Melanotan II
Melanotan II (MT-II) · Ac-Nle4-Asp5-His6-D-Phe7-Arg8-Trp9-Lys10-NH2 · ~1024 Da
Executive Summary
Melanotan II (MT-II) is a synthetic, cyclic analogue of alpha-melanocyte-stimulating hormone (alpha-MSH) developed in academic research settings, not a licensed cosmetic or prescription medicine for tanning. The best-supported claim is narrow: MT-II can increase visible skin pigmentation in humans, but the peer-reviewed efficacy evidence is extremely small (a pilot phase-I study in three volunteers). Everything beyond "it can darken skin" sits on much weaker ground. Claims that MT-II provides reliable photoprotection or reduces skin-cancer risk are not supported by controlled human outcome data and should be treated as marketing narratives rather than evidence. The safety signal is more concrete than many online sellers admit: controlled human studies report frequent nausea and yawning, and multiple case reports link MT-II exposure with severe harms (rhabdomyolysis/renal dysfunction, priapism requiring urgent care) and concerning pigmentary changes (rapidly changing naevi, eruptive dysplastic naevi, melanoma temporally associated with MT-II use). A second, under-discussed risk layer is product quality: a peer-reviewed forensic analysis of MT-II vials sold illegally online found measurable impurities and inconsistent dose content versus the label claim.
MT-II is a biologically active, systemically acting peptide with limited human efficacy data, no robust long-term safety programme, and real-world evidence of serious adverse outcomes, compounded by unreliable black-market manufacturing. This combination makes cosmetic self-experimentation an indefensible risk-benefit trade. If a product can reliably change your pigmentation via systemic receptor activation, it is pharmacologically active and deserves the same evidence standards as any other drug. MT-II does not meet those standards.
What Melanotan II Is and What It Is Not
MT-II is a lactam-bridged cyclic peptide derived from alpha-MSH fragments. The phase-I clinical paper reports the MT-II structure as Ac-Nle4-Asp5-His6-D-Phe7-Arg8-Trp9-Lys10 alpha-MSH(4-10)-NH2. Mechanistically, MT-II is best described as a non-selective melanocortin receptor agonist: it activates MC1R (skin melanocytes, driving melanogenesis), MC3R/MC4R (CNS energy balance and sexual function circuitry), and potentially other pathways including mast-cell/histamine signalling. A crucial nuance often absent from social media is that not all MT-II effects appear to be mediated solely by canonical melanocortin receptors; in mice, MT-II-induced hypothermia/hypometabolism depended on mast cells and histamine H1 receptors, suggesting off-target physiology that could relate to unexpected reactions in humans.
- It is not an approved medicine for tanning by any major regulatory agency. The FDA, TGA, EMA, HPRA, and Health Canada have all issued warnings or enforcement actions against melanotan products.
- It is not the same compound as afamelanotide (Scenesse), which is an EMA-authorised melanocortin medicine for erythropoietic protoporphyria under controlled specialist use. The existence of that approved drug underscores what MT-II lacks: standardised manufacturing, defined indication, and structured safety follow-up.
- It is not supported by large modern randomised trials with robust dermatologic surveillance, long-term follow-up, or validated tanning/photoprotection endpoints.
- It is not safe because it is 'just a peptide'. Controlled human studies document frequent adverse effects (nausea, yawning, somnolence), potent systemic effects (erections without stimulation), and case reports document serious harms including priapism and rhabdomyolysis.
Mechanism of Action
MC1R activation and melanogenesis
Well-supported biological plausibilityMC1R activation in skin melanocytes increases cAMP signalling and upregulates melanogenic pathways (tyrosinase activity and melanin production). The linkage between melanocortin receptor activation, cAMP, and melanogenesis in human melanocytes is well-supported biologically, even when demonstrated using endogenous melanotropins rather than MT-II specifically. The early medicinal-chemistry and bioassay literature (frog/lizard pigment cell systems and melanoma-cell tyrosinase assays) established that cyclic alpha-MSH fragment analogues, including the structural class that MT-II belongs to, can be superpotent melanotropins in pigmentary bioassays.
Biological plausibility for tanning is clear, but this does not validate cosmetic self-use or establish safety.
MC3R/MC4R central nervous system effects
Supported by animal and human dataMT-II has measurable affinity for MC3R and MC4R and produces behavioural/physiological effects consistent with central melanocortin signalling: reduced food motivation/intake in animal models, and penile erection and increased sexual desire in human trials. Centrally administered MT-II suppressed feeding acutely and modulated neuropeptide-Y-driven hyperphagia in rats. In human studies, MT-II induced erections in a majority of participants without sexual stimulation and increased reported sexual desire versus placebo.
