What are PT-141 (bremelanotide) and melanotan II?

What they are

Bremelanotide and melanotan II are lab-made peptides, short chains of amino acids, the building blocks of proteins. Both mimic alpha-melanocyte-stimulating hormone (alpha-MSH), one of a family of hormones called melanocortins. Bremelanotide, also called PT-141, is FDA-approved for one use in women. Melanotan II is not approved for any use and has been sold online as a tanning injection.^{1,2,3,4,5,6,7}

Both are chains of seven amino acids that differ only in a small group of atoms at one end, according to the FDA’s substance records.^4,5,8

Researchers at the University of Arizona made melanotan II and tested it in people as a tanning drug in the 1990s. Bremelanotide is a newer, slightly altered version of it (an analog), developed for sexual problems.^1,3

Melanotan I, now called afamelanotide, is a different peptide. Since 2019 it has been FDA-approved as an implant to increase pain-free time in light for adults with erythropoietic protoporphyria, a rare disorder.^9,10,11

How they work

Both act on melanocortin receptors, docking sites on cells that respond to alpha-MSH. Bremelanotide activates several of the five types. At the approved dose, two matter most: MC1R, on pigment cells, explains the skin darkening it can cause, and MC4R is on nerve cells in the brain and spinal cord. How it works in the condition it is approved for is unknown, its label says.^2,4

Melanotan II also acts on several melanocortin receptors. In small studies in the 1990s, it darkened the skin and caused spontaneous erections.^3,14,15,22

How they are taken

Bremelanotide is approved as an injection under the skin of the belly or thigh, from a single-dose prefilled pen (an autoinjector). It is used as needed before expected sexual activity. Its label advises against frequent use, which was rarely tested, makes skin darkening likelier and keeps blood pressure raised for longer each month.⁴

Early bremelanotide studies in women used a nasal spray, but absorption through the nose varied, so the developer switched to injections, the FDA’s review notes. Melanotan II has been injected under the skin in studies and sold online in vials for injection; a 2025 case report describes a nasal spray.^2,3,15,7,23

What the research in people shows

Bremelanotide’s approval rests on two identical randomized trials, called RECONNECT, published in 2019. They enrolled 1,267 premenopausal women with acquired, generalized hypoactive sexual desire disorder. This is low desire, whatever the situation or partner, that began after a time of normal desire, causes marked distress or relationship strain, and has no other cause.^13,4,2

Women were assigned by chance to bremelanotide or a placebo, a dummy injection, and used it as needed for 24 weeks. In both trials, those on bremelanotide reported a larger rise in desire, and a larger fall in distress about low desire, than those on placebo. The FDA’s review called these “modest improvements”. Satisfying sexual events did not increase more than on placebo, a measure the FDA does not require for this condition.^13,4,2

Both trials were funded by the drug’s developers. About 4 in 10 women on bremelanotide stopped before 24 weeks, its label says. On placebo, about 1 in 8 stopped early in one trial and 1 in 4 in the other.^13,4

After the trials, 684 women took bremelanotide for up to 52 more weeks, knowing they were on it, and 272 finished. The authors reported no new safety concerns. With no comparison group, this extension cannot separate the drug’s effect from a placebo effect.²⁴

An outside researcher’s 2021 reanalysis of the trial data in the FDA application concluded that the drug is generally not useful. It cited modest benefits, and that women on placebo were likelier to finish the trial and join the extension. The trial authors published a reply disputing it. A 2024 analysis led by the same researcher found that results for 8 of the 11 efficacy outcomes it counted in the trials’ registry records had not been published.^25,26,27

No FDA approval covers men: development for erectile dysfunction did not lead to an approved product, the FDA’s 2019 review notes. A 2008 randomized trial in Iran gave a bremelanotide or placebo nasal spray to 342 men whom sildenafil, a common erection pill, had not helped. It reported more improvement, and more side effects, with bremelanotide. In 2023 its journal issued an expression of concern, a formal notice that questions have been raised.^4,2,28,29

A 2026 systematic review, which gathers all eligible studies by set rules, found 12 studies of peptides for male sexual problems. Melanocortin drugs such as bremelanotide and melanotan II showed the most consistent improvements in erections. But the authors wrote that the studies were small and short, and the evidence too limited for routine care.³⁰

In a 1996 pilot study, melanotan II’s developers gave three healthy men injections of it, alternating with salt water, for two weeks. They recorded spontaneous erections, nausea, yawning and darker skin. Two later trials, in 1998 and 2000, each gave 10 men with erectile dysfunction melanotan II and a placebo in turn, and found more erections after melanotan II. In the 2000 trial, men also reported more desire, and severe nausea followed 4 of 19 injections.^3,14,15

