MT-2 (Melanotan II) — Research Overview
Chemical Name: [Nle4, D-Phe7]-alpha-MSH cyclo(5-10) — Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 Also Known As: MT-2, Melanotan II, Melanotan-2, MTII Structure: Synthetic cyclic heptapeptide (7 amino acids in a cyclic ring via a lactam bridge) — a truncated and cyclized analog of alpha-melanocyte-stimulating hormone. The cyclic structure confers resistance to enzymatic degradation compared to linear alpha-MSH, but the truncation and cyclization also fundamentally alter receptor selectivity compared to MT-1 (afamelanotide). Molecular Weight: Approximately 1024 daltons Relationship to MT-1: MT-1 (afamelanotide) is a linear tridecapeptide (13 amino acids) retaining the full alpha-MSH sequence with two stability-enhancing substitutions, with relative MC1R selectivity. MT-2 is a cyclic heptapeptide truncation that does not retain MC1R selectivity — it activates MC1R, MC3R, MC4R, and MC5R with broadly similar affinity, producing a multi-receptor pharmacological profile that MT-1 does not. Regulatory Status: Not approved by the FDA, EMA, or any major regulatory authority for any indication. Prohibited by WADA under S2. No regulatory approval pathway currently exists for MT-2. The Australian TGA reclassified MT-2 as a Schedule 9 prohibited substance in February 2026. Relationship to PT-141 (Bremelanotide): PT-141 (bremelanotide, FDA-approved 2019 as Vyleesi for HSDD in premenopausal women) is a cyclic heptapeptide deaminated metabolite of MT-2, developed specifically to harness the MC4R-mediated sexual function effects observed with MT-2 while improving on its pharmacokinetic and safety profile. PT-141’s clinical development was directly catalyzed by the erectogenic findings observed in MT-2 human trials. Discovery of Erectogenic Activity: The sexual function effects of MT-2 were first documented as an unexpected adverse event in early tanning trials at the University of Arizona in the 1990s — one of the most scientifically consequential serendipitous findings in reproductive pharmacology. WADA Status: Prohibited substance under S2 (peptide hormones, growth factors, related substances, and mimetics) Category: Non-selective melanocortin receptor agonist / multi-receptor alpha-MSH analog / melanogenesis inducer / MC4R-mediated erectogenic agent / research compound (no regulatory approval)
Research Use Only — Disclaimer and Important Safety Context
The scientific literature on this page is provided strictly for educational and informational purposes. All Rogue Compounds products are intended for in-vitro laboratory research use only and are not approved by the FDA for human or animal consumption. The studies referenced below are independent third-party peer-reviewed publications.
Unlike MT-1 (afamelanotide), MT-2 has no approved clinical indication in any jurisdiction, has not completed the Phase 3 clinical development programs that would establish a favorable risk-benefit profile for therapeutic use, and is associated in the published medical literature with documented melanoma case reports in individuals who self-administered it. Researchers are responsible for compliance with all applicable local, state, and federal regulations.
Rogue Compounds makes no claims that any product diagnoses, treats, cures, or prevents any disease or condition.
What Is MT-2 (Melanotan II)?
MT-2 is a synthetic cyclic heptapeptide developed at the University of Arizona in the 1980s by Victor Hruby, Mac Hadley, and colleagues — initially as a companion to MT-1 in the search for pharmacological tools to study the melanocortin system and to develop sunless tanning agents. Where MT-1 preserved the linear tridecapeptide structure of alpha-MSH with two stabilizing substitutions, MT-2 took a structurally more radical approach: truncating the molecule to 7 amino acids and cyclizing it via a lactam bridge between the aspartic acid and lysine side chains. This cyclization was intended to enhance metabolic stability and potency.
The structural approach succeeded in creating a potent melanocortin receptor agonist, but produced a critically different pharmacological profile from MT-1: MT-2 lost the relative MC1R selectivity of MT-1 and became a broad non-selective agonist at MC1R, MC3R, MC4R, and MC5R. This non-selectivity defines MT-2’s research significance and its safety profile in equal measure. The MC1R activity produces tanning and melanogenesis — the intended effect. The MC4R activity in the central nervous system produces spontaneous penile erections, sexual arousal, and appetite suppression — effects that were entirely unexpected when first observed in tanning trials and that subsequently redirected the research trajectory of the entire melanocortin field toward sexual dysfunction therapeutics.
