PT-141 Dosage Guide: Vyleesi FDA Label, Units and cc Conversion & Reconstitution

PT-141 at a glance

What it is

Bremelanotide, a synthetic cyclic seven-residue melanocortin peptide, developed from the alpha-MSH analogue melanotan II. Known in research settings as PT-141; the approved product is Vyleesi.

Approval status

FDA-approved in 2019 as Vyleesi (bremelanotide injection) for acquired, generalised hypoactive sexual desire disorder in premenopausal women. Supplied as a 1.75 mg / 0.3 mL single-dose autoinjector; the current label is held by Cosette Pharmaceuticals and was last updated in November 2025.

Mechanism, per the label

A melanocortin receptor agonist that nonselectively activates several receptor subtypes, binding principally at MC1R and MC4R. The label states plainly that the mechanism by which it improves the approved condition is unknown.

Approved dose

1.75 mg subcutaneously into the abdomen or thigh, as needed, at least 45 minutes before anticipated sexual activity. No more than one dose in 24 hours, and no more than eight doses per month.

Half-life

Approximately 2.7 hours, with a reported range of 1.9 to 4.0 hours. Tmax is about 1 hour. These are measured label values, not estimates.

Bioavailability

About 100% by the subcutaneous route - unusually high, and one of the few peptides where the label states it outright. Plasma protein binding 21%, volume of distribution 25.0 +/- 5.8 L.

Most common adverse reaction

Nausea, in 40.0% of patients on drug against 1.3% on placebo - a 30-fold difference and by a wide margin the dominant tolerability issue.

The dosing-frequency finding

Focal hyperpigmentation occurred in 1% of patients taking up to eight doses per month, but in 38% of patients dosed daily for eight days. Frequency, not dose size, is what drove it - which matters because research-market use often ignores the monthly cap.

Contraindications, per the label

Uncontrolled hypertension or known cardiovascular disease. Bremelanotide transiently raises blood pressure in everyone who takes it.

Research-market status

PT-141 sold as a lyophilised research vial is not the approved product, is not approved for use in any person in that form, and is supplied for research and educational use only.

Reported ranges from research/community — examples, not recommendations.

What it is / mechanism

Bremelanotide is a cyclic seven-residue peptide that acts on the melanocortin receptor family, and its origin explains most of its behaviour. It descends from melanotan II, a synthetic analogue of alpha-melanocyte-stimulating hormone that was developed for tanning; bremelanotide is a metabolite of that compound, refined into its own drug. Understanding that lineage explains both what it does and its most distinctive side effect, because the melanocortin family is where pigmentation and central arousal signalling happen to sit next to each other. The label describes it as a melanocortin receptor agonist that nonselectively activates several receptor subtypes, with binding principally at MC1R and MC4R. That nonselectivity is the whole story. MC4R is expressed in the central nervous system and is the receptor thought to be relevant to the approved indication; MC1R sits on melanocytes and governs melanin production. A drug that agonises both will act centrally and, given enough exposure, will also darken skin - not as an unrelated toxicity but as an on-target effect at the wrong receptor. What the label conspicuously does not do is claim to know how the drug works for its indication. It states that the mechanism by which bremelanotide improves hypoactive sexual desire disorder is unknown. That is a striking sentence to find in an approved label, and it is worth quoting accurately, because research-market pages routinely present a confident central-pathway mechanism that the regulator's own document declines to assert. What is established is the receptor pharmacology; what is inferred is the route from receptor to effect. The route of administration matters mechanistically too. Bremelanotide is given subcutaneously and its subcutaneous bioavailability is approximately 100% - the label's own figure. Essentially all of an injected dose reaches circulation, which is unusual and makes the relationship between injected amount and systemic exposure unusually direct. There is no first-pass loss to absorb variability, so an error in measuring a dose translates proportionally into an error in exposure. Metabolism is by multiple hydrolyses of the amide bonds in the cyclic peptide, and elimination is split between routes: in the mass-balance study, 64.8% of total radioactivity was recovered in urine and 22.8% in faeces. Distribution is modest, with a volume of distribution of 25.0 +/- 5.8 L and plasma protein binding of 21%, so the drug is not extensively tissue-sequestered or heavily bound. Combined with a half-life of roughly 2.7 hours, this is a compound that arrives quickly, does not linger, and does not accumulate on the approved intermittent schedule - which is precisely why the schedule is intermittent.

