Bremelanotide: the monograph

Bremelanotide is the peptide the gray market calls PT-141, and it is one of the few compounds in this fleet with a real FDA approval: Vyleesi, approved June 21, 2019, a subcutaneous autoinjector for acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women. The approval is genuine and the numbers behind it are modest, and this page gives both facts equal weight. In the two phase 3 trials, desire scores rose 0.5 and 0.6 points on a scale that runs from 1.2 to 6.0, versus 0.2 on placebo: a placebo-adjusted difference of 0.30 and 0.42 points. The number of satisfying sexual events did not significantly change. Both facts sit in the current label.

Three more label facts frame everything on this page. First, the boundary: Vyleesi is not indicated for postmenopausal women or men, and not indicated to enhance sexual performance; those words are the label's, not ours. Second, the tolerability trade: 40% of treated women reported nausea. Third, the market inversion: most 'PT-141' sold online is a compounded or research-grade vial aimed at men and at performance, which is exactly the population and purpose the label rules out, resting on early-phase trials from a program FDA says never led to an approved product.

Bremelanotide is a synthetic cyclic heptapeptide, Ac-Nle-cyclo-(Asp-His-D-Phe-Arg-Trp-Lys-OH), molecular weight 1025.2, an analog of the natural pigmentation hormone alpha-MSH. PT-141 is its original laboratory code from Palatin Technologies, which developed it and out-licensed North American rights to AMAG Pharmaceuticals for the approval; the application is now held by Cosette Pharmaceuticals. The lineage is unusually colorful: the family's sexual effects were discovered by accident during University of Arizona research on the tanning peptide Melanotan-II, when erections turned up as a side effect.

Development ran roughly 20 years and changed shape twice. Early trials, including the male erectile dysfunction program, used an intranasal spray; FDA's review records that the women's program moved to subcutaneous injection because systemic exposure through the nose was too variable. The approved product is therefore a fixed-dose 1.75 mg autoinjector, and no nasal or oral bremelanotide product has ever been approved.

Drugs@FDA lists exactly one bremelanotide product: Vyleesi (NDA 210557), a prescription 1.75 mg/0.3 mL single-dose autoinjector, approved June 21, 2019 as a new molecular entity. The indication is specific: premenopausal women with acquired, generalized HSDD, meaning low desire that developed after a period of normal desire, occurs regardless of partner or situation, causes marked distress, and is not explained by another condition, the relationship, or a medication. The label then draws the line in its Limitations of Use: not for HSDD in postmenopausal women, not for men, not to enhance sexual performance.

Everything sold as 'PT-141' outside that autoinjector, including every research-chemical vial and every compounded nasal spray, is unapproved by definition. FDA's own words about compounded drugs apply: they are not FDA-approved, and FDA does not verify their safety, effectiveness or quality before marketing. The earlier erectile dysfunction development programs, in FDA's summary, did not lead to approved products.

Bremelanotide is a melanocortin receptor agonist that activates several receptor subtypes nonselectively, with a potency order of MC1R, MC4R, MC3R, MC5R, MC2R; at therapeutic doses the label calls binding to MC1R and MC4R most relevant. MC4R is expressed on neurons across the central nervous system and sits at the center of appetite and autonomic regulation; MC1R is the melanocyte receptor that drives pigmentation. That receptor map explains this drug's signature effects better than any marketing page: MC4R activation plausibly links to the desire signal, and also to the transient blood pressure rise and nausea; MC1R explains why repeated dosing can darken skin. The label is blunt about the gap in the middle: the mechanism by which Vyleesi improves HSDD is unknown.

The animal work behind the desire claim is specific and worth stating precisely. In female rats, PT-141 selectively increased solicitation behaviors, the rat's appetitive courting repertoire, without changing lordosis or pacing, and a 2007 review localized the effect to the medial preoptic area. In male rats and nonhuman primates it produces erections, which is how the compound entered human testing in men. MC4R is also an appetite receptor: in two phase 1 trials in obese women, bremelanotide reduced caloric intake by about 400 kcal per day and weight by about a kilogram over about two weeks, a pharmacological signature shared with the melanocortin obesity drugs. A 2021 cryo-EM structure shows bremelanotide seated in MC4R alongside alpha-MSH, using the conserved peptide binding mode.

