PT-141 (Bremelanotide) - Melanocortin Peptide Guide
PT-141, also called bremelanotide, is a synthetic peptide that acts on melanocortin receptors in the central nervous system. Instead of working on blood flow the way PDE5 inhibitors do, it is a melanocortin receptor agonist that influences the brain pathways involved in sexual desire and arousal. The compound is the active ingredient of Vyleesi, the first melanocortin-based medicine approved by the FDA for acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women, and it also appears in the research-peptide market as a lyophilized vial. This reference guide summarises the published pharmacology, the approved dose, the pharmacokinetic data and the recorded side effects, and explains how PT-141 differs from Melanotan II.
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What PT-141 Is - A Melanocortin Receptor Agonist
PT-141 is a synthetic heptapeptide, a seven-amino-acid chain, and an analogue of alpha-melanocyte stimulating hormone (alpha-MSH). The scientific literature describes it as a deaminated derivative and a metabolite of Melanotan II (MT-II), which is the main reason the two compounds are so often discussed together. At the receptor level, bremelanotide is classified as a non-selective melanocortin receptor agonist: it binds and activates more than one melanocortin subtype, and its observed activity is attributed mainly to the MC3 and MC4 receptors.
The molecule circulates under three overlapping names, which adds to the confusion. PT-141 is the original research code used in the early studies on erectile function. Bremelanotide is the international nonproprietary name (INN). Vyleesi is the brand name of the FDA-approved injectable product. When a research catalogue lists a pt 141 peptide, the material is normally supplied as a lyophilized (freeze-dried) white powder in a sealed glass vial and is sold for laboratory investigation rather than for human use. A research-grade PT-141 (bremelanotide) vial belongs to that laboratory category only.
How PT-141 Works - MC4R Signaling in the Central Nervous System
Bremelanotide does not behave like a classic vasodilator. Sildenafil and tadalafil relax vascular smooth muscle through the nitric oxide pathway; PT-141 is instead a melanocortin-driven compound with a proposed central mode of action. By activating the melanocortin 4 receptor (MC4R) in the hypothalamus, the peptide is thought to modulate the brain circuits that regulate desire and arousal, including dopaminergic signalling.
A 2022 neuroimaging study in women with HSDD supports this central picture. The authors reported that MC4R agonism altered how sexual stimuli were processed in the brain, reducing self-consciousness and increasing sexual imagery. In clinical use the medicine is given before anticipated sexual activity, which points to a facilitating role on an existing arousal response rather than a spontaneous trigger. That distinction matters when comparing the peptide with drugs that act purely on blood flow.
PT-141 Pharmacokinetics - Half-Life, Tmax and Duration
After a single subcutaneous dose, bremelanotide is absorbed quickly and nearly completely. The FDA prescribing information for Vyleesi reports a mean terminal half-life of approximately 2.7 hours, with a range of 1.9 to 4.0 hours, and a time to peak plasma concentration of about one hour. An earlier pharmacology review of melanocortin peptides measured a serum half-life of roughly 120 minutes, which is consistent with the later label data.
Two practical points follow from those numbers. The plasma half-life is short, so the circulating compound is cleared within a few hours, yet the reported biological effects can outlast the plasma half-life because the receptor response lasts longer than the drug itself. The timing instruction in the label, to inject at least 45 minutes before anticipated activity, lines up with the roughly one-hour peak.
Route history also matters. Bremelanotide was first studied as an intranasal spray, but that formulation was discontinued during development after dose-related increases in blood pressure were observed. The programme was reformulated as a subcutaneous injection, which is the route used in the approved product and in the published pharmacokinetic data below.
| Parameter | Reported value |
|---|---|
| Route of administration | Subcutaneous injection (abdomen or thigh) |
| Absorption after injection | Close to complete |
| Time to peak (Tmax) | About 1 hour |
| Terminal half-life | About 2.7 hours (range 1.9 to 4.0 hours) |
| Serum half-life in early research | About 120 minutes |
| Timing before activity | At least 45 minutes |
| Blood pressure and heart rate change | Usually resolves within 12 hours |
| Maximum frequency | One dose per 24 hours, up to 8 doses per month |
PT-141 Subcutaneous Injection - Dosage Reference and Reconstitution
The approved dose of bremelanotide is 1.75 mg given by subcutaneous injection at least 45 minutes before anticipated sexual activity. The label limits use to no more than one dose in any 24-hour period and no more than eight doses in a month. This is the reference for the prescription Vyleesi autoinjector and is not a protocol for self-administered research peptides, which are not for human consumption.
