Melanotan II (MT-II) is a synthetic cyclic heptapeptide developed at the University of Arizona in the 1980s-1990s as a potential photoprotective agent. It is an analog of alpha-melanocyte stimulating hormone (alpha-MSH) designed to stimulate melanin production and produce a protective tan without UV exposure. Cyclization of the peptide backbone (compared to the linear Melanotan I/afamelanotide) was introduced to prevent enzymatic degradation and allow both N- and C-terminal truncation.
MT-II is classified as a non-selective melanocortin receptor agonist, meaning it activates four of the five known melanocortin receptors: MC1R (melanocytes/skin), MC3R (brain/gut), MC4R (hypothalamus/CNS), and MC5R (exocrine glands). This broad receptor coverage produces effects well beyond tanning: MC4R activation causes sexual arousal and appetite suppression, MC3R activation influences energy homeostasis, and the combination produces the multi-system effects that define MT-II's pharmacological profile.
The pro-erectile activity of MT-II was discovered as an unexpected side effect during a Phase I tanning trial when dermatologist Norman Levine noted that male participants presented with spontaneous erections. This observation led directly to the development of PT-141 (bremelanotide), a metabolite of MT-II that was refined into an MC4R-focused therapeutic and ultimately achieved FDA approval in 2019 as Vyleesi for hypoactive sexual desire disorder in premenopausal women.
Critical context: While MT-II's derivative (PT-141) achieved FDA approval for a specific indication, MT-II itself has never been approved anywhere in the world. It carries significant safety concerns including published case reports of mole changes, new nevi development, and melanoma diagnoses in users. The compound's non-selective receptor activation means it cannot be used for tanning without simultaneously affecting sexual function, appetite, cardiovascular parameters, and potentially melanocyte biology in unpredictable ways.
| Weeks | Dosage | Syringe units (U-100) |
|---|---|---|
| Week 1 | 0.25 mg | 7.5 units0.07 mL |
| Week 2 | 0.5 mg | 15 units0.15 mL |
| Week 3 | 0.75 mg | 22.5 units0.22 mL |
| Weeks 4–8 | 1 mg | 30 units0.3 mL |
FrequencyOnce daily, subcutaneous.
For review — the cited studies dosed once per visit, not daily. Wessells et al. gave a single 0.025 mg/kg subcutaneous dose at each study visit for a different indication; the daily ladder in the chart follows a circulated research protocol. The concentration strip above the chart is calculated from the vial and water volume and is correct.
Unverified — the cited human studies used single doses per visit, not a daily course.
Melanotan II was studied in humans in the 1990s and 2000s for erectile dysfunction, at a single body-weight dose per study visit, and was then abandoned without approval anywhere — so a daily fixed-milligram course run for eight weeks is not what the cited work tested, and the chart is flagged for review. The side effects that limited those studies are the reason the ladder starts low: nausea, flushing and spontaneous erection were dose-related, and darkening of existing moles is the effect that has drawn dermatological concern about unsupervised use. Afamelanotide is a related approved compound with a different molecule and an implant delivery system; its label does not transfer to these rows. Athena lists one strength, and a 10 mg vial made up with 3 mL is about 3.33 mg/mL, so the ladder runs 7.5, 15, 22.5 and 30 units — all within one 50-unit syringe.
What this evidence establishes. Melanotan II was studied in humans in the 1990s and 2000s and then abandoned; it has never been approved anywhere. The dose below comes from single-dose studies for a different indication than the one it is now used for, and side effects — nausea, flushing, spontaneous erection, and darkening of existing moles — were dose-limiting in those studies. Afamelanotide, a related and approved compound, has a different molecule, a different delivery system and its own label; its dosing does not transfer.
Sources: Wessells et al. — melanotan II erectile dysfunction studies
For educational and laboratory research purposes only. It does not provide medical advice, dosing recommendations, or instructions for human or veterinary use. Syringe units assume a U-100 syringe, on which 1 mL is 100 units and a 50-unit syringe holds 0.5 mL.
MT-II's effects are mediated through simultaneous activation of multiple melanocortin receptor subtypes. Each receptor produces distinct physiological effects:
Activates melanocytes to produce eumelanin (brown-black pigment), shifting production away from pheomelanin (red-yellow). Creates actual melanin deposition, not surface staining.
Activates hypothalamic MC4R to produce centrally mediated sexual arousal and erectile function. Acts through CNS pathways distinct from PDE5 inhibitors (Viagra). 10-100x superpotent vs endogenous alpha-MSH.
