PT-141

PT-141, now known by its generic name bremelanotide, is a small ring-shaped (cyclic) peptide of seven amino acids. It is a synthetic analogue of alpha-melanocyte-stimulating hormone and activates two melanocortin receptors in the brain, MC3R and MC4R (Diamond 2006). It does not act on blood flow to the genitals in the way that drugs such as sildenafil do; its proposed effect is on desire, through the brain.

It was developed by the US company Palatin Technologies. The first human studies, in the early 2000s, tested it as a nasal spray and as an injection in men with erectile dysfunction (Diamond 2004; Rosen 2004). Development then moved to women: a small laboratory study, a phase 2b dose-finding trial with an under-the-skin injection (Clayton 2016), and two phase 3 trials known as RECONNECT (Kingsberg 2019). On 21 June 2019 the FDA approved it as Vyleesi, an autoinjector, for premenopausal women with acquired, generalised hypoactive sexual desire disorder (HSDD).

Almost every clinical study was designed, funded or co-authored by the companies developing the drug (Palatin and, later, AMAG Pharmaceuticals). An independent re-analysis of the phase 3 data agreed on the size of the benefit but argued that it is small and that dropouts due to side effects were underreported (Spielmans 2021).

• Type: synthetic cyclic peptide, 7 amino acids; melanocortin receptor agonist.
• Studied for: low sexual desire in premenopausal women; earlier, erectile dysfunction in men.
• Strongest evidence: two phase 3 randomised placebo-controlled trials in 1,267 women, plus a 52-week open-label extension.
• Legal status: FDA-approved as Vyleesi for one indication in women. Not approved for men or for any other use.

Sources: Vyleesi label (Cosette Pharmaceuticals). Checked on Oct 26, 2026.

At a glance: 8 studies report a dose (7 in people, 1 in animals).

Doses used in human studies

• Kingsberg SA 2019: 1.75 mg as needed before anticipated sexual activity (Subcutaneous autoinjector, as needed; 24 weeks)
• Diamond LE 2004: Range of single intranasal doses; erectile responses were significant at doses above 7 mg. Full dose range not given in the abstract; see the paper (Intranasal, single doses)
• Rosen RC 2004: 0.3 to 10 mg in healthy men; placebo, 4 mg or 6 mg in a crossover design in men with erectile dysfunction (Subcutaneous, single doses)
• Diamond LE 2006: 20 mg single intranasal dose, or placebo, in a double-blind crossover design (Intranasal, single dose; Two in-clinic sessions, with responses recorded over the following 24 hours)
• Clayton AH 2016: 0.75 mg, 1.25 mg or 1.75 mg, or placebo, self-administered as desired (Subcutaneous, self-administered as desired; 12 weeks)
• White WB 2017: 0.75 mg, 1.25 mg or 1.75 mg, or placebo (Subcutaneous)

Every study

Bremelanotide is thought to act in the brain rather than on the genitals. The supporting findings:

• Melanocortin receptors: it activates MC3R and MC4R, receptors involved in appetite, sexual behaviour and other functions (Diamond 2006).
• Desire rather than reflexes: in female rats it increased behaviours linked to sexual motivation but not reflexive sexual responses, which points to a central effect (Pfaus 2004).
• No measurable change in genital blood flow: in women, a single dose did not change vaginal blood flow during erotic videos, even though desire ratings rose (Diamond 2006).
• Blood pressure: drugs that activate MC4R may raise blood pressure, which is the proposed reason for the small rises seen after dosing (White 2017).