MT-2 has never received regulatory approval in any jurisdiction. The clinical research conducted with MT-2 in the 1990s and early 2000s served primarily as proof-of-concept data that catalyzed development of its metabolite PT-141 (bremelanotide) — which did complete the clinical development pathway and received FDA approval in 2019 for hypoactive sexual desire disorder in premenopausal women. MT-2 itself has remained an unregulated research compound with a safety profile characterized by documented case reports of melanoma in self-administering individuals.
The Melanocortin Receptor Family and MT-2’s Multi-Receptor Profile
The melanocortin receptor family consists of five subtypes (MC1R through MC5R), each with distinct tissue distribution and biological functions.
MC1R — expressed predominantly on melanocytes in skin and hair follicles, with additional expression in keratinocytes, fibroblasts, and immune cells. The primary receptor regulating eumelanin synthesis, photoprotection, and skin pigmentation. Also involved in anti-inflammatory signaling, DNA repair enhancement, and antioxidant defense.
MC2R — the ACTH receptor in the adrenal cortex, driving cortisol biosynthesis. MT-2 does not meaningfully bind MC2R.
MC3R — expressed primarily in the CNS (hypothalamus, limbic system) and in immune cells. Involved in energy homeostasis, appetite regulation, inflammatory modulation, and sexual arousal circuits. MC3R appears to mediate aspects of sexual motivation and timing of maturation.
MC4R — expressed abundantly in the CNS including the hypothalamus, spinal cord, and multiple brain regions. The primary mediator of appetite suppression and energy homeostasis through the POMC/AgRP antagonism. Also expressed at lumbosacral spinal cord levels where it mediates pro-erectile neural signaling through the nitrergic pathway. MC4R activation by MT-2 is the mechanism responsible for both the spontaneous erections and the appetite suppression documented in human trials.
MC5R — expressed in exocrine glands including sebaceous glands, lacrimal glands, and other secretory tissues. Involved in regulation of sebaceous gland activity and exocrine secretion.
MT-2’s non-selective binding across four of these five receptor subtypes explains its complete pharmacological profile and distinguishes it mechanistically from MT-1 (which retains relative MC1R selectivity) and from PT-141/bremelanotide (which was specifically developed to harness MC3R/MC4R activity for sexual dysfunction treatment).
Mechanism of Action
MC1R agonism — melanogenesis: MT-2 binding to MC1R on melanocytes activates Gs-coupled cAMP signaling through adenylyl cyclase, elevating intracellular cAMP and activating protein kinase A. PKA activates the melanogenic transcription factor MITF, which drives expression of tyrosinase and other melanogenic enzymes, leading to eumelanin synthesis and skin darkening. This mechanism is identical to MT-1 but less receptor-selective, as MC3R, MC4R, and MC5R are co-activated at the same doses.
MC4R agonism — pro-erectile and sexual arousal effects: MC4R receptors in the hypothalamic paraventricular nucleus (PVN), other hypothalamic regions, and lumbosacral spinal cord mediate pro-erectile signaling when activated by MT-2. The proposed mechanism involves MC4R activation in the hypothalamus driving oxytocin release from the PVN, which in turn activates nitrergic neurons in the lumbosacral spinal cord that project to the corpus cavernosum. These nitrergic neurons release nitric oxide, which activates guanylyl cyclase in penile smooth muscle, producing relaxation and engorgement through a pathway that is distinct from and additive to the PDE5/cGMP pathway targeted by sildenafil and related PDE5 inhibitors. MT-2-induced erections are spontaneous (not dependent on sexual stimulation), distinguishing them mechanistically from PDE5 inhibitor-facilitated erections that require sexual stimulation as a prerequisite.
MC3R agonism — appetite suppression and energy regulation: MC3R and MC4R co-activation in the hypothalamic arcuate nucleus and paraventricular nucleus suppresses appetite and increases energy expenditure through pathways overlapping with the endogenous POMC-AgRP melanocortin energy balance system. The appetite suppression observed in MT-2 trials is a consequence of this hypothalamic MC3R/MC4R engagement.
MC5R agonism — exocrine effects: MC5R activation in sebaceous and other exocrine glands may contribute to secondary effects on sebaceous secretion, though this receptor’s contribution to MT-2’s clinical pharmacological profile is less well characterized than the other receptor subtypes.
The Serendipitous Discovery of MT-2’s Erectogenic Effects
The discovery that MT-2 produces spontaneous penile erections is one of the most scientifically consequential serendipitous findings in modern pharmacology and provides the essential context for understanding MT-2’s place in melanocortin research history.
