PT-141 (bremelanotide): what the RECONNECT trials found, and what they didn’t

PT-141, now called bremelanotide, is one of the few peptides on the “research” market that is also a real, approved medicine. The FDA approved it in 2019 as Vyleesi, an on-demand injection for premenopausal women with persistent, distressing low sexual desire [1,2]. Two phase 3 trials in 1,267 women showed statistically clear but modest gains in desire and less distress, no increase in satisfying sexual events, and nausea in 40% of women taking it [2,3].

What PT-141 is

Bremelanotide is a small ring-shaped peptide built on the core of α-melanocyte-stimulating hormone (α-MSH), the hormone that also controls skin pigment. It grew out of the University of Arizona’s melanotan programme: Hadley and Dorr describe it as “a new MTII analog”, a close relative of Melanotan II, developed by Palatin Technologies [6]. Melanotan II itself had already been tested clinically for erectile dysfunction [6]. Its own record, and the legal position it sits in, are covered in our melanotan guide.

Bremelanotide activates melanocortin receptors, with high affinity for the type 4 receptor (MC4R) in the brain, which is thought to be involved in sexual response [1]. The FDA label is candid that “the mechanism by which Vyleesi improves HSDD in women is unknown” [2]. It also binds MC1R on pigment cells, which explains one of its side effects: darkening of patches of skin [2].

The important difference from drugs such as sildenafil (Viagra) is where it works. Sildenafil acts on blood vessels in the genitals and needs sexual stimulation to have an effect. Bremelanotide is thought to act in the brain, which is why it was developed for desire rather than for mechanics.

Early studies in men

Palatin first tested PT-141 as an erectile dysfunction drug. In healthy men and men with mild-to-moderate erectile dysfunction who responded to Viagra, a nasal spray produced erections significantly more often than placebo at doses above 7 mg, with the first erection at around 30 minutes [7]. Injected under the skin, it produced erections in healthy men at doses above 1 mg and, at 4 or 6 mg, in men who hadn’t responded adequately to Viagra [8]. Flushing and nausea were the commonest side effects [7].

A 2008 Iranian trial reported that bremelanotide rescued men who had failed on sildenafil [9]. In 2023 the Journal of Urology published an expression of concern about that paper [10], so we don’t rely on it. Bremelanotide isn’t approved for men [2]; the approved product came out of the later programme in women.

The human evidence in women

A phase 2b dose-finding trial in premenopausal women with sexual dysfunction randomised participants to placebo or 0.75, 1.25 or 1.75 mg injections used as desired over 12 weeks (efficacy data for 327 women) [5]. At the two higher doses combined, satisfying sexual events rose by 0.7 a month against 0.2 on placebo (p = 0.018), with improvements in sexual function and distress scores [5].

That led to the two phase 3 RECONNECT trials.

The approved label tells women to inject at least 45 minutes before anticipated sex and not more than once in 24 hours [2]. The trials had two co-primary outcomes: the desire domain of the Female Sexual Function Index and one item on the Female Sexual Distress Scale that asks how bothered a woman is by low desire [3].

Numbers from Kingsberg et al. [3].

What do those numbers mean? The desire domain is scored from 1.2 to 6, and the distress item from 0 to 4 [2]. So the average extra gain over placebo was well under half a point on each. The FDA label adds context the journal abstract doesn’t: the number of satisfying sexual events, a secondary endpoint, did not differ significantly between bremelanotide and placebo [2]. And far more women stopped bremelanotide early (40% vs 13% in one trial, 39% vs 25% in the other) [2]. Because more women dropped out on the drug, the FDA added an exploratory analysis counting only those who finished treatment and improved; it used a responder threshold of at least 1.2 points on the desire score [2].

The trials were funded by Palatin and its licensing partner AMAG Pharmaceuticals, and company employees were among the authors [3].

Who was in the trials

The women averaged 39 years old, 85.6% were white and 96.6% were enrolled at US sites [3]. Everyone had a diagnosis of hypoactive sexual desire disorder, which by definition means low desire that causes marked distress and isn’t explained by another medical or psychiatric condition, relationship problems or a medication [2]. That’s a narrow group. The results don’t tell you what bremelanotide does for women whose low desire has an obvious cause, for women after the menopause, or for people with normal desire who want more of it. The label spells this out by excluding enhancement of sexual performance from the approved uses [2].