1. Wash your hands and work on a clean, uncluttered surface. Let a refrigerated vial reach room temperature so the stopper is easier to pierce.
2. Wipe the rubber stopper of the peptide vial and of the bacteriostatic water with a fresh alcohol swab, and let them air-dry.
3. Draw the chosen volume of bacteriostatic water into a sterile syringe. With 2 mL, a 10 mg vial ends up at 5,000 mcg/mL, or 50 mcg per U-100 unit.
4. Insert the needle through the stopper and let the water run slowly down the inside wall of the vial, not straight onto the powder.
5. Swirl or roll the vial gently until the powder dissolves. Do not shake it: foaming can damage some peptides.
6. Check the solution against the light. It should be clear; cloudiness or particles mean something is wrong with the vial or the water.
7. Write the date and the volume of water on the label. Every unit calculation later depends on that volume.
8. Store the reconstituted PT-141 vial in the refrigerator, away from light.

• A U-100 insulin syringe holds 1 mL in 100 units, so each unit is 0.01 mL. The marks measure volume, not peptide.
• Syringes come in 0.3 mL (30 units), 0.5 mL (50 units) and 1 mL (100 units) sizes. The smaller ones have finer marks and are easier to read for small volumes.
• Read the volume at the top edge of the plunger's rubber seal, at eye level.
• Tap out air bubbles before reading: a bubble takes up volume and makes the reading wrong.
• Use a new sterile syringe and needle every time, and dispose of them in a sharps container.

• The peptide vial, with its certificate of analysis (COA) for that batch. See how to read a COA.
• Bacteriostatic water (water with 0.9% benzyl alcohol), which keeps a multi-use vial from growing bacteria. Sterile water has no preservative.
• Sterile syringes to add the water, and U-100 insulin syringes to measure.
• Alcohol swabs for the stoppers.
• A sharps container for used needles.
• A label or marker to write the date and the volume of water on the vial.

Because it is an approved drug, bremelanotide's side effects are better documented than those of most peptides. In the double-blind phase 3 trials, side effects were common and were the main reason people stopped (Clayton 2022). The FDA prescribing information lists uncontrolled high blood pressure and known cardiovascular disease as reasons not to use it.

• Nausea, flushing and headache: nausea affected 40.0% on bremelanotide versus 1.3% on placebo, flushing 20.3% versus 1.3%, and headache 11.3% versus 1.9% (Clayton 2022). An independent analysis found that the odds of dropping out because of side effects were about 12 times higher on the drug than on placebo (Spielmans 2021).
• Blood pressure and heart rate: systolic blood pressure rose by about 2 to 3 mmHg compared with placebo in the hours after a dose, with a fall in heart rate; peaks usually lasted under 15 minutes (White 2017).
• Skin darkening (focal hyperpigmentation): rare at the doses used in the phase 3 trials, but it occurred in more than a third of people given up to 16 daily doses in a row (Clayton 2022). The FDA label notes it can affect the face, gums and breasts, is more likely with darker skin and daily dosing, and did not always resolve.
• Drug interactions: it lowered blood levels of the painkiller indomethacin and of naltrexone, a medicine used for alcohol and opioid dependence (Clayton 2022).
• Product quality: products sold online as "PT-141" are not Vyleesi. No regulator checks their identity, purity, dose or sterility, and none of the trial results above apply to them automatically.
• Sport: we could not find bremelanotide named on the 2026 WADA Prohibited List. That list is not exhaustive, so athletes should check with their anti-doping organisation.

Before mixing

• Freeze-dried (lyophilised) peptide is the most stable form. It is usually kept refrigerated, or frozen for long storage, sealed and away from light.
• Heat, moisture and light speed up degradation. Keep the vial in its box and avoid leaving it in a car or by a window.

After mixing

• Keep the reconstituted vial refrigerated and away from light. Do not freeze it again: freezing and thawing a solution can break the peptide down.
• How long a mixed vial stays good depends on the peptide and the diluent, and for most research peptides there is no published stability data. Follow the supplier's guidance and discard any vial that turns cloudy.
• Pierce the stopper as few times as possible, and always with a new sterile needle after wiping it with alcohol.
• Write the volume of water on the label (for example "2 mL"). Without it, the unit calculations cannot be checked later.