In early Phase 1 tanning trials at the University of Arizona, healthy male volunteers receiving MT-2 for its intended purpose of melanogenesis induction reported an unexpected adverse effect: spontaneous penile erections occurring 1 to 5 hours after injection, accompanied by a characteristic stretching and yawning complex. This constellation of effects — erection, stretching, and yawning — had previously been documented as characteristic of opioid receptor activation but was entirely unexpected for a melanocortin peptide. The finding was initially documented as an adverse event in the 1996 Dorr et al. Phase 1 publication.
Rather than simply cataloging this as an unwanted side effect, the Arizona research group recognized its profound therapeutic implications. The observation that a peptide could produce spontaneous erections through a CNS mechanism entirely different from the vascular pathway of PDE5 inhibitors potentially opened a new class of treatment for erectile dysfunction — particularly for the estimated 30-40% of ED patients who are PDE5 inhibitor non-responders due to insufficient endogenous NO production or other peripheral vascular factors. This recognition led directly to the controlled clinical trials of MT-2 for erectile dysfunction, and subsequently to the development of PT-141 (bremelanotide) as a refined analog specifically targeting the sexual function application.
Published Research
Study 1 — Phase 1 Clinical Study: First Human Data on MT-2 Safety, Pharmacokinetics, and Unexpected Erectogenic Effect
Authors: Dorr RT, Lines R, Levine N, Brooks C, Xiang L, Hruby VJ, Hadley ME (University of Arizona) Year: 1996 Journal: Life Sciences PMID: 8637402 Full text: https://pubmed.ncbi.nlm.nih.gov/8637402/
This pilot Phase 1 study was the first published human clinical investigation of MT-2, evaluating its safety, pharmacokinetics, and melanogenic effects — and making the serendipitous observation that would redirect melanocortin research toward sexual dysfunction therapeutics.
MT-2 was evaluated in healthy male volunteers at low doses. Tanning was documented as the expected primary effect, with skin darkening observed within 5-7 days.
Spontaneous penile erections were documented as unexpected adverse events, occurring 1 to 5 hours after injection and accompanied by a characteristic stretching and yawning complex. This adverse event observation was the first published documentation of MT-2’s erectogenic activity in humans.
The pharmacokinetic and safety data from this study established the foundation for subsequent controlled clinical investigation of MT-2’s erectogenic properties and informed dose selection for the Wessells et al. studies that followed.
Study 2 — Controlled Trial: MT-2 Initiates Erections in Psychogenic Erectile Dysfunction (Journal of Urology)
Authors: Wessells H, Fuciarelli K, Hansen J, Hadley ME, Hruby VJ, Dorr R, Levine N (University of Arizona) Year: 1998 Journal: Journal of Urology PMID: 9679884 Full text referenced via: https://www.auajournals.org/doi/10.1016/S0022-5347(01)62903-3
This double-blind placebo-controlled crossover study in 10 men with psychogenic erectile dysfunction was the first controlled human trial directly evaluating MT-2 as an erectogenic agent and the study that catalyzed the entire melanocortin sexual dysfunction therapeutic field.
Ten men with erectile dysfunction of no known organic cause received subcutaneous doses of MT-2 ranging from 0.025 to 0.157 mg/kg or saline vehicle placebo in a crossover design. Real-time RigiScan monitoring documented erection rigidity over a 6-hour post-injection period without sexual stimulation.
Eight of the 10 subjects treated with MT-2 developed clinically apparent erections with greater than 80% rigidity. The mean duration of tip rigidity greater than 80% was 38 minutes with MT-2 and only 3 minutes with placebo (P equal to 0.0045).
The mean time to onset of the first erection was approximately 2 hours from injection (range 15 to 270 minutes). The erections were spontaneous — occurring without sexual stimulation or visual erotic material — confirming a central rather than peripheral mechanism.
Side effects including nausea, stretching, yawning, and decreased appetite were dose-dependent and more frequent with MT-2 than placebo. At the preferred dose of 0.025 mg/kg, side effects were described as mild.
The authors concluded that MT-2 safely initiates erections in men with psychogenic erectile dysfunction through central melanocortinergic mechanisms — the first controlled proof-of-concept for melanocortin receptor agonism as a therapeutic approach to ED.
