PT-141

Origin and structure

Bremelanotide grew out of melanotan II, a synthetic analogue of α-melanocyte-stimulating hormone (α-MSH) made to darken the skin. In the first human test of melanotan II, published in 1996, three healthy men received injections of melanotan II and saline on alternating weekdays for two weeks. Two developed visible pigmentation, and spontaneous erections occurred one to five hours after dosing, together with bouts of stretching and yawning. That side effect is what turned a tanning compound into a lead for sexual dysfunction.

Palatin Technologies developed bremelanotide under the code PT-141. It is a ring of seven amino acids, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, identical to melanotan II except at one end, where it carries a free acid instead of an amide; its molecular weight is 1025.2. It was first tested in men with erectile dysfunction, both as a nasal spray and as an injection, before development moved to women. The phase 3 programme was funded by Palatin and AMAG Pharmaceuticals, and the US product is now marketed by Cosette Pharmaceuticals.

How it works

Bremelanotide switches on melanocortin receptors, the targets of α-MSH. It is not selective: in order of potency it acts on MC1R, MC4R, MC3R, MC5R and MC2R, and at the approved dose MC1R and MC4R matter most. MC4R sits on neurons in many parts of the brain and is the receptor linked to the effect on desire, although the FDA label states plainly that the mechanism in HSDD is unknown. MC1R sits on pigment cells, which is why some people develop dark patches. Sildenafil and related drugs act on blood flow in erectile tissue; bremelanotide acts through the nervous system.

After an injection under the skin, blood levels peak after about an hour, practically the whole dose is absorbed, and the half-life is about 2.7 hours (range 1.9 to 4.0).

The closest look at its effect in the brain comes from a small crossover study in London (Thurston 2022). Thirty-one premenopausal women with HSDD received 1.75 mg and placebo on separate occasions. After bremelanotide they reported more sexual desire for up to 24 hours, and brain scans while they viewed erotic images showed more activity in the cerebellum and supplementary motor area, less in the secondary somatosensory cortex, and stronger coupling between the amygdala and the insula. The authors read this as less self-consciousness and more sexual imagery; it is a single study of 31 women.

Is bremelanotide approved?

In the US, for one narrowly defined group of women. In the EU, no.

In the Netherlands bremelanotide is therefore not a registered medicine, and it may not be sold or advertised there as a medicine.

Research-grade PT-141, the lyophilised peptide sold for laboratory use, is not Vyleesi. It has no marketing authorisation anywhere, is not made under a medicines licence, and may not be used in people. The approval below covers the branded autoinjector only.

• EU: no marketing authorisation; the EMA has never authorised a bremelanotide medicine.
• US: approved on 21 June 2019 as a new molecular entity (NDA 210557) for premenopausal women with acquired, generalised HSDD: low desire that causes marked distress or difficulty in the relationship and is not caused by another medical or psychiatric condition, relationship problems, or a medicine or drug. The label excludes postmenopausal women and men and states that it is not for enhancing sexual performance. The current label, revised in October 2026, is held by Cosette Pharmaceuticals.

What the research shows

The approval rests on two identical phase 3 trials, RECONNECT studies 301 and 302, run in 2015 and 2016 almost entirely at US sites, and on one phase 2b dose-finding trial; all were sponsored by the companies developing the drug. In men there are only early studies and one larger trial whose paper now carries an expression of concern. The results:

• Phase 2b (Clayton 2016): 327 premenopausal women with sexual dysfunction self-injected 0.75, 1.25 or 1.75 mg or placebo for 12 weeks. On the pooled 1.25 and 1.75 mg doses, satisfying sexual events rose by 0.7 a month against 0.2 on placebo, the primary endpoint.
• RECONNECT (Kingsberg 2019): 1,267 women randomised to 1.75 mg or placebo for 24 weeks. On the FSFI desire score (range 1.2 to 6) bremelanotide gained 0.30 and 0.42 points more than placebo in the two trials, 0.35 combined; distress about low desire (scale 0 to 4) fell 0.33 points more. All differences were statistically significant.
• What did not change: in phase 3 the number of satisfying sexual events, a secondary endpoint, showed no significant difference from placebo (FDA label).
• Dropout: in one trial 40% of the bremelanotide group left the double-blind phase early against 13% on placebo, in the other 39% against 25%; 18% stopped because of adverse reactions, against 2%.
• Open-label extension (Simon 2019): 684 women continued on bremelanotide for up to 52 weeks and 272 finished. Desire scores in those treated from the start were 1.25 to 1.30 points above their original baseline, but without a control group this cannot be separated from a placebo response.
• Independent reanalysis (Spielmans and Ellefson 2024): 8 of the 11 efficacy outcomes registered for the trials had not been published; on those, effects ranged from nil to small. The authors also judged the evidence that the trial questionnaires measure what they claim to measure in women with HSDD to be questionable at best. The trial investigators rejected an earlier reanalysis by Spielmans as a failed meta-analysis (Kingsberg 2021).
• Men (Rosen 2004): in healthy men, single injections of 0.3 to 10 mg gave a statistically significant erectile response above 1 mg; in men who responded poorly to sildenafil, 4 and 6 mg beat placebo in a laboratory crossover with erotic video. No phase 3 trial in men has been published.
• Largest trial in men (Safarinejad 2008): 342 men who had not responded to sildenafil used a 10 mg nasal spray or placebo, and 33.5% against 8.5% had a positive response. In 2023 the journal attached an expression of concern to the paper, so the result should be treated with caution.