Hypothalamic melanocortin receptor activation reduces food intake and increases energy expenditure. MC4R is one of the most important regulators of energy homeostasis.
Facial flushing, blood pressure changes, and heart rate alterations reported. Melanocortin receptors are expressed in cardiovascular tissue.
Published case reports document darkening of existing moles, development of new nevi, and difficulty distinguishing benign changes from melanoma in MT-II users.
Nausea (most common complaint), yawning, stretching, and facial flushing particularly during initial loading. Mediated by central melanocortin receptor activation.
Key pharmacological distinction: MT-II vs PT-141 (Bremelanotide): PT-141 is a deaminated metabolite of MT-II that was engineered to focus on MC4R pathways for sexual function without significant MC1R tanning effects. PT-141 achieved FDA approval (Vyleesi, 2019) for hypoactive sexual desire disorder in premenopausal women. MT-II, with its broad receptor activation, has never been approved for any indication.
MT-II has been administered to humans in early clinical trials, but its safety profile raises significant concerns. The following data combines published clinical trial observations and published case reports:
| Condition / Factor | Risk Level | Rationale |
|---|---|---|
| History of melanoma or atypical moles | HIGH | MT-II stimulates melanocyte activity. Multiple published case reports document mole changes, new nevi, and melanoma diagnoses in users. Causation not established but association warrants extreme caution. |
| Fair skin with many moles (dysplastic nevus syndrome) | HIGH | Individuals with numerous atypical moles are already at elevated melanoma risk. Stimulating melanocyte proliferation and activity compounds this risk. |
| Cardiovascular disease | HIGH | Blood pressure changes, facial flushing, and heart rate alterations reported. Melanocortin receptors expressed in cardiovascular tissue. Pressor effects documented in clinical studies. |
| Pregnancy / breastfeeding | HIGH | No reproductive toxicology data. Excluded from all clinical trials. Hormonal and melanocyte-activating effects pose unknown risks to fetal development. |
| Nausea / GI distress | MODERATE (expected) | Most commonly reported side effect, especially during initial use. Central melanocortin activation triggers nausea pathways. Often severe enough to limit use. |
| Priapism risk | MODERATE | Prolonged erections reported in clinical studies. MC4R-mediated erectile activity can be unpredictable in timing and duration. |
| Uneven pigmentation | MODERATE | Hyperpigmentation of lips, genitals, scars, and skin folds reported. Pigmentation changes may be uneven and cosmetically undesirable. |
| Hormonal effects in women | MODERATE (understudied) | MC4R activation affects hypothalamic function. Effects on menstrual cycle, reproductive hormones, and fertility in women are poorly characterized. |
| Quality control (peptide supplier sourcing) | HIGH | Source quality varies significantly by supplier. Purity, sterility, and accurate dosing should be verified through third-party testing and Certificates of Analysis. |
| Human safety data | LIMITED | Early Phase I/II data exists for tanning and erectile function. Safety database is small. Long-term melanocyte stimulation effects are unknown. Published case reports raise serious dermatological concerns. |
FDA: Melanotan II is NOT FDA-approved for any indication. It has never completed the clinical development program required for regulatory approval. Its derivative, PT-141 (bremelanotide/Vyleesi), is FDA-approved for a specific indication (HSDD in premenopausal women), but this does not extend approval to MT-II.
EMA: Not approved. Melanotan I (afamelanotide/Scenesse) is approved in the EU for erythropoietic protoporphyria, but this is a different, more selective compound.
Global Regulatory Warnings: Multiple countries including the UK (MHRA), Australia (TGA), and Denmark have issued public warnings about Melanotan II, citing unregulated sale, unknown purity, and potential health risks including melanoma concerns.
Key distinction: MT-II is not simply "an unapproved version of an approved drug." Its non-selective receptor activation profile is fundamentally different from the targeted MC4R agonism of PT-141 or the MC1R selectivity of afamelanotide. The broad receptor activation that produces MT-II's multi-system effects is precisely what makes it unsuitable for regulatory approval as a single-indication therapeutic.
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This profile is for educational and research purposes only. It is not medical advice, and nothing on it is a protocol, a recommendation, or an instruction for use in a person or an animal.
Athena Peptides Education does not prescribe, sell, or recommend any compound. Compounds discussed here are for laboratory research only and are not for human consumption. Always consult a qualified physician before making any decision about your health.