Melanotan II (MT-II) is a synthetic peptide modeled on alpha-melanocyte-stimulating hormone (α-MSH), the hormone that tells pigment cells to make melanin. University of Arizona researchers designed it in the late 1980s as a “sunless tanning” agent. In small early human studies it also caused spontaneous erections, so it was briefly studied for erectile dysfunction.

Melanotan II has never been approved as a medicine by the FDA, the UK MHRA or Australia’s TGA. It is sold illegally online as tanning injections and nasal sprays. Regulators in all three countries have warned against it, and case reports link it to changes in moles, melanoma, priapism, rhabdomyolysis and kidney injury.

This page summarizes what the early studies, regulators and published case reports describe. It is for education only and is not medical advice.

Property	Detail
Class	Synthetic cyclic peptide; non-selective melanocortin receptor agonist
Origin	University of Arizona, described in 1989
Approval status	Never approved; FDA treats it as an unapproved new drug; not on Australia’s ARTG; unauthorised in the UK
Formula / weight	C₅₀H₆₉N₁₅O₉; 1024.2 g/mol (PubChem)
Human evidence	One pilot phase I study (3 men) and two small crossover trials in erectile dysfunction (10 men each), all from the 1990s
Half-life	No published human pharmacokinetic data found
Illicit forms	Powder for injection; nasal sprays
Related approved drug	Bremelanotide (Vyleesi), an MT-II analog, FDA-approved in 2019 for a sexual desire disorder in premenopausal women
WADA 2026	Not named; S0 covers unapproved substances not listed elsewhere

What it is

Natural α-MSH is a 13-amino-acid peptide. Melanotan II is a shortened, ring-shaped (cyclic) version built from α-MSH positions 4–10, a stretch of seven amino acids. Researchers made three main changes (Dorr et al., Life Sci 1996):

replaced methionine at position 4 with norleucine;
used the mirror-image D-form of phenylalanine at position 7;
joined positions 5 and 10 with a lactam bridge, which closes the ring.

The designers described the resulting analogs as superpotent, prolonged acting and resistant to breakdown by enzymes (Hadley and Dorr, Peptides 2006).

PubChem lists its formula as C₅₀H₆₉N₁₅O₉ and its molecular weight as 1024.2 g/mol (PubChem CID 92432).

Origin

Al-Obeidi, Hruby, Hadley and colleagues at the University of Arizona reported a series of cyclic lactam α-MSH analogs in 1989 (Al-Obeidi et al., J Med Chem 1989). In a lizard-skin assay (animal tissue, not humans), the seven-residue analog that became MT-II darkened skin cells about 90 times more potently than α-MSH. The paper described the series as potent and prolonged acting.

The same team patented two analogs (Hadley and Dorr, Peptides 2006):

Analog	Shape	Main clinical direction
Melanotan I	Linear, full-length α-MSH analog	Skin tanning
Melanotan II	Cyclic, shortened analog	Erectile dysfunction
PT-141 (bremelanotide)	MT-II analog developed by Palatin Technologies	Sexual dysfunction

Melanotan I has its own page: Melanotan I. Bremelanotide is covered at PT-141 (bremelanotide).

How it works

Melanotan II switches on several melanocortin receptors rather than one (Wessells et al., Int J Impot Res 2000). The FDA label for its analog bremelanotide explains what these receptors do (Vyleesi label):

MC1R sits on melanocytes (pigment cells). Activating it increases melanin and darkens skin.
MC4R is found on nerve cells in many areas of the brain.

Case-report authors attribute the sexual effects of melanotan to MC3 and MC4 receptors in the brain, and its tanning to MC1R in the skin (Mallory et al., Sex Med 2021). Acting on several receptors at once is thought to be why tanning, erections, nausea, yawning and reduced appetite tend to appear together. It also means MT-II acts on moles, which are clusters of melanocytes.

How it behaves in the body

No human pharmacokinetic study of Melanotan II has been published that we could find, so its half-life in people is unknown. Published kinetic work is limited to rats given intravenous doses (Ugwu et al., Biopharm Drug Dispos 1994), and those figures should not be applied to people.

In the 1996 pilot study, spontaneous erections came and went for 1–5 hours after each dose, and darker skin was still measurable one week after dosing stopped (Dorr et al., Life Sci 1996).

Regulatory status

Melanotan II is not an approved medicine in the US, the UK or Australia. Regulators have acted mainly against sellers.

United States (FDA)

2007 warning letter. FDA sent a warning letter to a Tennessee company, Melanocorp, on or about August 30, 2007. The company had marketed MT-II online as an injectable tanning product. FDA stated that MT-II was a new drug that could not be sold across state lines without an approved application (FDA notice, 2016).
Criminal conviction. The company kept shipping MT-II from about September 2007 to April 2009. Its owner pleaded guilty in 2015 to two counts of conspiracy in federal court, and in 2016 FDA proposed to permanently debar him from providing services to companies with FDA drug applications (same source).
Compounding. FDA’s list of bulk substances that may present significant safety risks includes Melanotan II among nominations that were withdrawn. FDA’s summary states that compounded MT-II may carry a risk of immune reactions from peptide clumping or impurities. It adds that published case reports describe “melanoma, posterior reversible encephalopathy syndrome, sympathomimetic toxidrome and priapism” (FDA).

