Melanotan II (MT-2)
A non-selective melanocortin receptor agonist developed at the University of Arizona. Research applications span skin pigmentation, sexual dysfunction, and appetite regulation — with a complex regulatory history and significant safety considerations.
FDA Warning — Research Use Only
The FDA has issued warning letters to distributors of Melanotan II sold for human use. MT-II is not FDA-approved for any indication and is not intended for human administration. It is sold strictly for laboratory research. The related compound bremelanotide (Vyleesi) received FDA approval in 2019 for HSDD — it is a distinct compound and should not be confused with MT-II.
Mechanism of Action
Melanotan II is a cyclic analogue of alpha-melanocyte-stimulating hormone (α-MSH), a naturally occurring peptide derived from pro-opiomelanocortin (POMC). It binds with high affinity to melanocortin receptors (MCRs), which are G protein-coupled receptors distributed throughout the skin, brain, and peripheral tissues.
MT-II is administered subcutaneously. It is not orally bioavailable due to rapid proteolytic degradation in the GI tract.
Following absorption, MT-II crosses the blood-brain barrier and distributes to melanocortin receptor-expressing tissues throughout the body.
Binding to MC1R on melanocytes stimulates melanogenesis — the production of eumelanin (brown/black pigment). This produces the tanning effect without UV exposure.
Central melanocortin receptor activation suppresses appetite (MC4R hypothalamus) and activates pro-erectile pathways (MC3R/MC4R limbic system), producing the sexual and appetite effects.
MT-II has a short plasma half-life (~30–60 minutes). Effects on melanin synthesis persist longer due to downstream signaling, but CNS effects are more transient.
Melanocortin Receptor Binding Profile
MT-II is non-selective — it binds all five melanocortin receptor subtypes. This broad activity is the source of both its research utility and its side effect profile.
| Receptor | Primary Location | Effect of Activation | MT-II Affinity |
|---|---|---|---|
| MC1R | Melanocytes (skin, hair) | Melanin synthesis (tanning) | High |
| MC2R | Adrenal cortex | Cortisol release (ACTH receptor) | Low / non-selective |
| MC3R | Hypothalamus, limbic system | Energy homeostasis, sexual function | High |
| MC4R | Hypothalamus, brainstem | Appetite suppression, erectile function | High |
| MC5R | Exocrine glands, peripheral tissues | Sebaceous gland function | Moderate |
Research History
α-MSH identified as the endogenous melanocortin peptide responsible for skin pigmentation. University of Arizona researchers begin developing synthetic analogues.
Melanotan I (afamelanotide) synthesized. First-generation α-MSH analogue with longer half-life.
Melanotan II synthesized. More potent than MT-I with broader receptor activity including MC3R/MC4R. Accidental discovery of erectile effects in self-experimenting researcher (Dr. Hunter 'Mac' Hadley).
First published human trial of MT-II for erectile dysfunction. Wessells et al., Journal of Urology. Demonstrated efficacy but high nausea incidence.
PT-141 (bremelanotide) developed as a more selective analogue targeting sexual dysfunction without the broad tanning effect. Enters clinical trials.
FDA issues warning letters to distributors of MT-II sold as 'research chemicals.' Cites illegal marketing for human use without approval.
Bremelanotide (Vyleesi) receives FDA approval for HSDD in premenopausal women — the first FDA-approved melanocortin-based drug.
MT-II remains widely available through research chemical suppliers. Continues to be studied in preclinical models for melanoma prevention, obesity, and sexual dysfunction.
Melanotan II vs. Bremelanotide (PT-141)
These are related but distinct compounds. Bremelanotide was developed specifically to improve on MT-II's selectivity and safety profile for sexual dysfunction applications.
| Aspect | Melanotan II | Bremelanotide (PT-141) |
|---|---|---|
| Full name | Melanotan II | Bremelanotide (PT-141) |
| Structure | Cyclic heptapeptide analogue of α-MSH | Metabolite of Melanotan II; linear hexapeptide |
| FDA status | Not approved — FDA warning letters issued | FDA-approved (Vyleesi, 2019) |
| Approved indication | None | HSDD in premenopausal women |
| Primary research use | Tanning, sexual dysfunction, appetite suppression | Female sexual dysfunction (FDA-approved) |
| Melanocortin selectivity | Non-selective (MC1R, MC3R, MC4R, MC5R) | More selective for MC3R/MC4R |
| Tanning effect | Strong (MC1R agonism) | Minimal (reduced MC1R activity) |
| Route | Subcutaneous injection | Subcutaneous autoinjector (Vyleesi) |
| Half-life | ~30–60 min | ~2.7 hours |
| Nausea incidence | High (~80% in trials) | ~40% (dose-dependent) |
Side Effects & Safety Profile
The following adverse effects were documented in clinical trial data and case reports. The broad receptor non-selectivity of MT-II is the primary driver of its side effect burden compared to more selective analogues.