Study 3 — Extended Controlled Trial: MT-2 Erectogenic Properties in Organic Erectile Dysfunction
Authors: Wessells H, Gralnek D, Dorr R, Hruby VJ, Hadley ME, Levine N (University of Arizona) Year: 2000 Journal: Urology PMID: 11018622 Full text: https://pubmed.ncbi.nlm.nih.gov/11018622/
This study extended the MT-2 erectile dysfunction investigation to men with organic ED risk factors — a clinically more challenging and more representative patient population than psychogenic ED alone — and further characterized the sexual desire effects.
Ten men with an average of 2.2 organic causes for erectile dysfunction were enrolled in a double-blind placebo-controlled crossover study. MT-2 at 0.025 mg/kg and vehicle were each administered twice by subcutaneous injection; RigiScan monitoring and a visual analog scale were used to quantify erections and sexual desire over a 6-hour period.
MT-2 initiated subjectively reported erections in 12 of 19 drug injections versus only 1 of 21 placebo injections. The mean rigidity score of responders was 6.9 on a scale of 0 to 10. Mean duration of tip rigidity greater than 80% was 45 minutes with MT-2 compared to 2 minutes for placebo.
Importantly, increased sexual desire was reported after 10 of the drug injections — the first human controlled evidence that melanocortin receptor agonism affects sexual desire, not just erectile function. The authors noted this finding warrants further investigation of centrally acting agents on disorders of sexual desire, directly foreshadowing the subsequent development of melanocortin-based treatments for HSDD in women.
The authors concluded that the erectogenic properties of MT-2 are not limited to psychogenic ED — men with organic risk factors including hypertension, diabetes, hypogonadism, and other contributing factors developed penile erections after MT-2 administration.
Study 4 — MT-2 to PT-141 Development: The Melanocortin Research Lineage
Authors: Wessells H, Vanderah T (University of Washington and Arizona) Year: 2004 Journal: Current Medicinal Chemistry and multiple publications Referenced via: https://pmc.ncbi.nlm.nih.gov/articles/PMC2694735/
The mechanistic and therapeutic lineage from MT-2 to PT-141 (bremelanotide) represents one of the clearest examples in modern pharmacology of how a serendipitous observation from an unintended effect becomes a licensed therapy.
PT-141 (bremelanotide) is the cyclic heptapeptide deaminated metabolite of MT-2 — structurally closely related but with pharmacokinetic and selectivity properties refined for the sexual dysfunction application. PT-141 was developed specifically to capture MT-2’s MC4R-mediated pro-erectile activity while improving on MT-2’s tolerability profile.
MT-2 induced penile erection via both brain and spinal melanocortin receptors — confirmed through intracerebral injection studies showing that very low doses of MT-2 administered directly to the paraventricular nucleus and lumbosacral spinal cord recapitulated the erectogenic effects of systemic administration, establishing the central neural mechanism as the operative pathway.
PT-141 administered intranasally at doses from 4 to 20 mg produced statistically significant increases in erectile activity in healthy subjects compared to placebo in a randomized double-blind trial, with duration of erections with rigidity greater than 60% base reaching approximately 140 minutes at the 20 mg dose — demonstrating substantially greater effect magnitude than MT-2 at its studied doses.
FDA approval of bremelanotide (Vyleesi) in 2019 for HSDD in premenopausal women represents the clinical regulatory endpoint of the research trajectory that began with MT-2’s unexpected erectogenic adverse event observations in 1996.
Safety Context — Melanoma Case Reports
MT-2’s most significant safety concern — and the primary reason it has not advanced to clinical regulatory approval — is the documented occurrence of melanoma in individuals who self-administered MT-2 outside of controlled clinical settings. Multiple case reports have been published in peer-reviewed dermatology journals documenting melanoma arising in individuals with documented MT-2 self-administration history.
The biological mechanism for this risk is plausible and direct: MC1R activation by MT-2 stimulates melanocyte proliferation — the same cell type that gives rise to melanoma. MC1R variants (loss-of-function) are among the strongest known genetic risk factors for melanoma susceptibility. An MC1R agonist that simultaneously drives melanocyte proliferation in populations that may already carry elevated melanoma risk through MC1R variant alleles represents a pharmacologically meaningful carcinogenic concern.
The documented adverse events with unregulated MT-2 self-administration (obtained through non-pharmaceutical channels) include melanoma at injection sites, rapid darkening and morphological changes of pre-existing nevi, development of new atypical pigmented lesions, rare cases of priapism (sustained involuntary erection) requiring medical intervention, systemic toxicity and rhabdomyolysis (documented in one published case report), and injection-related complications including infection risk from non-sterile technique.
