PT-141

PT-141 is the deamidated metabolite of Melanotan II and binds MC1R, MC3R and MC4R, with the sexual effect attributed mainly to MC4R and MC3R in the hypothalamus. Activation there increases dopamine release in the medial preoptic area, which is the same node that mediates spontaneous sexual motivation. This is a completely different route from PDE5 inhibitors, which act peripherally on nitric oxide and cavernosal smooth muscle, which is why PT-141 can work in people for whom sildenafil does nothing and why it also works in women. Its affinity for MC1R is what produces the flushing and, with repeated use, the mild tanning some users notice.

Targets: MC4R, MC3R, MC1R, Hypothalamic dopaminergic pathways

• · This is the autoinjector dose studied in the RECONNECT phase 3 trials in premenopausal women with hypoactive sexual desire disorder.
• · Most people who go straight to 1.75 mg on a first dose get badly nauseated. Starting at 500 mcg and titrating up over several separate occasions is the single most useful harm-reduction step with this compound.
• · Nasal bioavailability is low and highly variable between formulations, so intranasal doses do not map cleanly onto injectable doses. Treat any nasal product as an unknown potency until you have tested it at the bottom of the range.

Work out your exact syringe units →

• very commonNausea— Around 40 percent in the phase 3 trials versus 1 percent on placebo. Dose-dependent and the main reason people quit.
• very commonFacial and upper-body flushing— MC1R-driven, usually starts within the first hour.
• commonHeadache— Often responds to hydration.
• commonInjection-site reaction— Transient redness or a small welt.
• commonTransient blood pressure rise and heart rate drop— Peaks around 2 to 4 hours after dosing; systolic rises of roughly 6 mmHg were seen in trials.
• uncommonVomiting— Mostly at higher doses or in first-time users who skipped titration.
• uncommonDarkening of gums, face or existing moles— Reported with repeated frequent dosing; more common with the parent compound Melanotan II.

• Uncontrolled hypertension - the transient pressor effect is real and measurable.
• Known cardiovascular disease, including recent myocardial infarction or unstable angina.
• Pregnancy - approved only for premenopausal women who are not pregnant, and contraception is advised.
• Concurrent naltrexone by mouth - bremelanotide significantly lowers naltrexone exposure and can undermine opioid or alcohol use disorder treatment.

• redundantmelanotan-2 — PT-141 is the metabolite of MT-II and hits the same receptors. Stacking them just stacks nausea and flushing.
• synergySildenafil or tadalafil — Different mechanisms - central desire versus peripheral vasodilation - and commonly combined. Note the effects on blood pressure run in opposite directions: PT-141 produces a transient pressor response (about +6/+3 mmHg, peaking 2 to 4 hours post-dose) while PDE5 inhibitors are vasodilators. The combination was implicated in the blood pressure signals that halted the intranasal bremelanotide ED programme, so separate first-time doses, and check blood pressure rather than assuming lightheadedness is the thing to watch for.
• conflictOral naltrexone — Bremelanotide reduces naltrexone absorption enough that the label warns against the combination.
• cautionAntihypertensive medication — The pressor effect can blunt blood pressure control for several hours.

• · Check resting blood pressure before you start if you have any cardiovascular history.
• · Note the interval between injection and effect on your first few doses so you can time it properly rather than redosing.
• · Photograph moles before regular use if you plan to dose frequently, since pigment changes complicate later melanoma surveillance.

Approved in the US as Vyleesi for premenopausal HSDD and available by prescription. Everything sold as PT-141 in vials online is unapproved research chemical, and it is not approved for men anywhere.

• Vyleesi (bremelanotide) FDA prescribing information (label)
• Kingsberg et al. 2019, RECONNECT phase 3 trials of bremelanotide for HSDD, Obstetrics & Gynecology (trial)
• Molinoff et al. 2003, PT-141 melanocortin agonist for the treatment of sexual dysfunction, Annals NY Academy of Sciences (review)

MC4R and MC3R are Gs-coupled, so agonism raises adenylyl cyclase activity and intracellular cyclic AMP, activates protein kinase A, and shifts CREB-dependent transcription in the neurons carrying the signal. The neurons that matter sit in the medial preoptic area and the paraventricular nucleus of the hypothalamus. Activation there drives oxytocinergic projections down to the spinal autonomic centres controlling the cavernosal vascular bed, and increases dopamine release in the medial preoptic area, which is the node that generates sexual motivation rather than sexual mechanics. That two-arm output is why the drug produces both wanting and erection, and why it still works when the peripheral nitric oxide pathway that sildenafil amplifies is already broken. It also explains the side effect profile exactly. MC4R is densely expressed in the area postrema and nucleus tractus solitarius, which is the brainstem vomiting centre, so nausea is not an impurity problem or a bad batch - it is the same receptor doing its other job. MC1R on cutaneous vasculature and mast cells produces the flushing. Central melanocortin tone raises sympathetic outflow, which is where the transient 6 mmHg systolic rise comes from. The most useful clinical fact in all of this is the mismatch between the plasma curve and the subjective effect: plasma is essentially gone by twelve hours on a 2.7 hour half-life, but users routinely report eight to twenty-four hours of effect, because what the drug does is engage a neural circuit rather than occupy a receptor continuously. Chasing a fading feeling with a second dose is therefore the classic beginner error, and it buys nothing but nausea.