Frequency: Very common (>50%)
Most common adverse effect in clinical trials. Dose-dependent. Often occurs within 1–2 hours of administration.
Frequency: Very common (>50%)
Vasodilation effect. Typically transient (30–60 min).
Frequency: Common (males)
MC4R-mediated. Can be prolonged (priapism risk at high doses).
Frequency: Common
MC1R activation can darken existing melanocytic nevi. Requires dermatological monitoring. Potential melanoma risk signal.
Frequency: Common
Diffuse skin darkening beyond intended tanning effect. Can be uneven.
Frequency: Common
MC4R-mediated hypothalamic effect. Can cause unintended weight loss.
Frequency: Uncommon
Reported in some trial subjects. Mechanism unclear.
Frequency: Uncommon
Transient blood pressure elevation reported. Cardiovascular monitoring recommended.
Frequency: Unknown
MC1R activation promotes melanogenesis. Theoretical concern for melanoma promotion in susceptible individuals. No definitive causal data in humans.
Regulatory Status by Jurisdiction
FDA has issued warning letters to distributors. Not approved for any indication. Legal for laboratory research use only.
MHRA has issued multiple warnings about 'Barbie jab' products. Classified as a prescription-only medicine if sold for human use.
Listed as a Schedule 4 prescription-only medicine. Illegal to import or supply without a prescription.
No marketing authorization in any EU member state. Subject to national regulations.
Listed under S4 Hormone and Metabolic Modulators. Prohibited in-competition and out-of-competition for all athletes.
Legal to purchase and use for legitimate laboratory research. Must be labeled 'for research use only.' Not for human administration.
Related Research Guides
Frequently Asked Questions
What is Melanotan II?
Melanotan II (MT-II) is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone (α-MSH). It is a non-selective melanocortin receptor agonist that activates MC1R (producing skin tanning), MC3R and MC4R (producing appetite suppression and sexual effects), and MC5R. It was developed at the University of Arizona in the 1990s as part of research into skin pigmentation and photoprotection.
Is Melanotan II FDA-approved?
No. Melanotan II is not FDA-approved for any indication. The FDA has issued warning letters to distributors selling MT-II for human use. It is sold legally for laboratory research purposes only. Bremelanotide (Vyleesi), a related but distinct melanocortin analogue, received FDA approval in 2019 for hypoactive sexual desire disorder — but it is a different compound with different receptor selectivity and pharmacokinetics.
What is the difference between Melanotan II and PT-141?
PT-141 (bremelanotide) is a metabolite of Melanotan II and a related but distinct compound. It has greater selectivity for MC3R and MC4R (sexual function) and reduced activity at MC1R (tanning). PT-141 was developed specifically to isolate the sexual dysfunction effects while minimizing the tanning and nausea side effects of MT-II. PT-141 received FDA approval as Vyleesi in 2019; MT-II has not.
What are the main side effects of Melanotan II?
The most common adverse effect in clinical trials is nausea, occurring in over 50% of subjects. Other common effects include facial flushing, spontaneous erections in males, darkening of existing moles (melanocytic nevi), and diffuse hyperpigmentation. Theoretical concerns include melanoma risk due to MC1R activation, though no definitive causal data exists in humans. The FDA warning letters cite concerns about these safety risks in the context of unregulated human use.
What is Melanotan II used for in research?
Research applications of MT-II include: melanocortin receptor pharmacology (characterizing MC1R–MC5R binding and signaling), photoprotection research (whether pre-tanning reduces UV-induced DNA damage), obesity and appetite regulation (MC4R-mediated satiety signaling), sexual dysfunction models (MC3R/MC4R pro-erectile pathways), and melanoma biology (the role of MC1R in melanogenesis and malignant transformation).
Is Melanotan II the same as the 'Barbie drug'?
Yes — Melanotan II is commonly referred to as the 'Barbie drug' or 'Barbie jab' in media coverage, particularly in the UK and Australia, where it has been widely used for cosmetic tanning. The nickname refers to its use for achieving a tanned appearance. Both the FDA (US) and the MHRA (UK) have issued warnings about its unregulated use due to safety concerns including nausea, mole changes, and unknown long-term risks.
Research MT-2 at Purgo Labs
Third-party tested, ≥99% purity, COA with every batch.
How to Reconstitute Melanotan II
Melanotan II reconstitutes in bacteriostatic water (BAC water). For a 10mg vial, add 2mL BAC water for a 5mg/mL solution. Stable for 4 weeks refrigerated. Use a 27–31G insulin syringe for subcutaneous administration. First-dose nausea is common — start with a lower volume.