Melanotan II
Melanotan II — the tanning peptide: evidence, the discovery story & serious risks

Class: peptide
Synonyms: Melanotan II
MT-II
MT-2
"the tanning peptide"
a synthetic α-MSH analog. INCI: none
Function tags: skin tanning
sexual arousal (gray-market / research)
Overall evidence grade: C
WADA prohibited: no
Last updated: 2026-07-13

In brief: Melanotan II is a non-selective melanocortin agonist — the original "tanning peptide." It genuinely does induce a tan (and arousal), but it is not approved anywhere, sits in FDA Category 2 for safety risks, and is linked in case reports to serious harms — priapism, mole/pigment changes, rhabdomyolysis, kidney injury and more. "Safe sunless tanning" is a dangerous misframing. Its erectile side effect gave rise to the FDA-approved drug PT-141 (#46), and its relative Melanotan I (afamelanotide) is separately approved for a rare disease — but MT-II itself is the unapproved, higher-risk one.

## Identity a synthetic **cyclic heptapeptide** (7 amino acids), sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂ — a **non-selective melanocortin agonist** (activates MC1R, MC3R, MC4R and MC5R), up to ~1000× more potent than natural α-MSH at stimulating melanin, and able to cross the blood-brain barrier (hence the central effects). ## Development & history - Groundwork: 1960s research showed α-MSH triggered **sexual arousal in rats**; interest carried into the 1980s.
- At the **University of Arizona (1980s–early 1990s)**, **Mac E. Hadley** and **Victor J. Hruby** set out to build α-MSH analogs as **sunless-tanning / skin-cancer-chemoprevention agents** — the idea being a protective tan without UV. They synthesised **Melanotan-I** and **Melanotan II**.
- **The pivotal accident:** while self-experimenting with Melanotan II, one of the scientists **injected ~twice the intended dose and got an ~eight-hour erection, plus nausea and vomiting** — revealing that MT-II acts centrally (MC4R) as well as on skin (MC1R). A 1996 pilot (Dorr et al., Life Sciences, 3 volunteers) then documented dose-dependent tanning alongside nausea, flushing and spontaneous erections.
- Australian-government-funded human trials followed (Hadley, late 1990s), but the **side-effect burden showed it was impractical** as a drug, and **it was never approved.** The erection finding was spun off into **PT-141 / bremelanotide (#46)** — which *was* eventually FDA-approved. **MT-II itself went gray-market**, sold online and in tanning salons and gyms from the mid-2000s. ## Mechanism (as proposed) a **non-selective melanocortin agonist** — **MC1R** on skin melanocytes → melanin synthesis (tanning); **MC4R** in the hypothalamus → sexual arousal/erection and appetite suppression; plus MC3R/MC5R. Because it crosses the blood-brain barrier, the central (MC4R) effects accompany the skin (MC1R) effect — which is exactly why a "tanning" compound also causes erections, nausea and other systemic effects.

Evidence grades by outcome:
outcome: Skin tanning (the marketed use)
grade: C
base: Small human studies (Dorr 1996; Phase 1 tanning)
effect: Genuine, dose-dependent tanning
caveat: The effect is real, but no completed safety/efficacy trial; not approved; efficacy is not the problem — safety is
outcome: Erectile / arousal effect
grade: C
base: Small trials (Wessells 1998)
effect: Erection induction
caveat: This effect became PT-141's domain; MT-II itself unapproved
outcome: "Safe sunless tanning" claim
grade: F
base: —
effect: Misframing
caveat: The risk profile below makes "safe" inaccurate
outcome: Safety / serious adverse events
base: Case-report literature + trial AEs
effect: Serious concerns
caveat: Documented in case reports: priapism (sometimes needing surgery), changing/darkening moles (complicating melanoma detection), rhabdomyolysis, renal infarction, posterior reversible encephalopathy syndrome (PRES); plus routine nausea/flushing. Whether MT-II causes melanoma is unproven and confounded by users' extra UV-seeking — but the pigment/mole changes are a real monitoring problem

Legal status:
region: US
status: Not FDA-approved (503A Cat. 2)
note: FDA classifies MT-II in Category 2 of the 503A bulks list (a substance that raises significant safety risks for compounding).
region: EU
status: illegal to sell for human use
note: illegal to sell for human use; nonetheless widely available through internet vendors and gym/salon networks, marketed as a tan.

Cosmetic claims:

Note: Reference entry — not sold here. Melanotan II is not approved anywhere, sits in FDA Category 2 (significant safety risks), and is illegal to sell for human use in most countries. Unusually for this register, the marketed effect (tanning) is real — but the compound is genuinely unsafe, which is the whole point of the page. No dosing published here.

Sources:
Dorr RT, et al. (Phase 1 pilot of melanotan-II — tanning + adverse effects.) Life Sci. 1996.
Wessells H, et al. (Melanotan-II erectile-response trials.) J Urol, 1998.
Hadley ME. Discovery that a melanocortin regulates sexual functions in male and female humans. Peptides. 2005.
Case-report literature on priapism, melanoma/nevus changes, rhabdomyolysis, renal infarction, PRES; melanoma-risk reviews (2013; 2021).