Melanotan I (Afamelanotide) — selective and steady
Melanotan I is a linear α-MSH analog that binds primarily to the MC1 receptor (the melanocortin receptor responsible for pigmentation). The selectivity means fewer off-target effects — no significant libido or appetite changes. Onset is slower and pigmentation builds more gradually, but the result is a more even, longer-lasting tan. Afamelanotide is approved in Europe and the US for erythropoietic protoporphyria.
Melanotan II — cyclic and broader-acting
Melanotan II is a cyclic peptide that binds multiple melanocortin receptors (MC1, MC3, MC4, MC5). The broader receptor profile produces faster tanning, but also off-target effects: appetite suppression, libido enhancement, and occasional flushing or nausea during dosing.
Side effect profile
MT-II's broader receptor binding is responsible for most reported side effects: nausea (especially at first dose), facial flushing, increased moles or freckle darkening, and spontaneous erections in male subjects. MT-I's selectivity largely eliminates these — it is the cleaner research compound, at the cost of slower onset.
Dosing and protocol
MT-I research protocols typically use 0.5–1 mg daily during a loading phase, then weekly maintenance. MT-II uses 250–500 mcg daily during loading, tapered to 2–3x weekly. Both are subcutaneous and benefit from a 10–15 minute UV exposure within 24 hours of injection to drive pigmentation.