These CNS effects confirm MT-II is a systemically active drug, not a cosmetic. The sexual function effects are pharmacologically potent but come with significant side effects.
Mast-cell activation and histamine signalling
Safety-relevant off-target pathwayIn mice, MT-II-induced hypothermia/hypometabolism depended on mast cells and histamine H1 receptors. Plasma histamine rose after MT-II administration; blocking or deleting histamine H1 signalling attenuated the response. This suggests biologically meaningful off-target physiology (or non-canonical pathways) that could plausibly relate to unexpected reactions in humans such as flushing and systemic symptoms.
This is a safety-relevant biological signal, not a cosmetic benefit. It underscores that MT-II has broader systemic activity than the tanning narrative suggests.
Animal Evidence Map
The preclinical literature contains many positive findings, summarised below with stated limitations.
| Domain | Species | Dose | Outcome | Limitation |
|---|---|---|---|---|
| Thermoregulation and mast-cell activation | Mouse | MT-II i.p. (metabolic study doses) | Profound transient hypothermia/hypometabolism requiring mast cells; plasma histamine rose; blocking or deleting histamine H1 signalling attenuated the response. | Mouse physiology; relevance to human adverse reactions uncertain but safety-relevant. |
| Feeding/adiposity (central administration) | Rat | Central infusion MT-II, 7 days (nmol/day scale) | Acute anorexia; modulated NPY-driven hyperphagia and adiposity. Tolerance/adaptation occurred over the infusion period. | Central administration not comparable to cosmetic dosing; tolerance/adaptation complicates translation to weight-loss claims. |
| Food motivation (nucleus accumbens) | Rat | Nucleus accumbens microinjection | Reduced both appetitive responding and food consumption without producing conditioned taste avoidance. | Highly local CNS manipulation; not a clinical weight-loss evidence base. |
| Stress/depression model | Rat | Systemic MT-II (as ACTH(4-10) analogue) | Attenuated anhedonia markers and affected hippocampal BDNF measures in chronic unpredictable stress paradigm. | Interesting but far from a clinical antidepressant evidence base. |
| Ototoxicity protection (negative finding) | Guinea pig | 30 or 3 ug/kg/day s.c. with cisplatin | No protection against cisplatin ototoxicity at the tested doses. | Negative finding in a specific toxicity model; a reminder that 'melanocortins are broadly protective' is not universally true for MT-II. |
| Melanoma biology (B16-F10 model) | Mouse | Topical MT-II application | A 2020 study reported topical MT-II reduced tumour progression in mice and inhibited migration/invasion in vitro. | Does not establish clinical cancer benefit and should not be misused to claim 'MT-II prevents cancer.' The model addresses tumour behaviour under experimental conditions, not human carcinogenesis risk from systemic tanning use. |
Human Evidence
Every published human study for Melanotan II is reviewed below. None are randomised controlled trials.
Pilot phase-I pigmentation study
Single-blind, alternating day placebo-controlled pilotn=3; short follow-up; male-only; not designed for long-term safety. This is the entire peer-reviewed human efficacy dataset for tanning.
Demonstrates the effect is real but provides virtually no generalisable efficacy or safety data.Erectile dysfunction/sexual motivation study
Controlled clinical trial with RigiScan monitoringSmall clinical study; not a modern drug-development safety package. Demonstrates pharmacologic potency and side effects more than therapeutic readiness.
Confirms potent systemic pharmacology but highlights significant side-effect burden.Hype vs Evidence
Common online claims compared against what the published evidence actually supports.