These safety signals are the mechanistic and clinical reasons why MT-2 did not proceed through the full clinical development pathway that produced afamelanotide (MT-1) and why regulatory approval has not been pursued or obtained. Any researcher or individual who has used MT-2 should undergo thorough dermatological examination for skin lesion changes.
MT-2 vs MT-1: The Critical Distinction
The two Melanotan compounds are frequently conflated in popular discourse, and accurate differentiation is essential.
MT-1 (afamelanotide/Scenesse) is FDA-approved, has completed Phase 3 trials published in NEJM, has 8+ years of long-term safety data, no documented melanoma signals in clinical trial populations, and relative MC1R selectivity that avoids significant CNS effects.
MT-2 has no regulatory approval in any jurisdiction, has only early Phase 1-2 human data, has documented melanoma case reports in self-administering populations, activates MC3R, MC4R, and MC5R in addition to MC1R producing CNS effects including spontaneous erections and appetite suppression, and remains an unregulated research compound.
The two compounds share the alpha-MSH pharmacological ancestry and MC1R-mediated melanogenesis mechanism, but are pharmacologically, structurally, and regulatory-status-wise distinct compounds that should not be treated as interchangeable.
MT-2’s Research Legacy: The Bremelanotide Pathway
While MT-2 itself has not achieved clinical approval, its research legacy is substantial. The two controlled human trials by Wessells and colleagues at the University of Arizona constituted the essential proof-of-concept evidence that MC4R agonism produces spontaneous erections and increases sexual desire in humans through central neural mechanisms. This evidence directly enabled the clinical development of PT-141 (bremelanotide), which progressed through full Phase 2 and Phase 3 clinical development and received FDA approval in 2019 as the first centrally-acting treatment for female hypoactive sexual desire disorder.
In research pharmacology, MT-2 remains a useful non-selective melanocortin receptor tool for studies requiring simultaneous engagement of multiple melanocortin receptor subtypes, and for receptor binding and pharmacology studies where comparing MC1R-selective agonism (MT-1) with non-selective agonism (MT-2) is the experimental objective.
Current Research Status
MT-2 has no current active clinical development programs and no regulatory approval pathway in any jurisdiction. It is classified as a prohibited substance by WADA and a prohibited/scheduled substance in multiple countries. The clinical research directions it catalyzed — sexual dysfunction treatment through melanocortin receptor agonism — have been carried forward by bremelanotide (PT-141) and other more selective melanocortin analogs rather than by MT-2 itself.
Reconstitution Note
MT-2 is a synthetic cyclic heptapeptide. Bacteriostatic water is the standard reconstitution solvent. MT-2 dissolves readily in aqueous solution. Protect from light. Always confirm the recommended solvent against the specific lot datasheet before reconstitution.
In-Use Period and Storage
Before Reconstitution — Lyophilized Powder
Rogue Compounds stores all products refrigerated prior to shipping to maintain compound integrity from production through to delivery. Upon receipt researchers should store vials at 2 to 8 degrees Celsius immediately. Keep vials sealed, dry, and away from direct light until ready for use. Do not freeze. Repeated freeze-thaw cycling has been documented in peer-reviewed pharmaceutical formulation literature to accelerate structural degradation even in dry powder form, potentially compromising molecular integrity and experimental reproducibility.
Why We Refrigerate Instead of Freeze
Freezing and thawing introduces mechanical and osmotic stress at the molecular level. Published pharmaceutical research identifies freeze-thaw cycling as a significant risk factor for loss of structural integrity in peptides and protein-based compounds. To protect compound quality at every stage of handling and fulfillment, Rogue Compounds maintains refrigerated rather than frozen cold chain storage throughout the entire process.
After Reconstitution — Liquid Solution
Store reconstituted solutions refrigerated at 2 to 8 degrees Celsius immediately after preparation. Protect from light at all stages of storage and handling. Avoid repeated freeze-thaw cycles. Use within the timeframe recommended for the individual compound. Label each aliquot with the compound name, concentration, date of reconstitution, and diluent used. Discard any solution that shows visible particulate matter, discoloration, or signs of degradation.
Note: Storage and in-use recommendations on this page are provided as general laboratory guidance based on standard peptide handling practices documented in peer-reviewed pharmaceutical literature. Researchers should always refer to the individual compound’s published research literature and datasheet for any specific requirements. All products sold by Rogue Compounds are intended strictly for in-vitro laboratory research use only.
Available from Rogue Compounds
View the MT-2 product page: https://roguecompounds.com/product/mt-2/