin-cancer risk in practice.

For sexual function, the data are phase-II and historically important but limited. A double-blind, placebo-controlled crossover study reported that MT-II initiated erections in men with psychogenic erectile dysfunction, and a follow-up examined organic erectile dysfunction and sexual desire [9] PMID: 9474129 [10] PMID: 10792262 . These findings were scientifically pivotal — they proved a central melanocortin mechanism for erection — but the development pathway moved to the more selective metabolite bremelanotide precisely because MT-II's broad activity and side effects made it unsuitable as a therapeutic.

The honest summary is that Melanotan II's main legacy is scientific rather than clinical: it revealed a mechanism that a safer, approved successor now exploits. As a product for human use, its studied 'benefits' are not matched by any evidence of an acceptable safety margin.

• skin-pigmentation-tanning phase_1_clinical
  PMID 8637535
• erectile-function phase_2_clinical
  PMID 9474129PMID 10792262

V. Dosage Context Explained

There is no validated, safe human dose of Melanotan II, and nothing here should be read as a dosing recommendation. The compound is not an approved medicine; product sold online is unlicensed, of unknown purity, and often mislabeled.

The only human dosing figures in the literature come from small academic studies, where subcutaneous MT-II was administered at roughly 0.025 mg/kg under clinical supervision [11] PMID: 8637535 . These figures describe what researchers used in a controlled setting decades ago — not a protocol for consumer use. Real-world use is unstandardized, and the gap between a research dose and an unregulated vial of unknown concentration is exactly where harm occurs.

Two structural problems make 'dosing' MT-II uniquely hazardous: - Non-selectivity: any dose that produces tanning also engages the appetite, sexual, and cardiovascular melanocortin circuits. - Supply risk: because the product is illegal to sell for human use, there is no quality control on purity, sterility, or actual peptide content.

For anyone weighing the underlying goal, the responsible framing is that the pigmentation objective does not justify the compound's safety profile, and the sexual-function objective is better served by the approved, more selective successor discussed on our PT-141 PT-141 cyclic heptapeptide lactam / melanocortin receptor agonist Melanocortin receptor agonist studied for sexual desire, arousal & CNS-mediated erectile function page.

• Administration Routes

  subcutaneous

  Range

  reported in early studies at roughly 0.025 mg/kg; consumer use is unstandardized and unverified

  Dosing figures come from small academic studies and are NOT a recommendation. There is no validated safe dose for human use, and product purity in the unregulated market is unknown.

  PMID 8637535

VI. Side Effects: Research Context

Melanotan II's side-effect profile is the reason it never became a medicine — and the reason regulators warn against it.

Acute effects are common. Nausea and facial flushing were frequently observed even in early supervised dosing, and spontaneous penile erections were a recurring finding in male subjects — a direct consequence of central melanocortin activation [12] PMID: 8637535 [13] PMID: 9474129 .

The pigmentary risks are the most serious concern. Beyond generalized darkening of skin, lips, and gums, dermatology case literature has described darkening, enlargement, and rapid change of existing moles and the appearance of new melanocytic naevi in people using melanotan products. Because changing moles are a cardinal warning sign monitored for melanoma, this is not a cosmetic footnote — it complicates skin cancer surveillance and is why a personal or family history of melanoma or atypical naevi is a strong reason to avoid the compound. (These reports come from published case series; readers should treat the association as a documented safety signal rather than a quantified risk.)

Priapism — a prolonged, painful erection — has been reported and is a urological emergency that can cause permanent damage if untreated.

Supply-side harm compounds the pharmacology. Because MT-II is sold illegally and unregulated, injected product may be non-sterile, contaminated, or of unknown concentration, adding infection and overdose risk on top of the compound's intrinsic effects.

Given this profile, the appropriate stance is caution: Melanotan II is not a benign 'tanning shortcut,' and its risks — particularly around pigmented lesions — are taken seriously in the clinical literature.

• nausea and facial flushing (frequently observed in early clinical dosing)
• spontaneous penile erections in male subjects
• darkening and rapid change of existing moles and new melanocytic naevi (raising melanoma-surveillance concerns — reported in dermatology case literature)
• priapism (prolonged, painful erection — reported in case reports, a urological emergency)
• generalized hyperpigmentation, including of lips, gums and skin folds
• risk of unsterile/contaminated product and injection-related infection in the unregulated supply

VII. Frequently Asked Questions