One tanning peptide became a medicine. The other became a dermatologist’s warning

Both Melanotan peptides copy alpha-MSH, the hormone that tells skin to make melanin. Their stories then split.

Melanotan I, now called afamelanotide, went through proper trials for erythropoietic protoporphyria, a rare disease that makes sunlight painful. In the US trial of 94 patients, those given the implant spent a median of 69.4 hours in direct sunlight without pain over six months, compared with 40.8 hours on placebo. In the European trial of 74 patients, painful reactions were less frequent (77 versus 146). It is approved for this disease as Scenesse.

Melanotan II was tested in a 1996 pilot study in three healthy men over two weeks. It darkened the skin of two of them. It also caused mild nausea at most dose levels, sleepiness and tiredness in one man, and spontaneous erections lasting one to five hours.

It never went on to approval, but it spread through gyms and tanning salons. Dermatologists reported a 20-year-old woman diagnosed with melanoma, a dangerous skin cancer, three months after a three- to four-week course of self-injected Melanotan II combined with sunbeds. Other doctors have reported a kidney infarction, where part of a kidney loses its blood supply. Case reports cannot prove cause, but they flag risks that no trial has measured.

A 2026 review of unregulated “biohacking” drugs lists Melanotan II among unapproved peptides that “lack established human safety profiles”, with risks including contamination and inaccurate dosing.

Its relative PT-141 took the opposite path and became an approved medicine. Melanotan research material is listed in the research shop for laboratory use only.