Melanotan II has circulated in the cosmetic and bodybuilding underground since the late 1990s as an injectable tanning agent. Its mechanism — broad agonism across melanocortin receptors MC1R through MC5R — produces the pigmentation effect but also drives the adverse-effect profile, including the sexual-arousal effects that later motivated development of the MC4R-selective derivative bremelanotide (PT-141).
Unlike many peptides in the research-chemical market, melanotan II has accumulated a peer-reviewed case-report literature spanning more than fifteen years. The signal is narrow — case reports are not population incidence data — but consistent: dermatology, urology, and nephrology journals have separately documented serious adverse outcomes in otherwise-healthy users. This piece reviews what that literature actually shows, and why PeptaHub's editorial stance is that melanotan II should not be recommended even for cosmetic use.
The melanoma signal
The earliest widely cited report is Paurobally et al., British Journal of Dermatology, 2011 — a 42-year-old white woman who developed melanoma (Breslow thickness 0.30 mm, Clark level II) in a pre-existing melanocytic nevus following subcutaneous melanotan II injections. Hjuler and Lorentzen, Dermatology, 2014 documented a 20-year-old woman who developed a biopsy-confirmed melanoma after three to four weeks of self-injected melanotan II combined with tanning-bed use.
These are case reports, not causal epidemiology. The mechanism is biologically plausible — non-selective melanocortin-receptor agonism stimulates melanocyte proliferation, and independent case series have documented eruptive nevi and atypical nevi in melanotan users. What the literature does not establish is baseline melanoma incidence among users. What it does establish is that dermatology journals consider the signal strong enough to publish, and that the UK regulator (MHRA) and Australian regulator (TGA) have both issued public warnings against cosmetic use.
Beyond melanoma: systemic adverse events
The case-report literature extends beyond dermatology. Dreyer, Amer, and Fraser (2019) documented melanotan-induced priapism — a urologic emergency in which spontaneous, prolonged erection causes ischemic injury to penile tissue if untreated. Peters et al., 2020 reported a case of renal infarction in a melanotan II user and reviewed prior renal-adverse-event literature. DermNet NZ's clinical reference summarizes additional documented effects including rhabdomyolysis (muscle-cell breakdown), encephalopathy syndrome, and melanonychia (nail pigmentation).
Several of these events are serious in their own right. Priapism over four hours is a tissue-preservation emergency. Rhabdomyolysis can precipitate acute kidney injury. None of these are common in the reported population, but none of them have plausible alternative explanations when they occur in young, healthy users whose only exposure variable is injectable melanotan II.
Regulatory posture
Melanotan II has never been FDA-approved for any indication. It is sold in the US and Europe as a research chemical and is commonly mislabeled as "cosmetic." UK (MHRA), Australia (TGA), and EU member-state regulators have issued public warnings. Sourcing via unregulated vendors adds a separate risk layer: contamination from non-sterile preparation, dose inaccuracy, and counterfeit products have all been documented.
The practical read is this. PT-141, developed specifically for sexual dysfunction, has FDA approval (as bremelanotide, Vyleesi) and a regulated safety dossier. Melanotan II does not, and the population that could have generated a rigorous safety dataset — cosmetic users over two decades — was instead captured in a scattered case-report literature whose signal is narrow but uniformly unfavorable.
PeptaHub's skin peptide pillar covers melanotan II's mechanism and literature in more depth; our peptide-safety guide covers the sourcing-risk framework that applies to any research-chemical purchase. For cosmetic tanning specifically, the editorial position is that the case-report literature is sufficient to recommend against use.