| Claim | Social Media Implies | Evidence Supports | Verdict |
|---|---|---|---|
| MT-II gives you a sunless tan | Safe, effective, convenient tanning alternative to UV exposure | A tiny phase-I human study observed increased pigmentation in 2 of 3 participants after subcutaneous dosing, objectively measured by reflectance/visual assessment. However, no large modern RCTs exist; outcomes are short-term, small-n, male-only. |
Supported, but limited
|
| MT-II is photoprotective / prevents sunburn | More melanin from MT-II provides UV protection and prevents burns | Mechanistically plausible that more eumelanin can increase UV resistance, but MT-II-specific human photoprotection endpoints are not robustly established in trials. No controlled human trials demonstrating reduced sunburn rates or validated photoprotection endpoints. Behavioural confounding exists (people may stay longer in sun due to false reassurance). |
Unproven
|
| MT-II lowers melanoma risk because melanin protects you | Using MT-II is protective against skin cancer | No controlled human data support melanoma risk reduction. Regulators and clinicians instead warn about concerning pigment changes and potential cancer risk signals. Case reports describe melanoma temporally associated with MT-II; causality uncertain but risk-reduction claims are not evidence-based. |
Contradicted / misleading
|
| It's safe because it's 'just a peptide' | Natural and harmless because peptides are biological molecules | Human studies show frequent adverse effects (nausea, yawning, somnolence at higher doses) and potent systemic effects (erections without stimulation). Serious harms reported: rhabdomyolysis/renal dysfunction and priapism requiring urgent intervention in case reports. |
Misleading
|
| Nasal MT-II works like injections | Nasal spray is an easy, equivalent alternative to subcutaneous injection | Peer-reviewed literature includes concern about nasal spray use and at least one case report framing it as a possible risk factor in oral mucosal melanoma. No clear body of controlled intranasal MT-II trials demonstrating reliable absorption, dose consistency, or safety. |
Unproven / risky
|
| MT-II is accurately dosed and pharmaceutical grade online | Online peptide products are reliable and pure | Chemical analyses of illicit online products show impurities (roughly 4-6% in some vials) and content mismatch ('10 mg'-labelled vials containing substantially less MT-II). No supply-chain assurance, no regulatory batch release, no sterility guarantees. |
False in general
|
Evidence Strength Ratings
Each domain rated on a 0-5 scale based on quality and quantity of available evidence.
Safety, Side Effects & Regulatory Status
Peer-reviewed pharmacokinetic work exists in animals. In rats, MT-II plasma determination methods (HPLC and bioassay) were applied to an IV 0.3 mg/kg study, showing biphasic disposition and method correlation. In humans, rigorous MT-II PK/ADME reporting is sparse in the readily accessible literature; the key early human trials emphasise pharmacodynamic outcomes (pigmentation, erections, side effects) rather than formal plasma PK parameterisation. The frequent online claims of a confidently known human half-life for MT-II should therefore be treated with scepticism unless backed by primary human PK studies.
Controlled human studies report that MT-II commonly produces nausea, yawning/stretching behaviours, and sometimes somnolence/fatigue, consistent with broad melanocortin system activation. Sexual and cardiovascular-autonomic adverse effects are not hypothetical: the controlled ED literature documents erections without sexual stimulation and frequent nausea/yawning; case reports document priapism requiring urgent intervention. Severe toxicity exists in the case literature (rhabdomyolysis and renal dysfunction with sympathomimetic features). Dermatologic risk signals include rapidly changing moles, eruptive dysplastic naevi, and melanoma temporally associated with MT-II use. Additional case reports document intra-oral mucosal pigmentation changes, oral mucosal melanoma as a possible risk factor with nasal spray use, and hypercortisolism/hyperglycaemia/ketosis in a type 1 diabetes patient. The key editorial point is not 'this always happens,' but 'this can happen, and the market that sells MT-II is structurally incapable of offering pharmaceutical-grade quality control or post-marketing surveillance.' A peer-reviewed forensic analysis of MT-II vials sold illegally online found measurable impurities (roughly 4-6% in some vials) and content mismatch ('10 mg'-labelled vials containing substantially less).
Melanotan products marketed in the US are unapproved drugs. Historical enforcement communications document warning letters and classification as an unapproved new drug.
View Official Source →The EMA has authorised afamelanotide (Scenesse) for erythropoietic protoporphyria under controlled specialist use, often confused with melanotan. This approval does not extend to MT-II.
View Official Source →Publicly warned against tanning products containing melanotan and notes serious risks. Advertising compliance reporting describes MT-II as an unapproved prescription medicine being unlawfully promoted.
View Official Source →States Melanotan 2 is not authorised by the HPRA or any medicines regulator, is not a cosmetic, and advises users to stop immediately.
View Official Source →Public advisories naming Melanotan II among unauthorised injectable peptide drugs that may pose serious health risks.
View Official Source →MT-II is prohibited under category S0 (non-approved pharmacological substances) at all times, capturing substances without governmental regulatory approval for human therapeutic use.
View Official Source →What We Still Don't Know
- True long-term melanoma incidence relative to baseline risk, adjusted for UV exposure and sunbed use (unknown; case reports only).
- Long-term cardiovascular/autonomic risk profile under repeated exposure (not established).
- Human pharmacokinetic/ADME parameters under controlled conditions (limited; animal IV PK exists; human PK not well characterised in accessible literature). Online claims of a confidently known human half-life should be treated with scepticism.
- Safety of intranasal formulations (no credible pharmaceutical standardisation; likely high variability).
- Interaction between MT-II-driven melanogenesis and pre-existing pigmented lesion biology in genetically susceptible individuals.
- Whether mast-cell/histamine-mediated effects observed in mice translate to clinically meaningful adverse reactions in humans.