The approval rests on RECONNECT: two identical phase 3 randomized, double-blind, placebo-controlled trials (NCT02333071 and NCT02338960) that randomized 1,267 premenopausal women with acquired, generalized HSDD to as-needed bremelanotide 1.75 mg or placebo for a 24-week double-blind core, followed by a 52-week open-label extension. Most women used the drug two to three times per month; the median was 10 injections across the 24 weeks. The co-primary endpoints were a desire score (FSFI desire domain, range 1.2 to 6.0) and a distress score (FSDS-DAO item 13, range 0 to 4).

Both trials hit both co-primaries. Desire rose 0.5 and 0.6 points versus 0.2 on placebo (placebo-adjusted differences of 0.30 and 0.42; integrated 0.35); distress fell 0.7 versus 0.4 (differences of 0.37 and 0.29). The key secondary endpoint, the number of satisfying sexual events, did not significantly change in either trial (integrated P=.630), and under the trials' own statistical hierarchy that made the remaining secondary endpoints supportive and exploratory. The label prints the SSE tables; we reproduce the numbers rather than paraphrase them.

Context that honest reporting requires: premature discontinuation in the double-blind phase was substantially higher on drug than placebo (40% versus 13% in Study 1; 39% versus 25% in Study 2), driven largely by tolerability; the placebo response was high, around 35%, which the investigators note is typical for subjective sexual-function endpoints; and the 52-week extension was uncontrolled, so its larger cumulative changes (desire up 1.25 to 1.30 from core baseline) have no placebo comparison. The phase 2b dose-finding trial, where satisfying sexual events were the primary endpoint, did report a significant SSE gain of +0.7 versus +0.2 per month; that endpoint then failed in both larger, longer phase 3 trials.

Here is the honest arithmetic in one place. Desire: +0.35 points more than placebo (integrated), on a desire scale whose full width is 4.8 points (1.2 to 6.0). Distress: -0.33 points more than placebo on a 0-to-4 item. Satisfying sexual events: no significant change (means moved 0.0 versus -0.1 and 0.0 versus 0.0). The trials' own anchor-based responder threshold was a 1.2-point desire gain, which tells you the average treated woman did not reach the change the program itself defined as clinically meaningful; responder analyses (shown as figures in the label) exist because averages this size need them. None of this makes the approval fake. It makes the approval specific: a statistically real, modest average shift in how women score desire and distress, not a change in counted sexual events.

This is the question the gray market answers with confidence the record does not support. What exists: small, real, mostly 2004-to-2008 studies. Intranasal PT-141 produced RigiScan-verified erections in healthy men and Viagra-responsive ED patients at doses above 7 mg, onset around 30 minutes. Subcutaneous PT-141 produced erections above 1 mg in healthy men, and 4 to 6 mg worked in men with an inadequate sildenafil response. A 7.5 mg intranasal dose added to low-dose sildenafil beat sildenafil alone in 19 patients. The precursor Melanotan-II had already shown the effect in 1998: 8 of 10 men with psychogenic ED, rigid for 38 minutes versus 3 on placebo.

What that evidence is not: late-phase, replicated, or clean. The largest male trial, 342 sildenafil non-responders on 10 mg intranasal bremelanotide (33.5% versus 8.5% response), received an Expression of Concern from the Journal of Urology in 2023; the same author's randomized trial in women with arousal disorder was retracted outright. FDA's review states the earlier ED development programs did not lead to approved products, and records that the program abandoned the intranasal route for variable exposure while FDA's cardiovascular division was flagging blood pressure increases. The label's verdict on men is one sentence: Vyleesi is not indicated for men, and not to enhance sexual performance. A man buying a 'PT-141' vial today is dosing himself with phase 1 era evidence, two integrity-flagged trials, and no approved regimen at all.

Two different products share the name. Vyleesi is a prescription, fixed-dose 1.75 mg/0.3 mL sterile solution in a sealed single-use autoinjector, manufactured under an approved NDA. 'PT-141' vials are typically lyophilized peptide sold as a research chemical or compounded preparation: the buyer reconstitutes the powder, chooses a dose, and injects or sprays a product no regulator has verified. FDA's compounding page states the general rule plainly: compounded drugs are not FDA-approved, and FDA does not verify their safety, effectiveness or quality before marketing. This site does not publish reconstitution math for gray vials, deliberately: there is no approved vial format, so any mixing table would be an invented protocol for an unverified product.

The pharmacology adds one more caution the vendors never quote: bremelanotide exposure plateaus. Above roughly 7.5 mg subcutaneous, plasma Cmax stops rising with dose, so megadosing a vial mostly buys more time in the nausea, flushing and blood-pressure window rather than more drug at the receptor. And the known dose-response for harm is real: 38% of women developed focal skin darkening on daily dosing for just 8 days, versus 1% at the labeled at-most-8-per-month cadence.

