Melanotan 2: Safety Review of the Unapproved Tanning Peptide

Melanotan II (also written Melanotan-2 or MT-II) is a synthetic melanocortin-receptor agonist sold online and in gyms as an injectable “tanning peptide” — nicknamed the “Barbie drug” because it darkens skin and was also marketed for appetite suppression and libido. It is the experimental parent compound of bremelanotide, an approved female-libido drug, but Melanotan II itself is not approved as a medicine in any country. The FDA, the UK’s MHRA, and Australia’s TGA have all issued public warnings against buying or injecting it. It is sometimes lumped in with “weight-loss peptides,” but that framing is misleading: Melanotan II is a tanning compound, not a weight-loss treatment, and there is no approved indication and no human efficacy evidence for using it to lose weight. What the published literature does document is harm — nausea and flushing, blood-pressure changes, priapism, even renal infarction, and most worryingly a string of dermatology case reports of darkening and changing moles, eruptive and dysplastic nevi, and melanoma in people who injected it. This is a safety review, not a how-to guide.

The honest summary

• Not approved anywhere. Melanotan II is not an approved medicine in the US, UK, EU, or Australia. It is sold as an unregulated, often grey-market injectable, and regulators including the FDA, the UK MHRA, and the Australian TGA have publicly warned against its use^[6][7].
• It is a tanning peptide, not a weight-loss drug. Melanotan II is a synthetic analogue of α-melanocyte-stimulating hormone (α-MSH) developed to darken skin. There is no FDA-approved weight-loss indication and no human trial showing it is a safe or effective treatment for losing weight.
• It carries a real melanoma / mole safety signal. Multiple peer-reviewed case reports and reviews describe changing existing moles, new eruptive and dysplastic nevi, and even melanoma in situ in people who used it^{[1][2][3][4][5]} — the opposite of what you want from any product applied to your skin or pigment system.
• It causes systemic side effects. Documented effects include nausea, facial flushing, blood-pressure changes, spontaneous painful erections (priapism), and at least one reported case of renal (kidney) infarction^[8][9].
• The product itself is unverified. Vials are typically sold “for research use only” with no agency checking identity, purity, sterility, or dose — so injection-site infections and contamination are added risks on top of the drug’s own effects^[6].

What Melanotan II actually is

Melanotan II is a small synthetic peptide designed to mimic α-melanocyte-stimulating hormone (α-MSH), the body’s natural signal that tells pigment cells (melanocytes) to make more melanin. By activating melanocortin receptors — chiefly the MC1 receptor in skin and, less specifically, others such as MC4 in the brain — it drives skin darkening even without much sun exposure, which is why it was marketed as a “tan in a vial.” Because melanocortin receptors are also involved in appetite and sexual function, users reported reduced appetite and spontaneous erections, and the closely related compound bremelanotide (a different molecule) was later developed and approved specifically for low sexual desire in women. Melanotan II itself, however, never completed the clinical development needed for approval as a medicine, and it remains an unlicensed research compound sold direct to consumers as an injectable or, more recently, a nasal spray^[6][10].

It is not a weight-loss treatment

Melanotan II sometimes appears on lists of “weight-loss peptides” because melanocortin signaling (especially via the MC4 receptor) influences appetite. But there is a large gap between “touches an appetite pathway” and “is a safe, effective weight-loss medicine.” Melanotan II was developed and is used for tanning; it has no FDA-approved weight-loss indication and no human randomized trial demonstrating meaningful, safe weight loss. Any vendor presenting it as a slimming aid is making a claim the evidence does not support — and is asking people to inject an unapproved drug with a documented melanoma signal in pursuit of a benefit that has never been established in people. If weight loss is the goal, the evidence-based options are entirely different (see below).

The melanoma and mole safety signal

The most serious concern is dermatologic, and it is documented across more than a decade of peer-reviewed case reports. Because Melanotan II powerfully stimulates pigment cells, clinicians have repeatedly observed that users’ existing moles darken and change and that new pigmented lesions erupt after injection. A 2009 report in BMJ first publicly linked a change in moles to use of the unlicensed “sun tan jab”^[1]. A dermatology report the same year described α-MSH-induced eruptive nevi — a sudden crop of new moles^[3] — and later case reports documented eruptive dysplastic (atypical) nevi following melanotan use^[4][5]. Most alarming, a 2012 report described melanoma in situ — an early skin cancer — associated with melanotan use^[2], and a 2025 report raised the question of whether Melanotan II nasal spray could be a risk factor for oral mucosal malignant melanoma^[10].

