Melanotan II · pigment, receptors and human evidence
Melanotan II is a synthetic, seven-residue peptide that activates several melanocortin receptors. It can stimulate pigmentation, and small human experiments also recorded erections and nausea. Those effects explain the interest in it; they do not establish a safe tanning treatment. Melanotan II is a different molecule from Melanotan I and PT-141, and it has no FDA-approved finished drug.
Does it actually work? A 1996 pilot observed increased pigmentation in two of three men. That is a real human observation, but an extremely small basis for predicting results, choosing a regimen or judging long-term harm. The most useful question is what each study measured—and what it left unanswered. Read the original pilot.
Melanotan II at a glance
What it is
A cyclic analogue of the α-MSH hormone’s 4–10 region. The seven residues include a side-chain ring and a D-phenylalanine residue.
What has been observed
Pigmentation in a three-person pilot; erections in small controlled studies; extensive receptor and animal experiments.
What remains uncertain
A reliable tanning timeline, long-term benefit–risk balance, cancer incidence and the safety of retail sprays or vials.
“Melanotan,” “MT-II” and “MT2” are common search terms, but the numeral matters. A result for afamelanotide, bremelanotide or another melanocortin agonist should not be presented as a Melanotan II result.
What did the human Melanotan II studies find?
The early studies were small, but they were not all the same experiment. Separating their participants, comparators and measurements prevents both exaggerating and dismissing the evidence.
Pigmentation pilot · 1996
Two had increased pigmentation recorded visually and by quantitative reflectance one week after the treatment period. The single-blind study alternated MT-II and saline days. It also reported nausea, yawning, stretching, erections, and somnolence/fatigue at a higher studied level. Dorr et al.
Psychogenic ED · 1998
In a double-blind crossover, eight developed clinically apparent erections on MT-II. Mean duration of tip rigidity above 80% was 38 minutes versus three with placebo, P=.0045. This was an instrument-measured response, not proof of an approved treatment. Wessells et al.
Organic ED · 2000
A separate crossover reported erections after 12 of 19 MT-II administrations versus one of 21 placebo administrations. These are administration counts, not 40 participants. Severe nausea occurred after four of the 19 MT-II administrations. Wessells et al.
A 2000 review from the same group summarizes experience in 20 men with psychogenic or organic erectile dysfunction. It should not be added to the two ten-person studies as another independent 20-person trial. Its desire responses were also reported per administration, a distinction lost when dose counts are relabeled as people.
These studies demonstrate biological activity under their specific conditions. They do not validate cosmetic self-use, sexual-performance claims for everyone, nasal delivery, a preferred commercial preparation or long-term safety. Their short observation windows are especially weak evidence about uncommon or delayed harm.
Melanotan I vs Melanotan II vs PT-141
They share a research history and some receptor biology. They are not three strengths of the same substance.
| Molecule | Structural distinction | Relevant evidence and approval |
|---|---|---|
| Melanotan II | Cyclic seven-residue peptide; Asp–Lys side-chain lactam; terminal amide. | Small early pigmentation and sexual-function studies. No FDA-approved Melanotan II finished drug. |
| Melanotan I / afamelanotide | Linear 13-residue α-MSH analogue, with Nle and D-Phe substitutions. Its label describes predominantly MC1R binding, not absolute MC1R exclusivity. | Scenesse is a defined implant approved for increasing pain-free light exposure in adults with a history of phototoxic reactions from erythropoietic protoporphyria. |
| PT-141 / bremelanotide | Related cyclic seven-residue peptide with a terminal free acid instead of MT-II’s terminal amide. | Vyleesi has a specific indication in premenopausal women with acquired, generalized hypoactive sexual desire disorder. It is not a general sexual-performance enhancer. |
On a narrow screen, scroll the table horizontally. Sources: current Scenesse label, Vyleesi label, and the MT-II pilot.
A vial or nasal spray labeled “Melanotan I” does not inherit Scenesse’s manufacturing, delivery system or clinical evidence. Nor does overlapping receptor activity make Melanotan II interchangeable with bremelanotide. For the fuller molecule-specific records, see the Melanotan I guide and PT-141 guide.
What is the Melanotan II molecule?
The sequence is commonly written Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-NH₂. The ring joins the Asp side-chain carboxyl to the Lys side-chain amine; it is not an end-to-end circle through all seven residues. The Nle residue sits outside that side-chain ring. The acetyl group and terminal amide are also part of the identity. Original clinical structure · cyclic-analogue receptor study.
Seven residues, with a six-residue segment inside the bridge
Asp side chain ↔ Lys side chain: lactam connection. The boxes identify sequence positions; they are not a molecular conformation or atom-level structure.
