Research library
Melanotan II Research Overview: Melanocortin Receptor Pharmacology, Pigmentation Findings and Reported Adverse Signals
- Compiled by:
- Peptide Pilots Scientific Content Team
- Reviewed by:
- Peptide Pilots Quality & Compliance review
- Last revised:
What does published research establish about Melanotan II's melanocortin receptor activity, and what do regulators say about its unsupervised use?
Melanotan II is a cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone that non-selectively activates melanocortin receptors, principally MC1R (pigmentation) and MC4R (central energy-balance and sexual-behaviour pathways). Early clinical-pharmacology studies in the 1990s established that it increases melanin synthesis and reported incidental effects on libido and erectile response, which led to the separate development of the MC4R-selective analogue bremelanotide (PT-141) for sexual-dysfunction indications. Melanotan II itself was not advanced through registration trials and is not an approved drug in any jurisdiction; multiple national medicines regulators have issued public warnings about unregulated products sold under this name, citing reports of pigmented lesions, nausea, hypertension and unknown impurity content.
This page is an educational literature summary for laboratory professionals. It is not medical advice, not a description of product performance, and it does not describe or endorse human or veterinary use. Materials referenced are supplied for controlled laboratory research only.
What is Melanotan II?
Melanotan II is a synthetic, lactam-cyclised heptapeptide analogue of alpha-MSH, engineered for metabolic stability and receptor potency relative to the native tridecapeptide hormone.
In laboratory work it is used as a pharmacological tool for non-selective melanocortin receptor activation, in cAMP-accumulation and receptor-binding assays, and in early-phase human pharmacology studies examining pigmentation and sexual-behaviour endpoints. It is not an approved therapeutic and has no established research-grade clinical use.
Melanotan II names and identifiers
Also referred to as: MT-II; MT-2; melanotan-2
| Peptide sequence | Cyclic: Ac-Nle-cyclo[Asp-His-DPhe-Arg-Trp-Lys]-NH2 |
|---|---|
| Molecular formula | C50H69N15O9 |
| Molecular weight | ≈1024.2 g/mol |
| CAS number | 121062-08-6 |
| Receptor activity | Non-selective agonist across MC1R, MC3R, MC4R and MC5R |
| Regulatory status | Not approved as a drug in the US, EU, UK, Australia or elsewhere; subject to public safety alerts from multiple national regulators |
Melanotan II research background
Melanotan II was synthesised at the University of Arizona in the late 1980s as part of work on stable, cyclic alpha-MSH analogues for potential use as a sunless-tanning and skin-cancer-prevention agent.
Small phase I pharmacology studies in the 1990s reported dose-dependent skin pigmentation and incidentally noted spontaneous erections in male subjects, an observation that motivated separate development of the MC4R-selective fragment bremelanotide, which underwent its own clinical trial programme and was later approved for hypoactive sexual desire disorder under the name Vyleesi.
Melanotan II itself was not carried through registration trials for any indication. Since the 2000s it has circulated as an unregulated research chemical and injectable tanning product, prompting an active body of case-report and regulatory-safety literature distinct from the small formal pharmacology dataset.
Proposed Melanotan II mechanisms and pathways
Evidence is separated by study type. In-vitro and animal findings describe model systems and do not establish equivalent behaviour in humans.
Melanotan II in-vitro and cell-based evidence
- Receptor-binding and cAMP-accumulation assays confirm nanomolar agonist potency at MC1R, MC3R, MC4R and MC5R, with no meaningful receptor subtype selectivity, distinguishing it from later selective analogues.
- MC1R activation in melanocyte culture increases tyrosinase activity and eumelanin production, the basis of its pigmentation effect.
- Because MC4R and MC3R are also engaged, in-vitro pharmacology alone predicts the compound's central appetite and sexual-behaviour effects observed later in vivo, rather than a pigmentation-selective action.
Melanotan II animal-model evidence
- Rodent studies link MC4R activation to reduced food intake and altered energy expenditure, and MC4R agonism is separately implicated in centrally mediated penile erection responses in rat models.
- Pigmentation responses in animal models are consistent with MC1R-driven melanogenesis and were the original basis for pursuing the compound as a sunless-tanning candidate.
Published Melanotan II human-study evidence
- Early phase I studies (Dorr et al.) reported dose-dependent tanning after subcutaneous administration together with nausea as a common adverse effect.
- A subsequent controlled trial in men reported increased erectile responses, motivating the separate clinical development of bremelanotide rather than Melanotan II itself.
- Beyond these early-phase studies, no adequately controlled human efficacy or long-term safety trial has been published; the more extensive human literature that exists is case-report and pharmacovigilance data describing adverse events from unregulated product use, including new or changing pigmented lesions, hypertension, and rhabdomyolysis in isolated reports.