The entire approved regimen is one sentence long: inject 1.75 mg subcutaneously in the abdomen or thigh, as needed, at least 45 minutes before anticipated sexual activity; never more than one dose in 24 hours; more than 8 doses per month is not recommended. The label is candid that the timing window is not fully characterized and the duration of effect after a dose is unknown; women in the trials settled at two to three uses per month. There is also a built-in exit: if symptoms have not improved after 8 weeks, the label says to stop.

Vyleesi comes as a prefilled, single-dose disposable autoinjector: no vial, no syringe drawing, no reconstitution, no dose selection. The user inspects the solution (clear, particle-free), injects into the abdomen or thigh, and discards the device. That design is not a convenience detail; it is the dose control. The fixed 1.75 mg device is what separates the approved product from every scale-and-syringe gray vial sold under the same molecule's name.

From the pooled placebo-controlled trials (Vyleesi versus placebo): nausea 40.0% versus 1.3%, flushing 20.3% versus 0.3%, injection site reactions 13.2% versus 8.4%, headache 11.3% versus 1.9%, vomiting 4.8% versus 0.2%, plus cough, fatigue, hot flush, paraesthesia, dizziness and nasal congestion each in the 2 to 3% range. Nausea starts at a median of one hour post-dose, lasts about two hours, hits 21% of women on the first dose and about 3% on later doses. A dedicated phase 4 study answered the obvious workaround: pre-dosing with 8 mg ondansetron did not reduce the nausea and is not recommended. Overall, 18% of women on drug discontinued for adverse reactions versus 2% on placebo; serious adverse reactions were 1.1% versus 0.5%, including a single open-label case of acute hepatitis whose relationship to the drug could not be excluded.

Bremelanotide's main interaction mechanism is mechanical: it slows gastric emptying, which can slow and reduce absorption of anything swallowed around the same time. The label singles out two consequences. Avoid Vyleesi while taking oral drugs that need threshold concentrations to work, such as antibiotics. And do not combine it with oral naltrexone taken for alcohol or opioid addiction, because bremelanotide can cut naltrexone exposure enough to cause treatment failure. In interaction studies, most tested oral drugs were unaffected to any clinically relevant degree; naltrexone and indomethacin were the exceptions.

Vyleesi is a drug to stop before pregnancy, not during it: the label tells women to use effective contraception and discontinue if pregnancy is suspected. The animal signal is taken seriously because no safe lower bound was found: fetal harm occurred in pregnant dogs at 16 times the human exposure and developmental delays in mouse offspring at 125 times, with no developmental no-effect level established in either species. Human data are thin: 7 pregnancies occurred across the trials with no major congenital anomalies reported, and a pregnancy exposure registry exists to collect more.

Store at or below 25 C (77 F); do not freeze; protect from light. Each autoinjector is single-dose and disposable: used once, discarded, never refilled. Discard the device if the solution is cloudy, discolored or contains particles.

Bremelanotide is fast in, fast out: after subcutaneous injection it peaks in about an hour (median Tmax 1.0 hour, range 0.5 to 1.0), with a terminal half-life of about 2.7 hours (range 1.9 to 4.0). Subcutaneous bioavailability is essentially complete at about 100%, protein binding is low at 21%, and the peptide is cleared by hydrolysis of its amide bonds, with 64.8% of a radiolabeled dose recovered in urine. Exposure rises less than proportionally with dose and the Cmax plateaus at 7.5 mg, about 4.3 times the approved dose. Renal and hepatic impairment raise exposure up to 2-fold (severe renal) and 1.7-fold (moderate hepatic). The 45-minute pre-activity timing in the label sits just before the plasma peak; the blood pressure effect peaks later, at 2 to 4 hours.

Checked absences, stated as such. No trial has tested bremelanotide against Addyi, the other approved HSDD drug; the comparison page on this site is therefore label-versus-label and meta-analysis-versus-trial, never head-to-head. The duration of effect after a dose is unknown; the label says so. Whether the desire benefit survives past 76 weeks is unmeasured, and the only long-term data (52-week extension) are uncontrolled, with 272 of 684 entrants completing. Long-term hyperpigmentation risk beyond the trial window is not characterized, and the label could not confirm resolution in all affected patients. Male efficacy at any marketed gray-market dose is untested in any modern randomized trial; the male program stopped at small 2004-to-2008 studies, two of which now carry integrity flags. Severe hepatic impairment pharmacokinetics were never studied. The mechanism for the desire effect itself is, in the label's own word, unknown.