Melanotan II.
Melanotan II (MT-II) is a synthetic, cyclic heptapeptide analog of the natural hormone alpha-melanocyte-stimulating hormone (alpha-MSH).
Melanotan II (MT-II) is a synthetic, cyclic heptapeptide analog of the natural hormone alpha-melanocyte-stimulating hormone (alpha-MSH). Melanotan II is research / preclinical, and PepCue grades its published evidence D tier (38/100). This is a research reference, not medical or dosing advice.
What it is
Melanotan II (MT-II) is a synthetic, cyclic heptapeptide analog of the natural hormone alpha-melanocyte-stimulating hormone (alpha-MSH). It was developed at the University of Arizona in the late 1980s and 1990s as part of a program designing protease-resistant "superpotent" melanotropins; the related linear analog melanotan I became the approved drug afamelanotide (Scenesse). Unlike afamelanotide, Melanotan II itself was never approved as a medicine and today circulates almost exclusively as an unlicensed product sold online for cosmetic "tanning" and as a libido agent.
How it works
Melanotan II is a non-selective agonist of the melanocortin receptor family, binding MC1R, MC3R, MC4R and MC5R rather than selectively targeting MC1R. Activation of MC1R on cutaneous melanocytes stimulates the cAMP pathway and shifts melanin synthesis toward darker eumelanin, producing skin darkening that, unlike a UV tan, can occur with reduced sun exposure. Its central effects on sexual arousal and appetite are attributed mainly to MC4R (with possible MC3R contribution) in the hypothalamus and related circuits, while nausea, flushing and yawning also arise from this broad central melanocortin activation. The cyclic lactam structure makes it markedly more resistant to enzymatic degradation and more potent and longer-acting than native alpha-MSH.
Mechanism pathways
Engaging melanocortin receptors, relevant to pigmentation, sexual arousal, and inflammation.
The melanocortin system consists of five G-protein-coupled receptors, MC1R through MC5R, and their natural ligands derived from proopiomelanocortin, including alpha-melanocyte-stimulating hormone and adrenocorticotropic hormone. Each receptor subtype has a different distribution and a different job, which is why compounds acting on this family produce such varied effects depending on which receptors they touch. MC1R sits on epidermal melanocytes. Activating it raises cyclic AMP and shifts melanin synthesis toward eumelanin, the darker and more photoprotective pigment, independent of ultraviolet exposure. MC3R and MC4R are concentrated in the hypothalamus and limbic regions, where they participate in circuits governing appetite, energy balance, and sexual motivation. MC4R activation in particular is the accepted basis for centrally acting effects on arousal, which operate on motivation pathways rather than on vascular or genital tissue. MC5R is associated with exocrine gland function. Several melanocortin ligands also have anti-inflammatory activity, and this branch is pursued separately. Compounds in this group differ mainly by selectivity, and this is the distinction that determines both intended effect and side effect. A highly MC1R-selective analog is used to increase photoprotective pigmentation and is designed to avoid central receptors. Non-selective agonists bind across most of the family, which is why they produce pigmentation, appetite change, nausea, and arousal effects together rather than separately. A related tripeptide corresponding to the carboxy-terminal fragment of alpha-melanocyte-stimulating hormone retains anti-inflammatory activity but appears to work largely without classical melanocortin receptor engagement, entering cells through a peptide transporter instead. All of these analogs incorporate amino-acid substitutions that resist enzymatic breakdown, since the native hormones are short-lived. Clinical standing varies sharply within the group. Two members are approved medicines in at least some jurisdictions for narrowly defined indications, meaning their receptor mechanisms have been demonstrated in humans. Others in the group have never been approved anywhere and are sold as unregulated research chemicals. Non-selective melanocortin agonism in particular carries documented concerns including nausea, blood pressure effects, and changes to moles and pigmented lesions, and using pigmentation-inducing compounds without dermatological monitoring is widely cautioned against. Receptor pharmacology being well understood does not make an unapproved compound safe. The selectivity point is worth restating, because it is the single most useful thing to know about this family: the difference between a compound that touches one melanocortin receptor and one that touches all five is the difference between a narrow effect and a diffuse one.
The evidence
Human data on Melanotan II is limited to small, early-phase academic studies and a large body of case reports; no Phase 2/3 program was ever completed and it has never been tested in large controlled trials. The best-documented human work is on erectile function: a 1998 double-blind, placebo-controlled crossover study in men with psychogenic erectile dysfunction (Wessells et al., J Urol) and a 2000 study in men with organic erectile dysfunction (Urology) reported that subcutaneous Melanotan II initiated erections, accompanied by frequent nausea and yawning. Its tanning rationale rests on MC1R pharmacology and on the broader melanotan development program (Hadley et al., 1998), but rigorous controlled efficacy/safety data for cosmetic tanning in humans is essentially absent. Most contemporary human evidence comes from adverse-event case reports, including systemic toxicity with rhabdomyolysis (Clinical Toxicology, 2012) and dermatologic changes, so claims of benefit substantially outrun the controlled-trial evidence.
The evidence, in brief
A synthetic non-selective melanocortin agonist used unapproved for tanning and erectile effects, with no approved medical indication. Documented safety concerns include priapism, nausea/flushing, and changes to moles with melanoma case reports.