United Kingdom (MHRA)

In a 2024 Freedom of Information response, the MHRA explained how it classifies these products (MHRA FOI 24/274):

Injectable and pen products containing MT-II are medicines. Nasal sprays count as medicines only if they are sold with claims to treat or prevent disease.
Selling, supplying or advertising unauthorised medicines is not permitted under the Human Medicines Regulations.
The agency has removed melanotan products from the market for over 10 years.
It received 16 UK suspected adverse reaction reports for MT-II between 2012 and 2022. It advises anyone using MT-II injections or nasal sprays to stop immediately.

Australia (TGA)

The TGA’s 2017 consumer alert said Melanotan I and II are prescription-only medicines that are not on the Australian Register of Therapeutic Goods (ARTG). It is unlawful to import them for personal use without a prescription from an Australian doctor. The alert listed darkened skin, moles and freckles, nausea, vomiting, loss of appetite, spontaneous erections, facial flushing, and stretching and yawning as side effects (TGA, 2017).

A 2025 TGA warning said melanotan is not approved for sale or use as a tanning agent in Australia (TGA, 2025). It also said:

It is illegal to supply melanotan without a doctor’s prescription in any form, including sprays, tablets, injections and creams. It is also illegal to advertise it, including through social media influencers.
MT-II has been linked to reports of more moles and freckles, kidney dysfunction and brain swelling. The TGA called skin cancer the most concerning risk.
A melanotan tan does not protect against UV damage the way sunscreen does.

Other countries and sport

A 2017 review noted that several national health agencies have issued safety warnings about Melanotan I and II (Habbema et al., Int J Dermatol 2017).

The 2026 WADA Prohibited List does not name Melanotan II. Its S0 class bans at all times any pharmacological substance that is not covered by other sections and has no current approval for human therapeutic use (WADA 2026 Prohibited List).

What the research shows

All controlled human data come from the University of Arizona group in the 1990s. Studies were tiny and short, and none was designed to measure long-term safety.

Tanning (pilot phase I)

Three healthy men received MT-II or saline on alternating days in a single-blind pilot study over two weeks (Dorr et al., Life Sci 1996). Findings:

Two of the three men had measurably darker skin on the face, upper body and buttocks one week after dosing ended.
Mild nausea occurred at most dose levels.
A stretching-and-yawning complex accompanied spontaneous erections lasting 1–5 hours.
At the highest dose tested, one of two men developed WHO grade II sleepiness and fatigue.

Erectile dysfunction

The erections seen in the tanning study led to two double-blind, placebo-controlled crossover trials, monitored with RigiScan (a device that records penile rigidity) over 6 hours.

Trial	Men	Result with MT-II	Result with placebo
Psychogenic ED (Wessells et al., J Urol 1998)	10	Erections in 8 of 10; tip rigidity over 80% for 38.0 min	Tip rigidity over 80% for 3.0 min (p = 0.0045)
Pooled psychogenic and organic ED (Wessells et al., Int J Impot Res 2000)	20	Erections in 17 of 20; increased sexual desire after 68% of doses	Increased desire after 19% of doses (p under 0.01)

Nausea and yawning were common. In the pooled analysis, 12.9% of subjects had severe nausea. The later commercial program focused on the analog PT-141 (bremelanotide) (Hadley and Dorr, Peptides 2006).

Side effects and risks

No trial has tested Melanotan II for safety over months or years. What is known comes from the small 1990s studies, regulators’ adverse event reports, and case reports in people using illicit products. A case report shows that an event happened after MT-II use. It cannot prove that MT-II caused it, and many patients also used sunbeds or other drugs.

Common effects in studies

In the controlled studies, the common effects were nausea (sometimes severe), stretching and yawning, reduced appetite, spontaneous erections, and sleepiness or fatigue at the highest dose (Dorr et al., Life Sci 1996; Wessells et al., J Urol 1998). The TGA also lists vomiting and facial flushing (TGA, 2017).

Moles, new nevi and melanoma

Because MT-II stimulates melanocytes, dermatologists have reported changes in moles (melanocytic nevi):

Eruptive atypical nevi. A 40-year-old man with past melanoma and many dysplastic (irregular) nevi developed crops of new moles after using a synthetic α-MSH product. Many looked atypical under the microscope, and his existing moles darkened and grew. They gradually lightened after he stopped (Cardones and Grichnik, Arch Dermatol 2009).
Rapid onset. A German report described new moles and darkening of existing moles within 24 hours of a single MT-II injection (Schulze et al., Eur J Dermatol 2014).
Melanoma. A 20-year-old woman with fair skin, seen in Denmark, was diagnosed with melanoma three months after a 3–4 week course of MT-II injections combined with sunbed use (Hjuler and Lorentzen, Dermatology 2014).
Mucosal melanoma. A 22-year-old woman in the UK developed a mucosal melanoma in the front of the upper jaw after using an MT-II nasal spray to tan (Yassin Alsabbagh et al., Int J Oral Maxillofac Surg 2025).

