Bremelanotide
PT-141, bremelanotide acetate, PT 141, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH
Bremelanotide is a synthetic cyclic peptide analogue of alpha-melanocyte-stimulating hormone that acts mainly on the MC4 melanocortin receptor in the brain. It is one of the very few peptides in this library with genuine regulatory approval: the US FDA licensed it in 2019 for low sexual desire in premenopausal women. The approval rests on two large randomised trials whose statistical wins were real but whose effect sizes were modest.
Mechanism
Bremelanotide is a cyclic heptapeptide derived from alpha-MSH and is, chemically, the C-terminal deamidated (free acid) analogue of melanotan II. It is a non-selective melanocortin receptor agonist, with greatest potency at MC4R and MC1R, weaker activity at MC3R and MC5R, and negligible activity at the adrenal MC2R. Its effect on sexual desire is thought to be central rather than vascular. MC4R is densely expressed in the hypothalamic paraventricular nucleus and medial preoptic area and across the limbic forebrain; agonism there increases dopaminergic transmission in the medial preoptic area and shifts the excitatory-inhibitory balance in circuits that govern sexual motivation. This is a different pharmacology from PDE5 inhibitors, which act peripherally on the nitric oxide/cGMP pathway in erectile tissue and do nothing for desire.
The same receptor promiscuity that makes it work explains its most consistent unwanted effects. MC1R agonism on epidermal melanocytes raises cAMP, induces MITF and drives eumelanin synthesis, producing the focal hyperpigmentation seen with repeated dosing. Central MC4R signalling raises sympathetic outflow, which produces the transient rise in blood pressure and fall in heart rate documented in the label. Nausea, the commonest adverse effect by a wide margin, is also melanocortin-mediated via brainstem circuits.
What the research shows
The pivotal evidence is the RECONNECT programme: two identical 24-week randomised, double-blind, placebo-controlled phase 3 trials in premenopausal women with acquired, generalised hypoactive sexual desire disorder, using 1.75 mg subcutaneously as needed. Of 1,267 women randomised, 1,202 formed the modified intent-to-treat efficacy population; mean age was 39 years. Both co-primary endpoints were met, but the magnitude deserves stating plainly. The integrated placebo-adjusted improvement in the Female Sexual Function Index desire domain was 0.35 points on a scale running from 1.2 to 6.0, and the reduction in desire-related distress was 0.33 points on a 0-4 item. Notably, the number of satisfying sexual events did not increase significantly. The drug moved questionnaire scores for desire and distress; it did not reliably change how often participants had sex they enjoyed.
Tolerability drove a substantial dropout: roughly 18% of women on bremelanotide discontinued for adverse events versus about 2% on placebo. In the 52-week open-label extension, treatment-related nausea was reported by 40.4%, flushing by 20.6% and headache by 12.0%. That extension supported durability in those who stayed on treatment, but the attrition is the story as much as the durability: of 684 women who entered it, 272 completed. It is a self-selected group by construction.
The male evidence is worse than it looks. The most-cited male trial - a 2008 randomised comparison of intranasal bremelanotide in 342 men who had failed sildenafil - was published by an author whose work has since attracted at least fifteen retractions, and in January 2023 the Journal of Urology issued a formal Expression of Concern covering that paper along with thirteen others by the same group. It should not be treated as reliable evidence for anything. Separately and independently of that, the intranasal development programme in erectile dysfunction was halted in 2007 after blood pressure increases were observed, and no male indication has ever been pursued to approval. The honest summary is that bremelanotide is a real drug with a real evidence base in premenopausal women and a genuinely modest effect, and that it has essentially no trustworthy controlled evidence in men at all.
Evidence assessment
High-quality evidence
Two replicated, adequately powered phase 3 randomised controlled trials met their co-primary endpoints and led to FDA-approved labelling, though the effect sizes were small, the drug is approved in only one jurisdiction for one narrow indication, and the historical male erectile dysfunction citation is now under a formal Expression of Concern.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials High-quality evidence
Both co-primary endpoints were met - placebo-adjusted FSFI-desire improvement of 0.35 and FSDS-DAO item 13 reduction of 0.33 - but satisfying sexual events did not increase significantly and about 18% discontinued for adverse events.