Two reviews pull these threads together. A 2017 review in the International Journal of Dermatology on the “risks of unregulated use of α-melanocyte-stimulating hormone analogues” catalogues the dermatologic and systemic harms and the regulatory concerns^[6], and a 2017 commentary in the Australasian Journal of Dermatology argued that unregulated Melanotan II use is a genuine public-health issue warranting clinician attention^[7]. The mechanism makes biological sense: a drug that drives melanocyte activity is exactly the kind of agent you would not want to give to pigment cells that can turn cancerous. Whether Melanotan II causes melanoma or simply unmasks and accelerates changes in already-abnormal moles is not fully settled — but for a YMYL health decision, “an unapproved drug repeatedly associated with changing moles and melanoma in case reports” is reason enough to stay away.

Systemic side effects: more than skin

Melanotan II’s effects are not confined to skin. Commonly reported short-term effects include nausea, facial flushing, and yawning or stretching in the hour after injection, along with blood-pressure changes. Because melanocortin receptors influence sexual function, one of the more striking documented harms is priapism — a prolonged, painful erection that is a urological emergency — reported in association with Melanotan injection^[8]. More serious vascular events have also been described: a 2020 case report linked Melanotan II to renal (kidney) infarction^[9]. These reports involve an unregulated product at unknown doses, which makes the true rate of harm impossible to quantify — but it underscores that injecting this peptide is not a benign cosmetic shortcut.

Regulatory reality: warned against, not approved

Melanotan II has never been approved as a medicine in any major jurisdiction. In the United States it is not an FDA-approved drug and is not a legal dietary-supplement ingredient; the FDA has acted against tanning products containing it. In the United Kingdom, the medicines regulator (the MHRA) has repeatedly warned the public not to buy or use Melanotan because it is an unlicensed medicine of unknown quality. In Australia, the TGA treats melanotan peptides as unapproved and prohibited and has warned against their use, which is part of why Australian dermatologists flagged it as a public-health concern^[7]. The European picture is the same — it is not authorised, and national agencies have issued safety alerts. The consistent message from regulators across the US, UK, EU, and Australia is that Melanotan II is an unlicensed product that should not be injected^[6][7]. When you buy it, you are buying something no health authority has vetted.

If your goal is weight loss

Melanotan II should not be on the list. If you are looking for an actual weight-loss treatment, the evidence points to FDA-approved medications with large human trials behind them — not a tanning peptide. For context, semaglutide (Wegovy) produced roughly −15% mean body-weight change in a Phase-3 randomized trial and tirzepatide (Zepbound) up to about −21% in its Phase-3 program; both are approved, prescribed through licensed pharmacies, and manufactured under FDA-regulated conditions. That is the bar a weight-loss treatment should clear. For a fuller map of what is and is not legitimate in the peptide space, see our hub review of peptides for weight loss and the companion A-to-Z peptide evidence guide, plus the debunker on non-GLP-1 peptides marketed for fat loss.

Bottom line

Melanotan II is an unapproved tanning peptide, not a weight-loss medicine, and the published evidence on it is dominated by harm: changing moles, eruptive and dysplastic nevi, melanoma in situ, priapism, and even a reported kidney infarction, all from an unregulated injectable that no health authority has vetted. The FDA, the UK MHRA, and Australia’s TGA have all warned against it. There is no scenario in which injecting it for a tan — or, worse, for unproven appetite effects — is a sound trade. If you have used Melanotan and notice any new, changing, or atypical mole, see a dermatologist promptly. And if weight loss is the goal, look to FDA-approved medications with real human trials, not a grey-market tanning peptide.

This article is educational and is not medical advice. Every citation was verified against the live PubMed database before publication; the dermatologic, urologic, and vascular harms described are drawn from peer-reviewed case reports and reviews. Regulatory statements describe the publicly documented positions of the FDA, MHRA, and TGA. If you are considering any injectable peptide, or you notice a changing mole, consult a licensed clinician.