Published Melanotan II studies
| Study | Model / type | Research question | Main observation | Citation |
|---|---|---|---|---|
| Dorr et al., phase I pigmentation study | Human, dose-escalation phase I, subcutaneous administration | Does Melanotan II produce measurable skin pigmentation and what adverse events accompany it? | Reported dose-dependent increases in skin pigmentation with nausea and flushing as common adverse effects. | Life Sciences, 1996 |
| Wessells et al., erectile response study | Human, randomised controlled trial in men with organic erectile dysfunction | Does subcutaneous Melanotan II increase erectile response? | Reported a higher rate of erections versus placebo, a finding that supported subsequent development of the MC4R-selective analogue bremelanotide. | International Journal of Impotence Research, 2000 |
| Receptor pharmacology characterisation | Cell-based cAMP and binding assays across cloned human melanocortin receptors | How selective is Melanotan II across melanocortin receptor subtypes? | Confirmed potent, non-selective activation of MC1R, MC3R, MC4R and MC5R. | Peptides, 2006 |
| National regulatory safety alerts and case series | Pharmacovigilance case reports and regulator communications | What adverse events are reported with unregulated injectable Melanotan II products? | Multiple regulators (including the UK MHRA, Australia's TGA and the US FDA) have issued warnings citing reports of new/changing moles, nausea, hypertension and uncharacterised product content in unregulated supplies. | GOV.UK / MHRA public communications, 2023 |
Limitations of the Melanotan II evidence
- Melanotan II was never carried through full registration trials; the formal controlled human dataset is limited to small, short, early-phase pharmacology studies from the 1990s.
- Because the compound is non-selective across melanocortin receptors, pigmentation, appetite and sexual-behaviour effects are not separable, which is precisely why later development moved to the selective analogue bremelanotide.
- The larger body of human data associated with the name 'Melanotan II' consists of case reports and regulatory pharmacovigilance describing unregulated, non-pharmaceutical-grade products of unverified composition; these reports document harm signals but cannot be used to characterise the pharmacology of the peptide itself.
- No long-term human safety or carcinogenicity data exist; MC1R activation raising concern about melanocytic proliferation (reported changing naevi) is a specific, documented safety signal that remains inadequately studied in controlled settings.
- Multiple national medicines regulators have explicitly warned against use of unregulated Melanotan II products, which should be weighed heavily against any research or personal interest in the compound.
Melanotan II laboratory characteristics
Handling and analytical information reported in the literature and in supplier documentation. Values apply to laboratory materials and are not directions for any other use.
| Appearance | White to off-white lyophilised powder |
|---|---|
| Solubility | Soluble in water and dilute acetic acid |
| Lyophilised storage | Commonly stored at −20 °C, desiccated and protected from light |
| Reconstituted handling | Solutions are typically kept refrigerated and used within a short window due to reported degradation |
| Analytical testing | RP-HPLC purity and MS identity are the standard characterisation methods; independent testing of unregulated commercial products has repeatedly found content and purity discrepancies |
| Stability considerations | Cyclic lactam structure confers greater metabolic stability than native alpha-MSH, but solution stability at room temperature is limited |
Frequently asked Melanotan II research questions
Is Melanotan II an approved medicine?
No. It has not been approved by the FDA, EMA, MHRA or any other major regulator for any indication. The related, receptor-selective compound bremelanotide (PT-141) is separately approved in the US for one indication.
Why do regulators warn against Melanotan II specifically?
Public health agencies have issued alerts describing reports of new or changing pigmented skin lesions, nausea, hypertension and uncertain product composition in unregulated supplies sold as Melanotan II.
Is Melanotan II the same as PT-141/bremelanotide?
No. Both are melanocortin receptor agonists derived from alpha-MSH, but Melanotan II is non-selective across MC1R–MC5R, whereas bremelanotide was engineered for greater MC4R selectivity and underwent its own separate clinical development programme.
What is the strongest documented human evidence available?
Small phase I dose-escalation and pharmacology studies from the 1990s reporting pigmentation and erectile-response endpoints; these are limited in size and duration and do not constitute a modern controlled efficacy or safety trial.
Melanotan II primary references
- Dorr RT, Lines R, Levine N, et al. (1996). Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sciences. https://doi.org/10.1016/0024-3205(96)00135-3
- Wessells H, Levine N, Hadley ME, Dorr R, Hruby V (2000). Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with melanotan II. International Journal of Impotence Research. https://doi.org/10.1038/sj.ijir.3900496
- Hadley ME, Dorr RT (2006). Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides. https://doi.org/10.1016/j.peptides.2005.01.026
- UK Medicines and Healthcare products Regulatory Agency (2023). Melanotan safety warning: injectable tanning products. GOV.UK / MHRA public communications. https://www.gov.uk/government/news/melanotan-illegal-unlicensed-tanning-jabs-warning
Authorship and revision
Compiled from primary literature and public databases. Every factual statement on this page is traceable to a listed reference. Compiled by Peptide Pilots Scientific Content Team; documentation and compliance review by Peptide Pilots Quality & Compliance review. First published ; last revised . Pages are revised when the cited literature changes materially.
Catalogue reference
Peptide Pilots supplies Melanotan 2 as a laboratory reagent with per-lot RP-HPLC and mass-spectrometry documentation. Quantities, testing, packaging and fulfilment details are on the catalogue page.
Related catalogue products
Laboratory reagents supplied by Peptide Pilots from the Reproductive & Sexual-Health Research tier. Research use only; not for human or veterinary use.