A 2017 review counted four published cases of melanoma arising from existing moles during or shortly after melanotan use. It concluded that conclusive evidence of a causal link is lacking (Habbema et al., Int J Dermatol 2017).

Priapism

Priapism is an erection lasting more than 4 hours. The ischemic (low-flow) type is a medical emergency, because trapped blood can scar the erectile tissue.

A man treated in Glasgow developed low-flow priapism after an abdominal MT-II injection. He needed blood drainage, flushing of the penis, and phenylephrine injections, and had not regained erectile function at 4 weeks (Dreyer et al., BMJ Case Rep 2019).
A 55-year-old man treated in Miami arrived with a 30-hour erection after an MT-II injection. Drainage and the maximum phenylephrine dose failed, so he needed surgery (penoscrotal decompression). At 15 weeks he had new erectile dysfunction with scarring. He had used MT-II yearly for 6 years without priapism before this episode (Mallory et al., Sex Med 2021).

Rhabdomyolysis and sympathomimetic toxicity

A 39-year-old man came to a Chicago emergency department two hours after injecting a large amount of internet-bought MT-II (Nelson et al., Clin Toxicol 2012). Mass spectrometry confirmed the product was MT-II. He had features of sympathomimetic excess (an adrenaline-like state), and rhabdomyolysis, a breakdown of muscle that can damage the kidneys:

Finding	Value
Heart rate	Up to 146 bpm
Other signs	Agitation, dilated pupils, sweating, muscle tremors
Creatine kinase (muscle enzyme)	1,760 IU/L on arrival; peak 17,773 IU/L
Creatinine (kidney marker)	2.25 mg/dL; improved to 1.23 mg/dL
Course	3 days in intensive care with IV fluids and bicarbonate

His urine drug screen was also positive for opiates.

Kidney infarction

Swedish nephrologists reported a renal infarction (death of kidney tissue from a blocked blood supply) that they judged most likely caused by MT-II. They proposed a clotting-related effect or direct kidney toxicity as possible mechanisms (Peters et al., CEN Case Rep 2020). The TGA also lists kidney dysfunction among reported harms (TGA, 2025).

Brain swelling (PRES)

Posterior reversible encephalopathy syndrome (PRES) is a form of brain swelling. A 2013 report linked PRES to melanotan use (Kaski et al., Ann Intern Med 2013), and FDA cites PRES among the serious events in published case reports (FDA).

Product quality and injection risks

Illicit products carry their own risks. A Danish lab analyzed MT-II vials bought from three online shops, each labeled as 10 mg (Breindahl et al., Drug Test Anal 2015):

vials held 4.32–8.84 mg of MT-II, well below the label;
vials from two of the shops contained 4.1–5.9% unknown impurities.

The TGA warns that self-injection can cause serious infection, and that the contents of unapproved products cannot be known from the label (TGA, 2017; TGA, 2025).

Key takeaways

Never an approved drug. Melanotan II was a 1980s university research peptide. It has not been approved by the FDA, MHRA or TGA, and FDA treats it as an unapproved new drug.
Acts on several receptors at once. It switches on melanocortin receptors in skin and brain, so tanning comes with nausea, yawning, appetite loss and spontaneous erections.
Human data are tiny and old. The published controlled studies included 23 men in total, and none studied long-term safety. Its human half-life is unknown.
Regulators actively warn against it. FDA pursued a seller to a criminal conviction, the MHRA has removed products for over a decade, and the TGA says supply without prescription and any advertising are illegal.
Serious harms are documented in case reports. These include new and darkening moles, melanoma, priapism needing surgery, rhabdomyolysis, renal infarction and brain swelling. Causation is unproven in individual cases.
Illicit products are unreliable. Tested vials contained about half the labeled amount, along with unknown impurities.

Sources

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Ugwu SO, Blanchard J, Nguyen LD, et al. A comparison of HPLC and bioassay methods for plasma melanotan-II (MT-II) determination: application to a pharmacokinetic study in rats. Biopharm Drug Dispos. 1994;15(5):383–390. PubMed.
Wessells H, Fuciarelli K, Hansen J, et al. Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction: double-blind, placebo controlled crossover study. J Urol. 1998;160(2):389–393. PubMed.
Wessells H, Levine N, Hadley ME, et al. Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with Melanotan II. Int J Impot Res. 2000;12(Suppl 4):S74–S79. PubMed.
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Melanotan II