PubChem CID 92432 gives the parent formula C₅₀H₆₉N₁₅O₉ and average molecular weight about 1,024.2 g/mol. That average mass is different from a monoisotopic mass or a charged ion’s m/z. Associated acetate, water and other formulation components must be considered separately when interpreting a material’s measured amount.
Why can a tanning-related peptide affect appetite and sexual function?
Melanotan II activates multiple receptor subtypes. Human receptor assays support activity at MC1R, MC3R, MC4R and MC5R. “Nonselective” means activity across several targets; it does not mean identical potency, exposure or effects at each one.
Pigmentation-related signaling in melanocytes.
Part of central melanocortin circuitry associated with energy regulation.
Central and autonomic pathways relevant to feeding and sexual responses.
A distinct subtype with tissue-dependent functions; binding alone is not a clinical benefit.
MC2R is the important exception: it is the ACTH receptor and is outside the established MT-II agonist set. The foundational MSH/ACTH receptor cloning, MC3R cloning, human MC4R work, rat-brain MC4R distribution and mouse MC5R study explain why these are separate biological targets, not a single “tanning receptor” in different locations.
Even that receptor map does not explain every observation. In a 2018 mouse study, MT-II-induced hypothermia persisted when individual melanocortin receptors were absent. Mast cells and histamine H1 signaling were important instead. This is a mechanistic caution from mice, not evidence that every human reaction follows that pathway.
Does it help with fat loss?
Reduced appetite is not the same as sustained, beneficial fat loss. Rat hypothalamic experiments found reduced feeding without taste aversion under one localized administration design. A separate rat study found food suppression accompanied by aversive effects under its acute and chronic paradigms. The findings depend on the model and method.
In Siberian hamsters, MT-II reduced short-term feeding and increased grooming, but the similar response across seasonal states did not explain seasonal weight change. These are useful research observations; they do not establish a human weight-management treatment.
How long does Melanotan II take to work—and last?
Blood concentration
A pharmacokinetic measurement asks how much peptide is detected over time. The reviewed rat and mouse studies cannot supply a reliable human “one-to-two-hour” half-life for a retail preparation.
Visible pigmentation
A pigment change can remain after the initiating signal has changed. In the three-person pilot, pigmentation was assessed one week after treatment ended. That is an observation time, not a proven onset time or a permanence estimate.
The 1994 rat pharmacokinetic paper is unusually instructive: HPLC and bioassay profiles broadly agreed, yet half-life estimates differed, and the authors explained how sparse late samples could influence them. Later rat mass-spectrometry work and mouse plasma/brain measurements improved analytical detection. Neither makes a human clearance number interchangeable with a tanning timeline.
A 2026 oral-pigmentation case reported that cheek-mucosa discoloration improved after cessation while some gingival pigmentation persisted at three months. Pre-existing pigmentation, smoking and sunbed use complicated attribution. It is not evidence that a tan—or an eye-color change—is permanent.
No controlled eye-color outcome was identified in the scoped literature reviewed here. A before-and-after photograph cannot isolate the peptide from lighting, UV exposure, baseline pigmentation and other exposures.
What side effects and cancer concerns are documented?
The early human studies recorded nausea, yawning, stretching, appetite reduction and erections; the pilot also described somnolence and fatigue. Small studies cannot estimate how frequently serious events occur across broader use.
A 2012 toxicology report documented severe systemic illness, muscle breakdown and renal dysfunction after self-administered internet-purchased material; mass spectrometry confirmed Melanotan II. A 2021 case described a prolonged painful erection requiring surgery, with persistent erectile dysfunction at follow-up. Prior tolerated use did not prevent the later event. A painful erection lasting four hours or more needs urgent medical assessment.
Human melanoma reports
A 2014 case involved both MT-II and sunbed exposure. A 2025 report described oral mucosal melanoma after reported nasal-spray use. These are concerning associations, not controlled estimates of cause or incidence.
A 2026 report of five melanomas in situ also involved tanning beds, MT-II followed by MT-I, numerous atypical nevi and testosterone exposure. The authors explicitly noted that lesions might have pre-existed and become noticeable after darkening.
A different result in mice
A 2020 laboratory study found that topical MT-II slowed growth of established B16-F10 melanoma in mice, with six animals per group and associated MC1R/PTEN signaling. The cell work did not show a general reduction in proliferation.
The experiment studied established tumors under specific laboratory conditions. It did not test whether MT-II initiates melanoma or prevents human cancer. Its positive result does not cancel the human safety reports.