Side effects and warnings

Most side effects are short-lived and come within hours of a dose. In the phase 3 trials nausea affected 40% of women on bremelanotide against 1.3% on placebo; it usually began within an hour, lasted about two hours, and was most frequent after the first dose (21%), falling to about 3% with later doses. 13% needed an anti-nausea medicine and 8% left the trials because of it. Ondansetron given 30 minutes before the injection did not reduce it in a study of 228 healthy women. Flushing (20%), injection-site reactions (13%), headache (11%) and vomiting (5%) were the other frequent effects.

Blood pressure rises after every dose, by up to 6 mmHg systolic and 3 mmHg diastolic at two to four hours, while the heart rate drops by up to 5 beats a minute; both usually return to baseline within 12 hours. The label therefore rules it out in uncontrolled high blood pressure or known cardiovascular disease and allows no more than one dose in 24 hours.

Through MC1R, bremelanotide can darken patches of skin on the face, gums and breasts. This happened in 1% of women using up to eight doses a month, but in 38% of those given a dose every day for eight days, and the patches did not always fade after stopping; darker skin carried a higher risk.

Further label warnings: one case of acute hepatitis in the extension study, in which a role for the drug could not be excluded; slower stomach emptying, which can delay the uptake of oral medicines; a marked drop in the level of oral naltrexone; and harm to offspring in dog and mouse studies, which is why the label asks for effective contraception. The October 2026 label adds a study in 10 breastfeeding women: after a single 1.75 mg dose, the amount passed into breast milk was about 0.13% of the mother's weight-adjusted dose.

PT-141 versus melanotan II

The two peptides share the same ring of seven amino acids and differ only at one end. Both act on several melanocortin receptors at once, so both affect sexual response as well as skin pigment, and nausea is a common side effect of both.

The difference is in how far each was tested. Bremelanotide went through dose-finding and phase 3 trials and has an FDA label that quantifies its blood-pressure and pigmentation effects. Melanotan II was only tested in small early studies and has never been approved as a medicine by the EMA or the FDA.

Frequently asked questions

Is PT-141 the same as Vyleesi?

The same molecule, but not the same product. Vyleesi is a licensed autoinjector holding 1.75 mg of bremelanotide in 0.3 mL, made and tested under pharmaceutical rules and approved in the US for one group of women. PT-141 sold for research is the lyophilised peptide; its identity and purity are what a certificate of analysis says, nothing more, and it may not be used in people.

Does PT-141 work in men?

It produced erections in small laboratory studies: above 1 mg by injection in healthy men, and at 4 and 6 mg in men who responded poorly to sildenafil. There is no published phase 3 trial in men, the largest male trial carries an expression of concern from its journal, and the US label explicitly excludes men.

Is PT-141 legal in the Netherlands?

Bremelanotide has no marketing authorisation in the EU, so in the Netherlands it is not a registered medicine and may not be sold or advertised as a medicine. Buying and selling it as research material is a different status, which our guide on research-use-only products in the Netherlands explains.

Is PT-141 banned in sport?

No. Bremelanotide is not named on the WADA Prohibited List for 2026 or 2027, and because it is an approved medicine in the US it does not fall under class S0, which covers substances with no approval anywhere. It is also not in the 2027 monitoring programme. In the Netherlands the Dopingautoriteit works from the same list.

How long does PT-141 last?

Blood levels peak about an hour after an injection, and the half-life is about 2.7 hours. How long the effect on desire lasts is not established: the FDA label says the duration of effect after each dose is unknown, and in the London imaging study women reported more desire for up to 24 hours.

Storage and handling

Store according to product-label instructions and batch handling notes. Lyophilized research peptides are commonly kept dry, protected from light, and handled with clean laboratory technique.

References

Checked against these sources on 28 October 2026.

Related peptides