The dominant failure is a first dose of 1.75 mg taken 45 minutes before a date. You spend the evening pale and nauseated, conclude the compound is rubbish, and never touch it again. Titration fixes this almost entirely. The second failure is redosing: plasma falls faster than the effect does, so people take a second shot four hours in, feel nothing extra except more nausea, and end up with a pressor effect stacked on itself. The third is intranasal potency roulette, because grey-market nasal formulations vary enormously and are not interchangeable with injectable doses. The fourth is people with genuinely low testosterone or a raised prolactin using PT-141 as a substitute for finding out why their libido is gone - melanocortin agonism does not fix hypogonadism. Finally, dosing well above the eight-per-month label ceiling is where the pigment effects start, and darkened gums, freckles and moles matter mainly because they wreck your ability to spot a changing mole later.

1. 500 mcgFirst dose — Take this on a day when you have nothing planned. The purpose of dose one is to find out how nauseated you get, not to have sex.
2. 750 mcgSecond occasion, at least 48 hours later — Only step up if the nausea at 500 mcg was mild and short. If it was not, stay at 500.
3. 1 mgThird occasion — Where most men who use it off-label settle. A useful number of people never need more than this.
4. 1.75 mgFourth occasion and beyond — The approved Vyleesi dose. Going straight here on dose one is the single most common reason people conclude PT-141 does not work for them - they were too sick to notice whether it did.

• MC4R — Low nanomolar in published binding work, though I did not resolve a specific Ki from a primary source here.

  The principal target for desire and erection. Gs-coupled, raises cyclic AMP in medial preoptic and paraventricular hypothalamic neurons, and drives both the dopaminergic motivation arm and the oxytocinergic pro-erectile arm. Also the receptor responsible for the nausea and the appetite suppression.

• MC3R

  Contributes to the central sexual effect and to energy-balance signalling. Hard to separate from MC4R in humans because no selective ligand has been through clinical work.

• MC1R

  Vascular and melanocyte receptor. Responsible for the flushing, and for the mild tanning and gum or mole darkening that shows up in people who dose far more often than the label allows.

• MC5R

  Exocrine and sebaceous gland receptor. Probably behind occasional reports of oilier skin, though that is inference rather than something demonstrated.

• RECONNECT Study 301 (NCT02333071) 3 · 24 weeks · 2019

  Co-primary endpoints of change in Female Sexual Function Index desire domain score and change in the Female Sexual Distress Scale desire/arousal/orgasm item 13 distress score, in premenopausal women with acquired generalised hypoactive sexual desire disorder. Both were met against placebo.

• RECONNECT Study 302 (NCT02338960) 3 · 24 weeks · 2019

  Identical design and identical co-primary endpoints to Study 301, both met. The two trials together enrolled 1247 premenopausal women and were followed by a 52-week open-label extension.

• Open-label extension of the RECONNECT trials 3 extension · 52 weeks · 2019

  Long-term safety and tolerability over a year of as-needed use. Nausea remained the dominant adverse event and the dominant reason for discontinuation, and no new safety signal emerged.

• Intranasal PT-141 double-blind placebo-controlled safety, pharmacokinetic and pharmacodynamic study in men 1/2 · 2004

  Safety, pharmacokinetics and erectile response by RigiScan in healthy men and men with mild to moderate erectile dysfunction. Showed dose-dependent erectile activity by a route later abandoned over blood pressure.

Injection to peak plasma is about an hour. Flushing and any nausea usually announce themselves between 30 and 90 minutes. Subjective desire and spontaneous arousal generally arrive between 45 minutes and two hours, which is why the label says dose at least 45 minutes ahead. The effect then plateaus and persists well beyond the plasma curve - most people describe a useful window of six to twelve hours, and some report residual responsiveness into the next day. Blood pressure peaks two to four hours in and is back to baseline within twelve. There is no loading period and no cumulative build-up: dose one behaves like dose fifty, other than the nausea attenuating slightly with repeated exposure.