- Melanotan-induced priapism: a hard-earned tan (case report)BMJ Case Rep, 2019 (PMID 30796078)
Evidence maturity
An evidence-only reading: approval status, human vs preclinical data, mechanism and safety. Popularity never raises it. Research file #041
Mostly preclinical or mechanistic; little human data.
Some early human evidence exists but isn't definitive.
Claim receipts
Popular claims about Melanotan II, checked against the state of the evidence. The verdict describes evidence maturity, never an invented study result.
Unapproved; carries notable safety concerns and is not a sanctioned tanning method.
Safety profile
Commonly reported short-term effects in humans include nausea, vomiting, facial flushing, spontaneous yawning and stretching, appetite suppression, darkening of existing moles, and spontaneous erections or priapism in men. More serious documented harms from unregulated use appear in case reports: rhabdomyolysis and systemic toxicity, and a recurring concern about changes to melanocytic naevi (new and darkening moles, atypical naevi) with multiple published cases of melanoma reported in users, though causality has not been established and confounding by concurrent UV/tanning-bed exposure is a major limitation. Because the product is unlicensed and typically self-injected from non-pharmaceutical sources, contamination, mislabeling, dosing errors and sterility problems are additional, poorly quantified risks. This entry intentionally gives no doses or protocols; anyone considering use should consult a clinician, and dermatology bodies advise against use.
Compound notes
- Melanotan II is a synthetic cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone, developed at the University of Arizona as part of a program designing protease-resistant melanotropins.
- Unlike afamelanotide it is a non-selective melanocortin agonist, binding MC1R, MC3R, MC4R and MC5R. MC1R activation shifts melanin synthesis toward darker eumelanin, while central MC4R and MC3R activation accounts for effects on sexual arousal and appetite, and for nausea, flushing and yawning.
- Its cyclic lactam structure resists enzymatic degradation, making it more potent and longer-acting than native alpha-MSH.
- It was never approved and never completed Phase 2/3 development. Human data is limited to small early-phase studies, notably placebo-controlled work on erectile function, plus a large body of case reports.
Afamelanotide is the linear analog that completed trials and is FDA- and EMA-approved for erythropoietic protoporphyria, not for tanning. Melanotan II is the cyclic, non-selective sibling that circulates as an unlicensed product sold for cosmetic tanning.
- Not approved by any major regulator. The FDA, the UK MHRA and Australia's TGA have issued consumer warnings against it, and dermatology bodies advise against use.
- Commonly reported effects include nausea, vomiting, facial flushing, spontaneous yawning and stretching, appetite suppression, darkening of existing moles, and spontaneous erections or priapism in men.
- Case reports link unregulated use to rhabdomyolysis and systemic toxicity, and to melanoma, though causality is unproven and concurrent UV or tanning-bed exposure is a major confounder. Self-injected non-pharmaceutical product adds contamination, mislabeling and sterility risks.
Regulatory status
Melanotan II is not approved by the FDA or any major regulator for any indication and is not legally marketed as a medicine; products sold online are unlicensed. Regulators including the US FDA, the UK MHRA and Australia's TGA have issued consumer warnings against it. The distinct linear analog melanotan I (afamelanotide, Scenesse) is separately FDA- and EMA-approved, but only for erythropoietic protoporphyria, not for tanning.
Sold research-use-only; human evidence is limited or preclinical.
By the numbers
- 01Synthetic cyclic analog of alpha-MSH; non-selective agonist at MC1R, MC3R, MC4R and MC5R
- 02Developed alongside melanotan I (afamelanotide); only afamelanotide gained regulatory approval (for erythropoietic protoporphyria, not tanning)
- 03Never completed Phase 2/3 trials; human data limited to small early studies and case reports
- 04Unlicensed worldwide for human use; FDA, MHRA and TGA have warned consumers against it
- 05Documented effects include nausea, flushing, yawning, appetite loss, priapism, and mole darkening
- 06Case reports link unregulated use to rhabdomyolysis and to melanoma, though causality is unproven
Melanotan II: research formats
Choose the format you are researching to see route-specific notes.
Common research format; note the FDA has never approved Melanotan II.
Melanotan II is sold as a 10 mg lyophilized vial. It is not FDA-approved. Research use follows the standard subcutaneous format: reconstituted with BAC water. Melanotan II contains tryptophan and is light-sensitive: store in an amber vial and minimise light exposure during preparation.
Tryptophan-containing peptides (including Melanotan II) are photosensitive: wrap vials in foil or use amber glass. Significant Trp degradation can occur within hours of light exposure.
Sources
Every factual claim above resolves to a real, published source.
- Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction: double-blind, placebo controlled crossover studyThe Journal of Urology, 1998, PMID 9679884
- Effect of an alpha-melanocyte stimulating hormone analog on penile erection and sexual desire in men with organic erectile dysfunctionUrology, 2000, PMID 11018622
- Melanotan II injection resulting in systemic toxicity and rhabdomyolysisClinical Toxicology (Philadelphia), 2012, PMID 23121206
- Melanotan II (DermNet): unlicensed alpha-MSH analog, uses, regulatory warnings and adverse effectsDermNet NZ, dermatology reference
Cite this page
PepCue. “Melanotan II: the evidence.” PepCue, reviewed June 1, 2026. https://www.pepcue.app/p/melanotan-ii.
Log your doses, run the vial math, and keep a provider-ready record in PepCue.