Researched effects

The approved effect claim is narrow and specific: Vyleesi is indicated for acquired, generalised hypoactive sexual desire disorder in premenopausal women, defined in the label as low sexual desire causing marked distress or interpersonal difficulty and not accounted for by a co-existing medical or psychiatric condition, relationship problems, or the effects of a medication or drug substance. Each of those exclusions is part of the indication, not fine print - the approved population is defined as much by what has been ruled out as by what is present. Several things about the approved use are routinely lost in translation to the research market. The drug is used episodically, on demand, at least 45 minutes before anticipated activity - it is not a daily or continuous therapy. It is approved only in premenopausal women; the label's indication does not extend to men or to postmenopausal women, whatever the research-market usage pattern suggests. And the approval is for a desire disorder, which is a different clinical target from erectile function, though the two are habitually conflated in commercial copy about PT-141. The tolerability profile is a large part of the honest picture, because it is unusually prominent for an on-demand product. In the controlled trials, nausea occurred in 40.0% of patients receiving bremelanotide against 1.3% on placebo. Flushing occurred in 20.3% against 0.3%. Headache occurred in 11.3% against 1.9%, injection-site reactions in 13.2% against 8.4%, and vomiting in 4.8% against 0.2%. Two of those - nausea and flushing - separate from placebo by more than an order of magnitude, so they are attributable effects rather than background noise. The label notes that nausea improves for most patients with the second dose, which is a genuinely useful piece of information and one of the few reassuring details in the table. The blood-pressure effect is best understood as a predictable pharmacological action rather than an adverse event that happens to some people. Bremelanotide produces transient increases in blood pressure after every dose, with maximal mean rises of about 6 mmHg systolic and 3 mmHg diastolic, peaking 2 to 4 hours after dosing and generally resolving within 12 hours. Those mean increases are modest, and in a healthy person they are unremarkable; the label nonetheless contraindicates the drug in uncontrolled hypertension or known cardiovascular disease, because a reliable pressor effect in someone whose cardiovascular reserve is already compromised is a different proposition from the same effect in someone whose is not. What is reported in research-community settings - use by men, use for erectile response, use at frequencies far above the approved cap - has no controlled data behind it in the form the market uses. It is not supported by the approved label, which covers a different population and a different endpoint. Nothing on this page is a claim that PT-141 treats, prevents or improves any condition, and nothing here is medical advice.

Dosage — reported ranges (overview)

PT-141 belongs to the small group of research-market peptides where a real approved human dose exists, and comparing it with what the market does is unusually instructive. The approved dose is 1.75 mg subcutaneously, into the abdomen or thigh, taken as needed at least 45 minutes before anticipated sexual activity. Two limits accompany it: no more than one dose in any 24-hour period, and no more than eight doses in a month. The 45-minute interval is not arbitrary - it lines up with a Tmax of about one hour, so the instruction is essentially telling the patient to dose so that activity coincides with peak concentration. The research community commonly reports figures in the range of roughly 0.5 to 2 mg, which straddles the approved 1.75 mg and is, unusually, in the same neighbourhood rather than wildly above it. The gap between approved and reported practice on this compound is therefore not mainly about dose size. It is about frequency, and about population. The frequency point is where the label has something concrete and under-reported to say. Focal hyperpigmentation was seen in about 1% of patients taking up to eight doses per month - the approved maximum - and in 38% of patients dosed daily for eight days. That is a shift from roughly one in a hundred to well over one in three, and the variable that changed was not the size of the dose but how often it was given. Anyone using this compound more frequently than the approved cap is operating in the exposure region where the label documents a materially different pigmentation risk, and the effect is reported to be more pronounced in people with darker skin. This is the single most practically useful thing the label offers a research-market reader, and it is almost never quoted. The population point is simpler: the approved indication covers premenopausal women, and the trials that generated both the efficacy and the adverse-reaction figures were conducted in that population. Reported use extends well beyond it. When a man uses this compound at 1.75 mg, he is using a dose established in a different population for a different endpoint, and neither the efficacy data nor the 40% nausea figure was generated in people like him. That cuts in both directions - the tolerability data may not transfer either - but it means the label's numbers should be read as a reference point rather than as a validated protocol for how the compound is actually being used. The formulation difference also makes the approved figure less portable than it looks. Vyleesi is a manufactured, quality-controlled solution at 1.75 mg in 0.3 mL, roughly 5.83 mg/mL, delivered by a fixed-dose autoinjector that removes measurement error entirely. Research-market PT-141 is a lyophilised powder of unverified content that the buyer reconstitutes and measures by eye against syringe graduations. The number 1.75 mg means something different in those two settings, and with a compound whose subcutaneous bioavailability is about 100%, a measurement error translates almost fully into an exposure error. Everything above describes an approved regimen and what is reported, for educational purposes. It is not a recommendation, and PT-141 purchased as a research chemical is not the approved product and is not approved for use in any person.