The trial design also matters. Because the drug is taken on demand rather than daily, how often women used it varied; the label notes most used it two to three times a month and no more than once a week [2]. Effects that show up with occasional use may not predict what happens with frequent use, and frequent use is exactly when skin darkening becomes more common.

A year of open-label use

Of the 856 women who completed the core trials, 684 entered a 52-week open-label extension where everyone got bremelanotide, and 272 finished it [4]. Among those who stayed, desire and distress scores kept improving, but with no placebo group and 60% dropping out, those figures describe the women who tolerated and liked the drug rather than everyone who tried it [4]. Nausea was reported by 40.4%, flushing by 20.6% and headache by 12.0% [4].

Safety and side effects reported

The FDA label is the most complete summary of harms [2]:

• Nausea. 40% on bremelanotide vs 1% on placebo in phase 3. It usually started within an hour and lasted about two hours; 13% needed anti-sickness medicine and 8% stopped because of it. It was most common after the first dose (21%), falling to about 3% with later doses.
• Blood pressure. Each dose raised blood pressure by up to 6 mmHg systolic and 3 mmHg diastolic, peaking 2 to 4 hours after the injection, with heart rate falling by up to 5 beats a minute. Levels usually returned to baseline within 12 hours. The drug is contraindicated in uncontrolled high blood pressure or known cardiovascular disease.
• Skin darkening. Focal hyperpigmentation of the face, gums or breasts occurred in 1% of women using up to 8 doses a month. In a separate study with daily dosing, 38% developed it within 8 days, it was more likely in darker skin, and it didn’t always fade after stopping.
• Interactions. It may slow stomach emptying and can markedly reduce levels of oral naltrexone, used for alcohol and opioid dependence.

The label recommends no more than 8 doses a month [2]. We report that as the approved limit, not as a guide.

Legal and regulatory status

In the US, Vyleesi is a prescription medicine approved in 2019 for premenopausal women with acquired, generalised hypoactive sexual desire disorder that isn’t caused by another medical or psychiatric condition, relationship problems or medication [2]. The label says it isn’t indicated for postmenopausal women or men, or “to enhance sexual performance” [2]. We found no marketing authorisation for bremelanotide in the UK or from the European Medicines Agency. Nasal sprays and vials sold online as “PT-141” are not the approved product and aren’t made to medicine standards.

What is still open

• Whether the modest average gain in desire is meaningful to most women, given no change in satisfying sexual events.
• How it performs in postmenopausal women and in men, where it isn’t approved.
• Long-term effects of repeated blood-pressure rises in people with borderline cardiovascular risk.
• Whether skin darkening from frequent use is permanent.
• What unregulated “PT-141” products actually contain.

What this means

Bremelanotide is the test case this library has been missing: a peptide that actually cleared the bar. It got a sponsor, a licensable indication and two phase 3 trials, and what that bought is a medicine that works a little. A 0.35-point average gain in desire, with no significant rise in satisfying sexual events, is a real effect [3], but it sits close to the edge of what a woman would notice. We would rather say that plainly than dress it up.

The open questions are still open for a specific reason, and it is not the one that applies to peptides nobody can patent. Palatin owned bremelanotide, trialled it and licensed it; the drug was never orphaned. What was never funded is everything outside the commercial case. A phase 3 in men, in postmenopausal women, or in people with normal desire who want more would cost tens of millions and buy an indication the sponsor did not need in order to sell the product it already had. When a label says “not indicated for men” [2], that is a business boundary, not a scientific verdict.

So the practical position is narrow and clear. Vyleesi is a real medicine, with a modest effect on desire and a side-effect profile a woman and her prescriber should weigh together: nausea in 40%, blood-pressure rises, and skin darkening that may not fade [2,4]. A vial sold online as “PT-141” is not a cheaper version of the same thing. It carries no proven dose, no sterility or endotoxin testing, no guarantee of strength, and the trial evidence above was generated in women injecting the approved product, not in anyone using a grey-market vial. If bremelanotide is what you want, the approved injection is the only form of it that has been measured in people.

We are not going to pretend the gap here mirrors the one around compounds no company can own. Bremelanotide was owned, trialled and approved; the gaps that remain are the ones the market chose not to fill, and that is a different problem, with a different kind of answer.

Educational content only — not medical advice. Many peptides discussed on HPR are not approved for human use. Talk to a qualified clinician before making any decision about your health.