The dose rests on the two Phase 3 RECONNECT trials, in which 1,247 premenopausal women with HSDD were randomised to bremelanotide 1.75 mg as needed or to placebo over 24 weeks. Both studies reported a statistically significant improvement in sexual desire and a reduction in the distress tied to low desire. Those are the data behind the approved dose, and they concern a regulated prescription product.
Research vials are distributed in lyophilized form and are reconstituted with a solvent before any laboratory handling. For a worked example, adding 2 mL of liquid to a 10 mg vial produces a 5 mg/mL solution; 1.75 mg of that is 0.35 mL, or 35 units on a U-100 insulin syringe. That arithmetic is shown only to illustrate how dilution and amount relate, not as a human dosing instruction. Reconstitution is done with bacteriostatic water, introduced against the glass wall instead of onto the powder, then mixed with a slow swirl, because shaking can shear the molecule.
PT-141 Side Effects - Nausea, Blood Pressure and Heart Rate
Across the Phase 3 programme the most frequent reactions were gastrointestinal and vascular. In the pooled trial data, nausea was reported by about 40 percent of participants assigned to bremelanotide versus 1.3 percent on placebo, facial flushing by roughly 20 percent, and headache by about 11 percent. Even with the high nausea rate, only 8.1 percent of participants discontinued the study drug because of it, and the symptom typically improves for most patients with the second dose.
- Nausea - the most common reaction, around 40 percent in Phase 3 trials, usually improving after the second dose
- Facial flushing - reported by roughly 20 percent of patients
- Headache - reported by about 11 percent
- Injection site reactions - about 13.2 percent, including pain, redness, bruising, itching and bleeding at the site
- Blood pressure and heart rate - a transient rise in blood pressure and a fall in heart rate occur after each dose and usually resolve within 12 hours
- Other reported reactions - vomiting, cough, fatigue, hot flush, tingling or numbness, dizziness and nasal congestion
The cardiovascular signal is the reason the label advises caution for people with uncontrolled high blood pressure or heart disease, and why the intranasal development path was abandoned. Any use of the approved medicine happens under a prescriber, and nothing in this article is medical advice.
PT-141 vs Melanotan II - What Sets Them Apart
PT-141 and Melanotan II are related molecules, and that relationship causes a great deal of confusion. Bremelanotide is described in the literature as a deaminated metabolite of MT-II, so the two share a melanocortin backbone. The difference lies in the research goal. Melanotan II was investigated as a tanning agent that acts on the melanocortin 1 receptor to drive melanin production, and its sexual effects were observed during that work. PT-141 was then developed from the same programme specifically for sexual function, with far less emphasis on the tanning response.
| Feature | PT-141 (bremelanotide) | Melanotan II |
|---|---|---|
| Origin | Deaminated metabolite and derivative of MT-II | Synthetic analogue of alpha-MSH |
| Main research focus | Sexual desire and arousal (MC4R) | Skin tanning (melanogenesis, MC1R) |
| Primary receptor emphasis | MC3 and MC4 | MC1 alongside MC3 and MC4 |
| Regulatory status | Approved prescription medicine for HSDD | Not approved as a medicine |
| Supplied as | Autoinjector; lyophilized research vial | Lyophilized research vial |
Both compounds are potent melanocortin agonists, but only bremelanotide has an approved medical identity and a published safety database, while Melanotan II has neither. Anyone comparing them should keep that in mind, and should also remember that raw peptides sold for research are a separate category from approved medicines. The wider peptide range in a research catalogue is listed for laboratory reference.