Research digest / Melanocortin peptide
Melanotan 2 is one peptide in a family of three — and the family is the key to reading it.
The pigmentation analog became the photoprotection drug; the sexual-function spin-off became an approved medicine; the parent compound stayed unapproved and went underground. A cited digest of what the studies measured.
The short version
Melanotan 2 (often written MT-2 or MT-II) is a lab-made copy of a natural body signal that tells skin cells to make more pigment. It was built in the 1980s to darken skin without sun, in the hope of cutting skin-cancer risk. In early human tests it did tan people — but it also triggered erections and killed appetite, because the same signal acts on the brain as well as the skin.
That one peptide spawned two relatives. A close cousin, afamelanotide, became an approved drug for a rare light-sensitivity disease. A spin-off, bremelanotide, became an approved drug for low sexual desire in some women. Melanotan 2 itself was never approved anywhere and is now sold illegally online as tanning injections.
People report a fast tan, less hunger, and a higher sex drive — and also nausea, darkening moles, and worse. What people actually report, including the downsides, is on the effects page. This site reads the published record on all three; nothing here is a dose, a product, or medical advice.
What the Melanotan 2 literature actually shows
Melanotan 2 is a cyclic (ring-shaped) synthetic analog of alpha-melanocyte-stimulating hormone, or alpha-MSH (the body's own pigment-signaling hormone). It activates all five melanocortin receptors (MC1R through MC5R), the cell-surface switches that hormone normally flips [1]. Designed by Victor Hruby and Mac Hadley at the University of Arizona in the late 1980s, it was engineered to be far more potent than the natural hormone and to resist the enzymes that break peptides down [1].
In the first human study — a single-blind, placebo-controlled pilot in three healthy men — five low subcutaneous doses (0.01 to 0.03 mg/kg, a study-design fact, not a dosing instruction) measurably darkened the face, upper body, and buttocks in two of three subjects, without any UV exposure [2]. The same men experienced spontaneous erections lasting one to five hours and mild nausea [2]. That accidental finding redirected the research: a later double-blind crossover study in ten men with psychogenic erectile dysfunction produced erections in eight of ten, with a mean of 38 minutes of rigidity versus 3 minutes on placebo [3].
This is the central fact about Melanotan 2 — one molecule, several effects, because melanocortin receptors sit in the skin, the brain's appetite centers, and the circuits that govern sexual function all at once.
Three peptides, one receptor family
Reading Melanotan 2 in isolation misses the point. Its story is a family story, and the family is the most useful frame [4].
Afamelanotide (Melanotan I) is the linear, MC1R-leaning analog. It went the distance: two multicenter Phase 3 trials in erythropoietic protoporphyria — a rare inherited disorder that makes sunlight painful — showed longer pain-free sun exposure and fewer phototoxic reactions, and it won regulatory approval for that condition [5]. It is the only melanocortin tanning analog with an approval anywhere.
Bremelanotide (PT-141) is the sexual-function descendant, optimized from the Melanotan 2 scaffold toward MC4R activity (the appetite-and-sex receptor) with less pigment activity [6]. It is approved for low sexual desire in some premenopausal women; a functional-MRI study found MC4R agonism increased self-reported desire and changed brain activation during erotic cues versus placebo [7].
Melanotan 2 is the parent — the broad, non-selective agonist that does a bit of everything and was never approved for anything. The full side-by-side is on the melanotan 2 vs pt-141 page. The crucial caveat: the approvals of the cousins do not transfer to the parent.
What people seek it for — and what to watch
Outside the lab, Melanotan 2 is used for one headline reason: a fast, deep tan with little sun. Users also frequently report appetite suppression and a sharp rise in libido. Those reports are consistent and they are why the underground market exists [8].
They are also only half the picture. The same melanocortin activity that darkens skin darkens moles — and case reports document eruptive new moles, atypical (dysplastic) moles, and melanoma in users [9]. Serious harms include renal infarction, rhabdomyolysis (severe muscle breakdown), priapism (a prolonged, dangerous erection), and a reversible brain-swelling syndrome called PRES, each documented in the literature [10]. Products bought online are unregulated and frequently mislabeled or impure [11].
The honest, plain-English account of the benefits people report and the risks the studies document — kept clearly apart — is on the effects page. The mechanism is on the Melanotan 2 research page; the study-context numbers are on the dosage page; the sources are in the Melanotan 2 references.