Because Melanotan II is unapproved, its side effects are not documented in an approved label but in clinical case reports and warnings. Commonly reported short-term effects are nausea, facial flushing, and reduced appetite. In men, spontaneous erections are frequently reported, and priapism (a prolonged, painful erection) has been documented as a urological emergency.[1][2][3][4]
Reviewed for accuracy · Last reviewed July 8, 2026Because Melanotan II acts non-selectively across melanocortin receptors, effects extend beyond the skin. Blood pressure and cardiovascular or sympathetic changes have been reported, which is one reason its safety in an unregulated setting is hard to predict.
The concern that draws the most attention is the skin. Melanotan II stimulates melanocytes, and case reports describe pre-existing moles darkening and new atypical (dysplastic) moles erupting after use. Separate case reports describe melanoma in users, though these were often people who also used sunbeds, so a case report cannot establish that Melanotan II causes melanoma. The hedged reading is that this is a real, documented concern rather than a proven cause.
Anyone who has used Melanotan II should have a low threshold for a dermatology skin check and should watch for any mole that is new, changing, darkening, or irregular. A prolonged or painful erection needs emergency care, since untreated priapism can cause permanent damage.
This page is an independent educational reference and is not medical advice, and does not indicate any approval status for any use. Melanotan II is not approved by any regulator. Talk to a doctor before considering any compound.