RESEARCH INDEX / MELANOCORTIN MC1R-MC4R
Melanotan 2 is a synthetic melanocortin peptide studied for pigmentation, appetite, and behavior.
One molecule. Four receptors. A literature read brain-first. Every figure on this site is attributed to a study.
The short version
Melanotan 2 is a lab-made copy of a natural body signal called alpha-MSH (a hormone that tells skin cells to make pigment). Injected, it switches on a set of receptors — docking points on cells — called melanocortin receptors. The headline result: skin darkens without sun. But the same receptors sit in the brain, and that is where the more interesting story lives. In animals, the peptide cuts appetite, triggers erections in males, and shifts mood and social behavior. In a small human pilot, it darkened skin and produced spontaneous erections [1].
None of this is approved medicine. Melanotan 2 has no green light from any drug regulator, anywhere [4]. It is sold as an unregulated research chemical, and case reports tie it to darkened moles, kidney injury, and prolonged painful erections. What people report — the upsides and the downsides — is on the effects page. This site digests the studies. It is not a clinic and sells nothing.
The brain is the headline, not the tan
Most coverage of Melanotan 2 stops at the skin. The published record runs deeper. The same melanocortin receptors that drive pigment also sit in the hypothalamus and the mesolimbic reward system — the brain's appetite and motivation circuits.
In male mice, Melanotan II microinjected directly into the nucleus accumbens (a reward hub deep in the brain) cut food intake and food-seeking — without making the animals sick and without changing their metabolic rate [5]. In rats, intravenous Melanotan II switched on oxytocin neurons in the hypothalamus, the cells behind the "bonding" hormone [8]. A 2024 study sharpened the link: melanocortin signaling lit up the nucleus accumbens in a social setting, and the effect depended on oxytocin [9].
This is the neuro-behavioral lens. Appetite, sexual motivation, mood, social behavior — all routed through MC4R in the brain. The melanotan 2 mechanism of action page maps the wiring.
What the human data actually shows
Human evidence is thin and old. Two small Phase I studies, decades apart in design but both tiny.
The pigmentation pilot: 3 healthy men, subcutaneous Melanotan II escalated from 0.01 to 0.025-0.03 mg/kg. Skin darkened in 2 of 3 after only 5 low doses, with spontaneous erections lasting 1-5 hours and mild nausea [1]. These are study-design facts, not a dosing guide — Melanotan 2 is not approved for human use.
The erection study: 10 men with psychogenic erectile dysfunction, a single 0.025 mg/kg subcutaneous dose. Clinically apparent erections in 8 of 10; mean duration of firm rigidity was 38.0 minutes versus 3.0 minutes on placebo [2]. No Phase II or Phase III trial has ever been completed for Melanotan 2 itself [4].
What to watch for
The caveats are real and case-reported. Because the peptide wakes up pigment cells everywhere, existing moles darken and new ones can appear — and a handful of melanoma cases have been reported in users [10]. A nephrology case report ties it to renal infarction (a blocked blood supply to the kidney), and notes prior reports of muscle breakdown and kidney failure [4].
The product itself is a problem. Online "melanotan" is unregulated: forensic analyses find mislabeled, variable, and impure vials. A buyer cannot know what is actually inside.
Full, cited detail sits on the Melanotan 2 effects page and the Melanotan 2 research record.