The evidence does not justify either “proven to cause melanoma in everyone” or “protects against melanoma.” Case reports lack the comparison groups and exposure verification needed for incidence estimates. A transplanted mouse tumor is a different question from long-term cosmetic exposure in humans.
MC1R biology also varies by genotype. Human genetics research and melanocyte experiments with α-MSH and ACTH help explain pigment responses and UV sensitivity. They do not establish an MT-II cancer-prevention effect or guarantee that a particular skin type will respond safely.
Does darker skin mean protection from the sun?
No reliable sun-protection claim follows from the small MT-II pilot. Some frequently repeated UV-tanning results come from Melanotan I studies, not Melanotan II. The TGA’s current warning states that artificially increased pigmentation does not protect against UV exposure like suitable sunscreen. It also warns about nasal sprays; avoiding a needle does not demonstrate that a formulation is safe.
Is Melanotan II approved, and is research still active?
Melanotan II has no FDA-approved finished drug. The FDA’s current compounding safety page identifies potential aggregation, peptide-impurity and immunogenicity concerns, and published serious adverse-event reports. A substance identifier or a trial registration is not marketing approval. These sources were checked on September 9, 2026.
The registry search returned NCT07437560, a sponsor-submitted phase 2 vitiligo record marked recruiting with an estimated 60 participants and no posted results. Its own description calls it an “example” study. That unresolved wording prevents treating the entry as independent confirmation that a real program is recruiting. It also cannot support efficacy, approval or a completed 60-person trial.
What can an analytical report establish?
A 2015 analysis of samples from three online shops found 4.32–8.84 mg in vials labeled 10 mg, with differing impurity results. This measured sample set is a reason to examine documentation; it does not describe every supplier or today’s Apex material. Later forensic work used high-resolution mass spectrometry to distinguish MT-II and bremelanotide in confiscated samples.
Chromatographic purity
99.936%Integrated detector area in the Apex APX-2026-0530-M report. This is not the percentage of the entire vial’s mass that is peptide.
Measured active amount
10.0067 mgPer vial in the same report, assessed separately against its 9.8–10.2 mg criterion. Amount, chromatographic purity and molecular identity answer different questions.
That report also distinguishes the lactam/terminal-form identity, residue-specific chirality, unknown peaks and receptor-response measurements. Read each result under its named method. Analytical findings do not make the material an approved medicine or establish a safe human regimen. Match the applicable lot and configuration; a public report does not by itself identify the lot currently shipping.
For qualified laboratory procurement, use the Melanotan II research-material page for current offered material and report links. The COA interpretation guide explains why an identity result, an area percentage and a measured amount must stay separate.
Where did Melanotan II come from?
The University of Arizona melanocortin program developed related analogues over several decades. The differences between them matter more than the idea of one ever-stronger “tanning peptide.”
- 1980 · linear precursor chemistry. Sawyer and colleagues described the Nle/D-Phe-modified linear α-MSH analogue. A roughly 26-fold mouse-cell enzyme result belongs to that assay and molecule, not a human MT-II tanning multiplier.
- 1982 · a different cyclic analogue. The half-Cys4/half-Cys10 study reported very large frog-skin responses and different lizard/mouse results. Its disulfide-linked molecule was not MT-II’s lactam-bridged heptapeptide.
- 1990s onward · MT-I and MT-II development. The 1998 discovery review and 2006 historical synthesis trace the programme. Their historical development descriptions do not supply current approvals or outcomes for every related compound.
Frequently Asked Questions About Melanotan II
What is Melanotan II?
Melanotan II is a synthetic cyclic seven-residue analogue of the alpha-MSH hormone’s 4–10 region. It activates multiple melanocortin receptors and is different from Melanotan I and bremelanotide. It has no FDA-approved finished drug.
Does Melanotan II work without sun exposure?
The small 1996 pilot recorded increased pigmentation in two of three men; the effect was not evidence of a safe tanning regimen or UV protection. Results from separate Melanotan I studies should not be relabeled as Melanotan II evidence. Artificially increased pigmentation does not replace suitable sun protection.
How long does Melanotan II last in the body?
The reviewed rat and mouse pharmacokinetic studies do not establish a reliable human half-life for retail preparations. A peptide’s blood concentration, duration of a receptor response and persistence of pigmentation are different measurements.
Can a Melanotan II tan be permanent?
The small human studies do not establish permanence. A 2026 case reported persistent but reduced gingival pigmentation three months after cessation, with other exposures and pre-existing pigmentation complicating attribution. That is not a controlled estimate of how long a skin tan lasts.