The common pairing is PT-141 plus a PDE5 inhibitor, and mechanistically it makes sense - central desire from one, peripheral vasodilation from the other. What nobody thinks about is that their blood pressure effects run in opposite directions and peak at different times, so run each alone at least once before combining, and take an actual reading rather than relying on whether you feel dizzy. Stacking PT-141 with Melanotan II is pointless, since PT-141 is MT-II's metabolite: you are dosing the same pharmacology twice and doubling the nausea. Stacking with kisspeptin-10 is popular and has no data behind it at all; the mechanisms are genuinely independent so it is not absurd, but you should know you are the experiment. Oral naltrexone is the one hard conflict - bremelanotide meaningfully lowers naltrexone exposure, which matters enormously if that naltrexone is holding an alcohol or opioid problem in check.

Against sildenafil and tadalafil, PT-141 is not a competitor but a different axis - PDE5 inhibitors amplify an erection you are already trying to have, PT-141 makes you want to have one. That is why it works in men who are non-responders to PDE5 drugs and why it works at all in women. Against flibanserin, the other approved HSDD drug, PT-141 is on-demand rather than daily, does not require alcohol abstinence and does not need weeks of build-up, but it costs more per act and it makes a substantial minority of people nauseated. Against Melanotan II, PT-141 is the same molecule minus the C-terminal amide, and that one change strips most of the MC1R-driven tanning while keeping the sexual effect, which is exactly what it was engineered to do. If you want the sexual effect, PT-141 is the cleaner tool. If you want the tan, it is the wrong tool.

$15–$60/month. Research-chemical 10 mg vials typically run 40 to 90 dollars, and at 1 mg per use twice a week one vial covers more than a month. Vyleesi is in a different universe - US list pricing for a four-autoinjector carton has run from the high hundreds to over a thousand dollars, so roughly 800 to 1200 dollars a month at label dosing. Treat both figures as indicative; grey-market pricing moves constantly and US list prices are not what anyone actually pays.

• ?Published receptor binding affinities for bremelanotide at MC1R, MC3R, MC4R and MC5R exist in the medicinal chemistry literature, but I did not resolve specific Ki values from a primary source in this session, so the affinity fields are descriptive rather than numeric.
• ?Blood-brain barrier penetration is marked partial by inference. The drug plainly acts on hypothalamic circuitry in humans, but I could not find a quantified human CSF-to-plasma ratio, and some of the central effect may be mediated at circumventricular organs where the barrier is naturally leaky rather than by true parenchymal penetration.
• ?Steady state and accumulation are listed as not applicable because the label found no additive blood pressure or heart rate effect over sixteen days of daily dosing. Whether tolerance to the desire effect develops with sustained frequent use is genuinely unknown, since nobody has studied dosing above the eight-per-month cap.
• ?The male off-label subcutaneous ladder given here is extrapolated from the female label plus community practice. The phase 2 male data used the intranasal route at different doses, so no male trial validates 500 to 1750 mcg subcutaneously.
• ?Cost figures are indicative and were not verified in this session.

• Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials Kingsberg SA, Clayton AH, Portman D, Williams LA, Krop J, Jordan R, Lucas J, Simon JA, Obstetrics and Gynecology, 2019 · PMID 31599840

  The RECONNECT phase 3 trials, and the evidence the approval rests on. Worth reading for the effect size as much as the p value: the desire improvement is real but modest.

• Long-Term Safety and Efficacy of Bremelanotide for Hypoactive Sexual Desire Disorder Simon JA, Kingsberg SA, Portman D, Williams LA, Krop J, Jordan R, Lucas J, Clayton AH, Obstetrics and Gynecology, 2019 · PMID 31599847

  The 52-week open-label extension. The useful number in here is how many people stopped because of nausea rather than because it stopped working.

• PT-141: a melanocortin agonist for the treatment of sexual dysfunction Molinoff PB, Shadiack AM, Earle D, Diamond LE, Quon CY, Annals of the New York Academy of Sciences, 2003 · PMID 12851303

  The original pharmacology paper describing PT-141 as a melanocortin agonist for sexual dysfunction, from the group that developed it.

• Double-blind, placebo-controlled evaluation of the safety, pharmacokinetic properties and pharmacodynamic effects of intranasal PT-141, a melanocortin receptor agonist, in healthy males and patients with mild-to-moderate erectile dysfunction Diamond LE, Earle DC, Rosen RC, Willett MS, Molinoff PB, International Journal of Impotence Research, 2004 · PMID 14963471

  The male erectile dysfunction data, by the intranasal route. This is the closest thing to trial evidence behind the way men actually use PT-141, and it is phase 1/2, not phase 3.

• VYLEESI (bremelanotide) injection - FDA prescribing information DailyMed / FDA, 2019

  Section 12.3 is the source for every pharmacokinetic number on this page: tmax, 25 L volume of distribution, 6.5 L/hr clearance, 21 percent protein binding, and the 64.8 percent urinary recovery.