This entry gets blunt treatment rather than neutral framing, because the published harm record justifies it. The case literature includes melanoma diagnosed in users and eruptive or atypical nevi following use. Cousen and colleagues documented eruptive nevi in a user who also used tanning beds. Ellis and colleagues reported melanoma with a Breslow depth of 1 mm in a 23-year-old. Hjuler and Lorentzen published a melanoma case associated with melanotan II in Dermatology in 2014, and a 2024 report described melanoma in situ diagnosed weeks after use of product from a compounding pharmacy. Systemic toxicity has also been reported, including rhabdomyolysis described by Nelson and colleagues in 2012. Case reports establish association rather than causation, and that distinction should be preserved. But the mechanism is not obscure: this is a non-selective melanocortin agonist that stimulates melanocytes, and melanocytes are the cell of origin for melanoma. Association plus plausible mechanism plus three regulators issuing warnings is about as clear as a signal gets short of a trial nobody will ever run.