Section V — The Numbers
PT-141 Dosage, Pharmacokinetics, and Routes in the Record
The approved label figures and the studied research doses, set out as what was administered and measured — never as a regimen for any reader to follow.
Before the figures
This page reports PT-141 dosage as it appears in the trials and the prescribing information, and nothing more. The approved figure is plain to state: 1.75 mg injected just under the skin, taken only when needed, with strict monthly limits. Earlier studies used other amounts and other routes. All of it is recorded here as a finding — what researchers gave, by which route, with what result — and none of it is a recommendation, a protocol, or advice. This site recommends no dose for anyone.
The approved dose
In the approved use, the studied bremelanotide dose is 1.75 mg subcutaneously, as needed, taken at least 45 minutes before anticipated sexual activity, with no more than one dose per 24 hours and no more than 8 doses per month [11]. The product is a prefilled subcutaneous autoinjector, not a powder to be reconstituted [11].
These limits are part of the approval, not optional refinements: the once-per-24-hours and eight-per-month ceilings are written into the prescribing information, in part because frequency drives both the tolerability burden and the pigment effect [11]. Reported here as a label parameter, this is not guidance to self-administer [11].
The research dose history
Before the approved figure settled, the dose record ranged more widely. Phase 2 subcutaneous dose-finding in women tested 0.75, 1.25, and 1.75 mg, which is how 1.75 mg was selected as the dose carried into the pivotal trials [3] [11]. Early intranasal research in men with erectile dysfunction escalated to roughly 7-20 mg, with a statistically significant erectile response reported above about 7 mg — a far higher figure than the approved subcutaneous dose, reflecting the lower, more variable absorption of the nasal route [1].
A separate Phase 1 obesity protocol gave subcutaneous doses up to 2.5 mg, up to three times daily for 15 days — a high-frequency research regimen, not a therapeutic schedule, used to probe the appetite effect of MC4R [11]. Each of these is a study parameter from a specific protocol; none describes how the approved medicine is used, and the spread itself is a caution: the same molecule was administered very differently across indications and routes, so a number lifted out of one study says nothing about another [1] [3] [11].
How is PT-141 administered and prepared in studies?
In the approved use, administration is straightforward by design: a subcutaneous injection from a prefilled autoinjector, taken as needed at least 45 minutes before anticipated sexual activity [11]. There is no powder to reconstitute and no mixing step — the autoinjector delivers a fixed 1.75 mg dose, which is part of why the label can hold frequency to a strict ceiling [11].
This matters for how the record should be read. The approved product is a finished, fixed-dose device, whereas material sold as 'PT-141 research chemical' is unregulated laboratory powder of uncertain identity, purity, and concentration [11]. The two are not interchangeable, and the documented dose-response and safety figures — established for the finished medicine — cannot be assumed to carry over to unregulated material. This site describes preparation and administration as studied, not as a procedure for anyone to perform [11].
What is the half-life of PT-141?
By the prescribing information, the PT-141 half-life is approximately 2.7 hours (range 1.9-4.0 h) terminal, after subcutaneous administration, with a median time to peak (Tmax) of about 0.5-1.0 hour [11]. Early intranasal studies reported a shorter half-life of about 1.85-2.09 hours [11]. The drug is a short-acting agent in the bloodstream — present in meaningful amounts for hours, not days [11].
How long does PT-141 last in practice?
There are two clocks, and they disagree. The pharmacokinetic clock is short: a terminal half-life around 2.7 hours means the drug clears within hours of a subcutaneous dose [11]. The effect clock runs longer: in the mechanistic fMRI study, MC4R agonism raised sexual desire for up to 24 hours after a single dose [5].
That gap — a desire window measured in a day against a half-life measured in hours — is itself mechanistic evidence. It is consistent with a central action that shifts circuit state, rather than a peripheral effect that tracks the moment-to-moment blood level of the drug [5] [11].
The full pharmacokinetic profile
The remaining pharmacokinetics are documented in the label. Volume of distribution is about 25.0 L; clearance about 6.5 L/hr; serum protein binding about 21% [11]. The compound is metabolised by hydrolysis of the cyclic-peptide amide bonds and ordinary peptidase digestion, and excreted 64.8% renally and 22.8% in faeces from a radiolabeled dose [11].
The cyclic lactam structure is the throughline: it confers greater stability than the linear melanocortin peptides, which is what makes a subcutaneous, as-needed peptide drug feasible at all [1] [11]. The routes studied were subcutaneous (the approved route), intranasal (early development, discontinued for pharmacokinetic variability), and intravenous (early pharmacology) [11].