Side effects and risks

Nausea was most common after the first dose and usually lasted about two hours. It led 13 in 100 women to take anti-nausea medicine and 8 in 100 to leave the trials. Taking the anti-nausea drug ondansetron beforehand did not reduce it in a study of 228 healthy women. Serious side effects were reported in about 1 in 100 women on bremelanotide and 1 in 200 on placebo.⁴

Melanotan II’s side effects are known mostly from case reports, accounts of single patients that cannot show a drug caused a problem. The FDA cites case reports of melanoma, a skin cancer; a brain disorder called posterior reversible encephalopathy syndrome; stimulant-like poisoning; and priapism, an erection lasting hours. It also says compounded melanotan II may provoke an immune response by some routes, because the peptide can clump or carry impurities.^16,31,32

A 2017 review found reports of new moles and changes in existing moles in melanotan users, including four cases of melanoma arising in existing moles during or soon after use. It said conclusive evidence of a link was lacking.³¹

In a 2015 lab study, melanotan II vials from three online shops all held less than claimed, and vials from two held unidentified impurities.⁷

FDA status

The FDA approved bremelanotide on June 21, 2019. Its latest label change, approved on October 22, 2026, added a breastfeeding study. The label says it is for premenopausal women with acquired, generalized hypoactive sexual desire disorder, and not for women after menopause, for men or to enhance sexual performance. Any other bremelanotide product, including a compounded one, is not FDA-approved.^12,37,4,38

Flibanserin, a daily bedtime pill, is the one other FDA-approved medicine for this condition. Since December 2025 its label has covered women under 65, including after menopause. It carries a boxed warning, the FDA’s most serious kind, about severe low blood pressure and fainting with alcohol, certain other medicines or liver disease.³⁹

In warning letters dated August 24, 2026, the FDA told companies selling peptides online, often labeled for research use, that their “PT-141” products were unapproved new drugs. These are drugs sold without the FDA approval the law requires.^40,41

No drug containing melanotan II is FDA-approved. In 2007 the FDA told a US company selling it online for tanning that it was an unapproved new drug. An FDA import alert lets the agency detain shipments without examining them. It has listed products sold as melanotan I and II from named firms since 2010, and PT-141 from one Canadian firm since 2020.^6,43,42

Compounded versions

Compounded drugs are not FDA-approved, which means the FDA does not review their safety, effectiveness or quality before they are sold. Section 503A of federal drug law covers state-licensed pharmacies that compound for individual patients’ prescriptions. They may use bremelanotide acetate, the form in the approved injection, because it is part of an FDA-approved drug.^{38,21,17,12,4}

Because that injection is on the market, a 503A pharmacy may not regularly or in large amounts compound essentially a copy of it. The exception is a change the prescriber records as making a “significant difference” for the patient; a lower price does not count. Outsourcing facilities (FDA-registered 503B compounders) may not make it from the raw ingredient: it is on neither the FDA’s list of raw ingredients with a clinical need nor its shortage list. Bremelanotide’s trials tested only the approved injection, not a compounded version.^{18,12,44,45,46,4,13}

Melanotan II is not part of any FDA-approved drug and is not on the FDA’s list of extra ingredients 503A pharmacies may use (the 503A bulks list). From September 29, 2023, it was in Category 2: ingredients proposed for compounding (nominated) that the FDA flagged for safety risks. Its nominators later withdrew it, and the FDA’s page, updated April 22, 2026, lists it as withdrawn with the same safety summary.^{6,19,47,17,16}

It is now in none of the FDA’s categories, so the FDA’s interim policy for nominated ingredients under review does not cover it. Nor does the draft policy published in October 2026 by the Department of Health and Human Services (HHS), the FDA’s parent department. In it, HHS says it does not intend to take enforcement action against 503A compounding with six other peptides, if ten conditions are all met.^20,17,38,21

An FDA page says its Pharmacy Compounding Advisory Committee, a panel of outside experts, will discuss adding melanotan II to the 503A bulks list before the end of February 2027. The page, last updated on April 15, 2026, a week before the FDA listed the withdrawal, gives no meeting date.^48,16

What isn’t known

How long each bremelanotide dose works is unknown, its label says. The trials lasted 24 weeks and the uncontrolled extension 52 more, so effects over years are unknown. The trial authors wrote that safety and benefit were not established in women after menopause, in women taking psychiatric medicine, or in groups other than the mostly white, non-Hispanic women studied.^4,13,24

How often melanotan II users develop melanoma or other harms is not known. The 2014 and 2026 patients also used tanning beds, so those reports cannot separate the drug’s effects from the tanning beds’ effects.^33,32,31

Questions to ask a clinician