The PT-141 half-life is about 2.7 hours after a subcutaneous injection, meaning an injection under the skin. Half-life is how long it takes the amount in blood to fall by half. The label also reports that blood levels peak about an hour after the injection, so the half-life describes the decline after that peak: on average, about half of the peak level remains 2.7 hours later, and about a quarter after another 2.7 hours.
That does not mean the effect stops at 2.7 hours. It also does not mean the drug is completely gone after twice that time. The current Vyleesi label says the actual duration of effect is unknown.
What the PT-141 half-life really tells you
PT-141 and bremelanotide are two names for the same peptide. The label gives a mean terminal half-life of 2.7 hours, with a range of 1.9 to 4.0 hours. Terminal simply means the slower, final part of the body's clearing process.
A simple half-life calculation looks like this:
| Time after the peak (about 1 hour post-injection) | Estimated share of the peak level left in plasma* |
|---|---|
| 0 hours | 100% |
| 2.7 hours | 50% |
| 5.4 hours | 25% |
| 8.1 hours | 12.5% |
| 10.8 hours | 6.25% |
| 13.5 hours | About 3% |
*This uses the 2.7-hour average and starts the clock at the peak, not the injection, because the label reports a median time to peak of about one hour. Plasma is the liquid part of blood. It is a rough model, not a measurement from one person.
Five average half-lives add up to 13.5 hours after the peak, or roughly 14.5 hours after the injection. Using the full label range, five half-lives would span roughly 9.5 to 20 hours after the peak. That is a sensible answer to how long most of the drug may remain in blood. It does not establish a detection window, and it does not predict one person's response.
Peak level and felt effect are different clocks
The same label says bremelanotide reaches its median peak blood level at about one hour, with a range of 30 to 60 minutes. That is why the brand instructions use a lead time of at least 45 minutes before anticipated sexual activity. This is a label fact, not a dosing instruction for a compounded prescription.
The label also says the best timing window and the duration of effect have not been fully characterized. In other words, 45 minutes does not establish one exact onset, and 2.7 hours does not establish how long a response lasts. Blood level and felt response are different measurements, and people do not all clear or experience a medicine identically.
The two 2019 RECONNECT trials enrolled 1,267 premenopausal women with acquired, generalized hypoactive sexual desire disorder, meaning persistent low desire that causes distress and is not better explained by another condition. They studied subcutaneous bremelanotide as needed for 24 weeks, but they did not establish a precise effect window for every dose (Kingsberg et al., Obstetrics & Gynecology, 2019). For the brain pathway itself, see how PT-141 works.
Route and molecule both change the clock
Older bremelanotide studies used a nasal spray. One small randomized study gave a single 20 mg intranasal dose to 18 premenopausal women and collected response reports over the following 24 hours (Diamond et al., The Journal of Sexual Medicine, 2006). That 24-hour reporting period was not proof of a 24-hour effect. It also cannot supply a half-life for today's injected product.
The label notes that a 20 mg nasal dose produced about 2.5 times the peak blood level of the brand injection. Route, dose, and formulation all change exposure, so nasal and injection numbers are not interchangeable. The history is covered in why PT-141 nasal spray became an injection.
Kisspeptin sometimes appears in the same sexual-health conversation, but it works through reproductive-hormone signaling rather than bremelanotide's melanocortin pathway. Its clearance numbers cannot be borrowed for PT-141. What kisspeptin does explains that separate path.
Why the label still uses a 24-hour limit
The Vyleesi label sets a maximum of one dose within 24 hours and recommends no more than eight doses per month. Those are safety boundaries. They are not evidence that a single effect lasts a full day.
The label says doses closer together may add to blood-pressure effects. It also says more frequent use increases the time each month when blood pressure is raised and the risk of focal hyperpigmentation, meaning patches of darker skin. A randomized study of 397 premenopausal women found small, short-lived average blood-pressure increases after subcutaneous bremelanotide; the sharpest peaks usually lasted less than 15 minutes (White et al., Journal of Hypertension, 2017). The brand label reports that blood pressure and heart rate usually returned to baseline within 12 hours.
This is why the 24-hour rule should not be reverse-engineered into an effect claim. It is also why an individual schedule belongs to the prescriber and the pharmacy label. The separate PT-141 dosage guide covers how those decisions are made without turning trial figures into a home protocol.
A fresh warning about unlabeled seller vials
Through Promise, PT-141 is dispensed as a compounded medication, which is different from an FDA-approved product: the formulation offered here is not FDA-approved. A compounded medication is prepared by a licensed pharmacy for an individual patient from a prescription; it is not the brand autoinjector.
As of September 9, 2026, the day this article was written, the FDA had issued an August 24 warning letter to an online peptide seller whose website listed PT-141 alongside water intended to prepare injectable peptides. The agency said no approved application was in effect for that seller's PT-141 product and warned that injected products bypass some of the body's defenses against contamination.
The letter addressed that seller's products and claims. It was not a finding about every bremelanotide prescription. The useful contrast is accountability: a prescribed route has a named clinician, a dispensing pharmacy, a patient-specific label, lot records, and a path for reporting a problem. A licensed provider may still prescribe a compounded formulation; that decision is between the patient and the doctor.
What changes the estimate for one person
The 2.7-hour figure is an average, not a personal countdown. The brand label found higher overall exposure in people with kidney or liver impairment. Blood-pressure history, cardiovascular disease, pregnancy, and other medicines also matter. Bremelanotide can slow gastric emptying, meaning how quickly the stomach moves contents onward, which can change absorption of some oral medicines.
At Promise, a licensed provider reviews every request, and not everyone qualifies. If PT-141 is prescribed, the prescription and pharmacy label set the actual amount and timing; the 2.7-hour average is context for that plan, not a replacement for it.