Who discovered PT-141? No single inventor gets the credit. PT-141 grew out of melanotan II, a tanning peptide that chemist Victor Hruby, cell biologist Mac Hadley and their colleagues designed at the University of Arizona in the late 1980s. In its first human test, reported in 1996 by pharmacologist Robert Dorr's team, the three male volunteers had spontaneous erections nobody had set out to cause. Palatin Technologies, a New Jersey drug company, then developed a close relative of that molecule under the code PT-141. Its generic name is bremelanotide, and in 2019 it was approved as Vyleesi for one narrow group of women.
Who discovered PT-141?
The Arizona group wasn't looking for a sex drug. They were studying alpha-MSH (alpha-melanocyte-stimulating hormone), a small hormone that tells pigment cells to make melanin, the brown pigment behind a tan. The hope was a tan without the sun, which the team thought might lower the risk of skin cancer.
The chemists set out to build longer-lasting versions of the hormone. In 1980, Sawyer, Hruby, Hadley and colleagues reported a version with two altered amino acids (amino acids are the building blocks of proteins) that resisted breakdown and was 26 times as potent as the natural hormone in one lab test. That straight-chain molecule became known as melanotan I. In a 1991 JAMA trial of 28 healthy men, those given ten injections of it over 12 days developed darker skin; those given a salt-water placebo did not.
In 1989 the same lab published a set of smaller, ring-shaped versions, first tested on frog and lizard skin. One of them, a ring of seven amino acids, became melanotan II. By 1994, university pharmacy researchers described it as a peptide "currently being evaluated for the prevention of sunlight-induced skin cancers" (Lan et al., 1994).
How was PT-141 discovered? A side effect in three men
Dorr's 1996 pilot was tiny: three healthy men got low-dose injections under the skin over two weeks, to check safety and tanning. Two of the three did tan.
But the paper also recorded something else. Stretching and yawning "appeared to correlate with the onset of spontaneous, penile erections," which came and went for one to five hours after a dose. Mild nausea showed up at most dose levels.
The Arizona team followed the clue. In a 1998 study, Wessells and colleagues compared melanotan II with a placebo in ten men whose erectile dysfunction had no known physical cause; eight of the ten developed erections on the drug. A 2000 follow-up in ten men with physical risk factors saw erections after 12 of 19 injections, against 1 of 21 placebo doses, and the men reported more sexual desire.
That last finding pointed the way: the authors wrote that it "warrants further investigation of centrally acting agents on disorders of sexual desire", meaning drugs that act in the brain rather than on blood vessels. How PT-141 works covers that brain pathway in detail.
How PT-141 got its name
The names come in layers. Melanotan I and melanotan II are the names the Arizona researchers used for their straight-chain and ring-shaped molecules, as Hadley and Dorr recounted in 2006. The same history calls PT-141 "a new MTII analog" from Palatin Technologies, an analog being a deliberately modified copy. PT-141 was Palatin's development code.
Bremelanotide is the generic name, the official non-brand name. Both molecules are the same ring of seven amino acids; melanotan II ends in an amide group, while the Vyleesi label describes bremelanotide as ending in a free acid.
Even the brand changed. When AMAG Pharmaceuticals licensed North American rights in January 2017, the announcement used the name Rekynda. It reached pharmacies as Vyleesi.
Melanotan I took its own road: its sequence is afamelanotide, the active ingredient in Scenesse, an implant approved in the U.S. on October 8, 2019 for a rare disorder that makes sunlight painful.
From nasal spray to injection: bremelanotide history
Palatin started with men and a nasal spray. Its scientists reported in 2003 that PT-141 produced a rapid, dose-dependent increase in erectile activity in healthy men and men with erectile dysfunction, and King Pharmaceuticals later joined as a partner. The PT-141 nasal spray page follows that route.
Then came the turn. On August 30, 2007, Palatin and King said they had delayed phase 3 trials for erectile dysfunction after FDA "questioned the overall efficacy results" and "cited blood pressure increases as its greatest safety concern." King gave notice that September and the partnership ended that December.
The women's program was already running. FDA's review of the drug dates its FDA research file (the filing that allows testing in people) to 2001 and says the first studies in women also used the nose. Because the amount reaching the bloodstream varied too much by that route, development moved to a 1.75 mg injection under the skin.
A dose-finding trial that analyzed 327 premenopausal women came next. Then two phase 3 trials called RECONNECT, which began in January 2015, enrolled 1,267 premenopausal women with distressing low desire (Kingsberg et al., 2019). In those 24-week trials, desire scores rose and distress scores fell more with the as-needed injection than with placebo, and nausea, flushing and headache were more common. The drug was approved as Vyleesi on June 21, 2019.
The other branch: melanotan II went online
Melanotan II never became an approved medicine. Within a week of the Palatin announcement, FDA posted a September 5, 2007 consumer update advising people to stop using melanotan II, which was being sold online as a tanning agent with claims about skin cancer and rosacea. The agency said the product had no approved application.
FDA's page on compounding ingredients that may carry significant safety risks lists melanotan II and cites published case reports including melanoma, a brain-swelling syndrome and priapism, an erection that won't subside. An FDA advisory committee is due to discuss whether compounding pharmacies may use it, at a meeting before the end of February 2027 (meeting page, current as of April 15, 2026). Melanotan 2 side effects covers that record.
Where PT-141 stands today
As of September 23, 2026, the day this article was written, Vyleesi is still marketed. Drugs@FDA lists Cosette as the holder of its application, and the DailyMed label, marked "Revised: 3/2024", limits it to premenopausal women with acquired, generalized hypoactive sexual desire disorder. The label says it is not for postmenopausal women, for men or for enhancing sexual performance.
The gray market has kept pace with the name. On August 24, 2026, FDA sent a warning letter to an online peptide seller; it named the seller's "PT-141 (Bremelanotide)" among products the agency called unapproved new drugs.
The whole path, from frog skin to pharmacy shelf:
| Year | Milestone |
|---|---|
| 1980 | Arizona team reports the long-acting molecule later called melanotan I |
| 1989 | Ring-shaped versions published; one becomes melanotan II |
| 1996 | First human study of melanotan II records spontaneous erections |
| 2007 | FDA raises efficacy and blood-pressure concerns; phase 3 plans for men delayed |
| 2015–2016 | RECONNECT phase 3 trials in 1,267 women |
| 2019 | Vyleesi approved on June 21 |
| 2023 | Palatin sells Vyleesi to Cosette Pharmaceuticals |
What the history means for a prescription
One branch of this family went through trials, a label and a prescriber; the other went into vials sold online without a prescription.
PT-141 through Promise is dispensed as a compounded medication, which is different from an FDA-approved product: the formulation offered here is not FDA-approved. A licensed provider may still prescribe a compounded formulation; that decision is between the patient and the doctor. At Promise, a licensed provider reviews every request, and not everyone qualifies. If PT-141 is prescribed, a licensed U.S. compounding pharmacy prepares it for that one patient, with a pharmacy label and a record for follow-up.