Long-Term Safety and Efficacy of Bremelanotide for Hypoactive Sexual Desire Disorder Mixed evidence
Improvements were sustained over a year in women who continued treatment with no new safety signals; treatment-related nausea 40.4%, flushing 20.6%, headache 12.0%. Interpretation is limited by the heavy attrition and the self-selected nature of an open-label continuation cohort.
Responder Analyses from a Phase 2b Dose-Ranging Study of Bremelanotide Mixed evidence
Responder rates at the 1.75 mg dose reached statistical significance versus placebo across all seven endpoints examined in the modified intent-to-treat population, supporting selection of that dose for phase 3.
Salvage of sildenafil failures with bremelanotide: a randomized, double-blind, placebo controlled study Limited evidence
The paper reports a positive clinical response in 33.5% on bremelanotide versus 8.5% on placebo. BioRx does not regard this result as reliable - see note.
Safety
Nausea is very common (around 40%) and is the leading cause of discontinuation; vomiting, flushing, injection-site reactions, headache and fatigue are also frequent. The label records maximum increases of about 6 mmHg systolic and 3 mmHg diastolic blood pressure peaking 2 to 4 hours after dosing, with a corresponding fall in heart rate of up to 5 beats per minute, usually returning to baseline within 12 hours - which is why the label contraindicates use in uncontrolled hypertension or known cardiovascular disease and caps dosing frequency. Focal hyperpigmentation of the face, gums and breasts was reported in 1% of patients receiving up to eight doses per month, but in 38% of patients given the drug daily for eight days in a dedicated study, with a further 14% developing new pigmentary changes over eight more consecutive days; it may not fully resolve. It should not be used in pregnancy. The limits of the safety record matter: exposure data come almost entirely from premenopausal women using it intermittently for up to a year. There are no long-term data, no reliable data in men at the approved dose, and no safety characterisation whatsoever for the unregulated peptide sold online, where identity, purity and sterility are unverified.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No UK marketing authorisation. Bremelanotide has never been licensed by the MHRA for any indication and there is no approved European product. It is nevertheless widely sold online as an unlicensed 'research chemical' for sexual dysfunction; supply for human use in the UK on that basis is unlawful. |
| United States | FDA-approved 21 June 2019 (NDA 210557) as a subcutaneous autoinjector for acquired, generalised hypoactive sexual desire disorder in premenopausal women. Prescription-only, with labelled limits of one dose in 24 hours and no more than eight doses per month. Use in men, in postmenopausal women, or for erectile dysfunction is off-label and unstudied at the approved dose. Material sold online as 'PT-141' is not the approved product and is manufactured outside pharmaceutical regulation. |
| WADA (sport) | Not specifically named on the WADA Prohibited List. Melanocortin receptor agonists are not currently listed as a prohibited class, in or out of competition. |
Questions
Chemically the molecule is the same, but the products are not. The approved medicine is a regulated, sterile, dose-controlled autoinjector supplied on prescription with a label and a safety monitoring system behind it. 'PT-141' sold online is a research-grade powder from a supplier that has not been inspected for identity, purity or sterility, and is not authorised for human use. The pharmacology may be identical; the risk profile is not.
It beats placebo on validated questionnaire measures of sexual desire and desire-related distress, and the effect is statistically robust across two large trials. But the size of that effect is small - about 0.35 points on a desire scale spanning roughly five points - and the trials did not show a significant increase in satisfying sexual events. Roughly a fifth of women stopped taking it because of side effects, mostly nausea.
There is no approved use in men, and the controlled evidence is not merely thin but compromised. The trial most often cited - an intranasal study in 342 men who had failed sildenafil - is under a formal Expression of Concern issued by the Journal of Urology in 2023, and its lead author has more than a dozen retractions to his name. Independently of that, the intranasal male programme was halted in 2007 after blood pressure increases were observed. Any use in men today is off-label, unstudied at the currently approved dose, and unsupported by evidence anyone should rely on.
Bremelanotide is not selective for the MC4 receptor that mediates its effect on desire; it also activates MC1R on skin melanocytes, which is the receptor that drives eumelanin production. At the licensed frequency of up to eight doses a month, focal hyperpigmentation was reported in 1% of patients. In a study giving it daily for eight days, 38% developed it, most often on the face, gums and breasts, and it did not always resolve. That is the main reason the label caps dosing frequency.