A printable protocol sheet with a reconstitution reference and an injection log comes with All-Access Lifetime.

Reconstitution — bac-water math

The approved product needs no reconstitution: Vyleesi is supplied as a ready-to-use solution, 1.75 mg in 0.3 mL - approximately 5.83 mg/mL - in a single-dose autoinjector. Research-market PT-141 is the opposite: a lyophilised powder, commonly in 10 mg vials, that has to be reconstituted with bacteriostatic water before anything can be drawn. The arithmetic below applies to that research format. Concentration in mg per mL is the vial's milligram content divided by the millilitres of bacteriostatic water added; syringe units are (target mg / concentration) x 100, because a 1 mL U-100 insulin syringe is graduated into 100 units across one millilitre. Because this compound is frequently discussed in cc rather than units, it is worth fixing the conversion once: 1 cc equals 1 mL equals 100 units, so 0.5 cc is 50 units and 0.1 cc is 10 units - cc and mL are the same volume, and units are hundredths of it. The table works a 10 mg vial at four volumes against a 1 mg example and the approved 1.75 mg figure, so the approved dose can be read directly in syringe units at each concentration. These are arithmetic examples, not recommendations. Note that all four preparations keep both figures inside a single 1 mL syringe, which is not true of every peptide. The calculator on this page runs the same computation for any vial size and volume.

This is concentration math, not a dose recommendation.

Injection / administration basics

The approved route is subcutaneous, into the abdomen or thigh, using a fixed-dose autoinjector - the label specifies both sites explicitly. Research-market material is reconstituted and drawn manually into an insulin syringe instead, which introduces a measurement step the approved product does not have. General handling concepts such as aseptic technique, site rotation and timing relative to onset are covered here as general educational information; the detailed workflow comes with All-Access Lifetime, which includes the printable protocol sheet and injection log for every compound. Nothing here is a personal administration protocol or an instruction to administer anything to a person.

Half-life & frequency rationale

PT-141 has a properly measured human half-life, which distinguishes it from most compounds in this market: approximately 2.7 hours, with a reported range of 1.9 to 4.0 hours. Tmax is about 1 hour, with a range of 0.5 to 1.0 hours. Both figures come from the approved label rather than from inference or animal scaling. Those two numbers explain the approved dosing instruction better than any narrative could. Being told to inject at least 45 minutes before anticipated activity is simply an instruction to let the compound reach peak concentration, which happens at around an hour. A 2.7-hour half-life then means the great majority of a dose has cleared within a working day - after four half-lives, roughly eleven hours, only a few per cent remains. That short exposure window is why the approved product is an on-demand treatment rather than a daily one, and why no accumulation is expected on the approved schedule. It also frames why dosing frequency, not dose size, is the axis the label warns about. Because clearance is quick, taking the compound daily does not produce dramatic accumulation of drug in plasma - yet daily dosing for eight days still produced focal hyperpigmentation in 38% of patients against 1% at the approved monthly cap. The pigmentation effect tracks repeated receptor stimulation over time rather than a high peak concentration, which is exactly the pattern one would expect from an MC1R-mediated effect on melanocytes. A short half-life is not, on its own, protection against the consequences of frequent use.

Stacking — overview

PT-141 is discussed in far fewer combinations than the repair peptides, and the combinations that do circulate are generally paired with oxytocin on a loosely central-signalling rationale. There is no controlled human data on any such combination, and the pairing rationale is speculative rather than evidence-based. Two specific cautions are worth stating: the compound's blood-pressure effect is a documented, reliable pharmacological action, so combining it with anything else that affects vascular tone is a genuine interaction question rather than a theoretical one, and the label's contraindication in cardiovascular disease applies regardless of what else is in a protocol. Mechanism-level detail on the reported combinations and their specific cautions is covered in the paid PT-141 Stacking Module included with this guide.

For how combinations are grouped by research context, the named blends, and why a pre-mixed blend vial cannot be calculated from its total milligrams, see the peptide stacks guide.

Storage & handling

• Approved product, for reference: store at or below 25 degrees Celsius, do not freeze, protect from light - the label's own instruction for the ready-to-use autoinjector.
• Research-market lyophilised powder, unopened: store cold; the dry form is the stable one and tolerates shipping without refrigeration for short periods.
• Reconstituted with bacteriostatic water: refrigerate at roughly 2-8 degrees Celsius and protect from light. Commonly reported usable windows of several weeks are handling conventions, not stability data measured for this peptide in this format.
• Avoid repeated freeze-thaw cycles; direct the diluent down the vial wall rather than shaking, and wipe the stopper with alcohol before each entry.

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