Melanocortin

Melanotan II

A ring-shaped peptide that activates melanocortin receptors, including the receptor that signals skin cells to make pigment.

The melanocortin pathway.

Melanotan II mimics part of alpha-MSH, a hormone involved in pigment production. It activates several melanocortin receptors, connecting its effects on skin color with effects on appetite and sexual response.

How it works.

Alpha-MSH analog: The peptide mimics activity of alpha-melanocyte-stimulating hormone at melanocortin receptors.
MC1 receptor: Activation of MC1 receptors on melanocytes stimulates the pathway that produces melanin.
Melanin production: Melanocytes make melanin and transfer pigment-containing structures to neighboring skin cells.

Useful terms

Melanocyte: A cell that produces melanin.
Cyclic peptide: A peptide with a ring within its molecular structure.
Alpha-MSH: Alpha-melanocyte-stimulating hormone.

Results.

Human pilot · three volunteers

Increased skin pigmentation.

A 1996 pilot found increased pigmentation in two of three participants after a short treatment period. A separate placebo-controlled study in ten men with erectile dysfunction found that Melanotan II also initiated erections.

Pigmentation study · Dorr et al., 1996 Erectile-response study · Wessells et al., 1998

Risks, concerns & drawbacks.

Reported side effects: Nausea, yawning, fatigue or sleepiness, reduced appetite, and spontaneous erections were reported in the early human studies.
Pigment changes: Case reports describe new moles and darkening of existing moles. New or changing spots deserve an examination.
Prolonged erections: Published case reports describe painful, prolonged erections requiring emergency treatment. An erection lasting four hours needs urgent medical care.
Longer-term use: The early trials were small and brief. They do not describe the effects of years of repeated use.

Human side-effect observations · 1996 Appetite observations · 1998 Priapism case report · Mallory et al., 2021 Mole changes · Schulze et al., 2014