References
All primary sources cited in this review. Links open in new tabs.
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Subcutaneous MT-II pilot phase-I pigmentation studySingle-blind, alternating day placebo-controlled pilot in 3 healthy male volunteers testing escalating subcutaneous MT-II doses. Two subjects showed increased pigmentation; nausea and spontaneous erections observed.
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MT-II erectile function study with RigiScan monitoringControlled clinical trial demonstrating MT-II-induced erections without sexual stimulation and increased sexual desire versus placebo in men with ED; frequent nausea and yawning.
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MT-II hypothermia/hypometabolism mediated by mast cells and histamine H1 receptorsMouse study showing MT-II-induced hypothermia requires mast cells; plasma histamine rose after MT-II; H1 receptor blockade attenuated the response.
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Central MT-II feeding suppression and NPY modulation in ratsCentral infusion of MT-II suppressed feeding acutely and modulated NPY-driven hyperphagia and adiposity over 7-day period in rats.
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MT-II nucleus accumbens microinjection reduces food motivationMT-II delivered to reward circuitry reduced appetitive responding and consumption without conditioned taste avoidance.
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MT-II attenuates anhedonia in chronic unpredictable stress modelSystemic MT-II attenuated anhedonia markers and affected hippocampal BDNF in chronic unpredictable stress paradigm in rats.
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MT-II fails to protect against cisplatin ototoxicity in guinea pigsNegative finding: MT-II at 30 or 3 ug/kg/day did not protect against cisplatin-induced ototoxicity.
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Topical MT-II and B16-F10 melanoma progression in mice2020 study reporting topical MT-II reduced tumour progression in mouse melanoma model and inhibited migration/invasion in vitro.
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Alpha-MSH fragment analogues as superpotent melanotropinsEarly medicinal-chemistry literature establishing cyclic alpha-MSH analogues including MT-II structural class as superpotent melanotropins in frog/lizard pigment cell bioassays.
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Rhabdomyolysis and renal dysfunction after subcutaneous MT-IICase report of systemic toxicity with rhabdomyolysis and renal dysfunction after subcutaneous MT-II purchased online; product analytically confirmed by mass spectrometry.
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Ischaemic priapism associated with MT-II injectionCase report(s) of ischaemic priapism temporally associated with MT-II injection requiring urgent intervention.
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Eruptive dysplastic naevi after MT-II exposureClinical report of rapidly changing moles and eruptive dysplastic naevi in MT-I/MT-II users.
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Forensic analysis of MT-II products sold illegally onlinePeer-reviewed chemical analysis finding unknown impurities (4-6% range) and content mismatch in '10 mg'-labelled MT-II vials.
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MT-II plasma pharmacokinetics in ratsHPLC and bioassay methods applied to IV 0.3 mg/kg MT-II study in rats, showing biphasic disposition and method correlation.
View the compound profile for Melanotan II including dosage forms, administration routes, and category information.
View Compound Profile →Frequently Asked Questions About Melanotan II
Controlled human studies report frequent nausea and yawning. Case reports document serious harms including rhabdomyolysis with renal dysfunction, ischaemic priapism requiring urgent care, rapidly changing naevi, eruptive dysplastic naevi, and melanoma temporally associated with MT-II use. The overall evidence score is 1.5 out of 5.
MT-II carries significant safety signals. It is not approved by any major regulatory agency (FDA, TGA, EMA, Health Canada have all issued warnings). Peer-reviewed forensic analysis of products sold online found measurable impurities and inconsistent dosing. It is a systemically active drug, not a cosmetic.
Multiple case reports link MT-II exposure with concerning pigmentary changes including rapidly changing moles, eruptive dysplastic naevi, and melanoma temporally associated with use. Controlled long-term studies to establish or refute a causal melanoma link do not exist.
MT-II is not approved for tanning by any major regulatory agency. The FDA, TGA, EMA, HPRA, and Health Canada have all issued warnings or enforcement actions against melanotan products. It is prohibited by WADA under S0 (Non-Approved Substances).
MT-II is a non-selective melanocortin receptor agonist. It activates MC1R in skin melanocytes to drive melanogenesis (tanning), and also activates MC3R/MC4R in the CNS affecting appetite and sexual function. It additionally triggers mast-cell activation and histamine signalling, contributing to off-target effects.
Afamelanotide (Scenesse) is an EMA-authorised melanocortin medicine for erythropoietic protoporphyria under controlled specialist use. Unlike MT-II, it has standardised manufacturing, a defined indication, and structured safety follow-up. MT-II lacks all of these.
Reviewed by the Peptide Science Thailand Editorial Team.
Last reviewed: March 1, 2026