Does Melanotan II make eyes darker?
No controlled eye-color outcome was identified in the scoped literature reviewed for this guide. Skin or oral-mucosa pigmentation cannot establish a predictable or safe iris-color change.
What is the difference between Melanotan I and II?
Melanotan I, also called afamelanotide, is a linear 13-residue peptide. Melanotan II is a cyclic seven-residue peptide. The approved Scenesse implant contains afamelanotide; a research vial or nasal spray does not inherit that finished medicine’s formulation, evidence or approval.
Is Melanotan II the same as PT-141?
No. Bremelanotide, commonly called PT-141, is a related cyclic peptide with a terminal free acid, while Melanotan II has a terminal amide. Vyleesi’s specific approval and clinical evidence do not transfer to Melanotan II.
Does Melanotan II cause cancer?
Melanoma has been reported after exposure, but case reports cannot establish causation or a cancer rate and some include substantial UV or other exposures. A mouse study reporting slower growth of established melanoma does not prove cancer prevention in humans. The long-term risk remains unresolved.
Are Melanotan II nasal sprays safer than injections?
A needle-free route does not establish safety. A published case describes oral mucosal melanoma after reported nasal-spray use, without proving causation, and regulators warn about tanning sprays as well as injections. Comparative safety and reliable retail formulation quality have not been established by the evidence reviewed here.
Is Melanotan II FDA approved?
No. It has no FDA-approved finished drug. FDA identifies potential peptide-impurity, aggregation and immunogenicity concerns and serious published adverse-event reports. Substance identifiers and trial registrations are not marketing approvals.
References and source notes
These sources include small human experiments, receptor studies, animal models, reviews and case reports. They are not a count of independent successful human trials. Current labels, regulator statements and the qualified registry entry are linked beside the relevant discussion.
- Mountjoy KG et al. The cloning of a family of genes that encode the melanocortin receptors. Science (New York, N.Y.). 1992. PMID 1325670.
- Sawyer TK et al. [half-Cys4,half-Cys10]-alpha-Melanocyte-stimulating hormone: a cyclic alpha-melanotropin exhibiting superagonist biological activity. Proceedings of the National Academy of Sciences of the United States of America. 1982. PMID 6281785.
- Sawyer TK et al. 4-Norleucine, 7-D-phenylalanine-alpha-melanocyte-stimulating hormone: a highly potent alpha-melanotropin with ultralong biological activity. Proceedings of the National Academy of Sciences of the United States of America. 1980. PMID 6777774.
- Mountjoy KG et al. Localization of the melanocortin-4 receptor (MC4-R) in neuroendocrine and autonomic control circuits in the brain. Molecular endocrinology (Baltimore, Md.). 1994. PMID 7854347.
- Ugwu SO et al. A comparison of HPLC and bioassay methods for plasma melanotan-II (MT-II) determination: application to a pharmacokinetic study in rats. Biopharmaceutics & drug disposition. 1994. PMID 7981427.
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- Schiöth HB et al. Selectivity of cyclic [D-Nal7] and [D-Phe7] substituted MSH analogues for the melanocortin receptor subtypes. Peptides. 1997. PMID 9357059.
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- Wirth MM et al. Paraventricular hypothalamic alpha-melanocyte-stimulating hormone and MTII reduce feeding without causing aversive effects. Peptides. 2001. PMID 11179607.
- Schuhler S et al. Decrease of food intake by MC4-R agonist MTII in Siberian hamsters in long and short photoperiods. American journal of physiology. Regulatory, integrative and comparative physiology. 2003. PMID 12388479.
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- Breindahl T et al. Identification and characterization by LC-UV-MS/MS of melanotan II skin-tanning products sold illegally on the Internet. Drug testing and analysis. 2015. PMID 24771717.
- Jain S et al. Melanotan II causes hypothermia in mice by activation of mast cells and stimulation of histamine 1 receptors. American journal of physiology. Endocrinology and metabolism. 2018. PMID 29812984.
- Wu JC et al. Topical MTII Therapy Suppresses Melanoma Through PTEN Upregulation and Cyclooxygenase II Inhibition. International journal of molecular sciences. 2020. PMID 31968661.
- Mestria S et al. LC-HRMS characterization of the skin pigmentation and sexual enhancers melanotan II and bremelanotide sold on the black market of performance and image enhancing drugs. Drug testing and analysis. 2021. PMID 33245851.
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- Yassin Alsabbagh A et al. Melanotan II nasal spray: a possible risk factor for oral mucosal malignant melanoma? International journal of oral and maxillofacial surgery. 2025. PMID 40210573.
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