PT-141

What PT-141 is and how it works

PT-141 is the development code for bremelanotide, a cyclic seven-residue peptide almost identical to melanotan II. The ring is the same; the difference sits at the C-terminus, where bremelanotide ends in a free acid instead of an amide. That single change adds about 1 Da to the mass, 1025.2 against 1024.2, and marks where the two compounds took different paths. The US company Palatin Technologies developed bremelanotide after early work with melanotan II showed that a melanocortin agonist could trigger erections through the brain rather than through local blood flow.

Bremelanotide activates melanocortin receptors. The US label describes it as a non-selective agonist with an order of potency of MC1R, MC4R, MC3R, MC5R and MC2R, and states that binding to MC1R and MC4R matters most at therapeutic doses. Neurons carrying MC4R are spread through the central nervous system, including regions involved in sexual motivation, and it is through those pathways that the drug is thought to act. The panel lists MC4R and MC3R because they carry the intended effect; the label makes clear that MC1R is engaged as well, which is why skin and gums can darken.

The approach is the mirror image of the PDE5 inhibitors. Sildenafil and its relatives work on blood vessels and need sexual stimulation to do anything; bremelanotide is given in advance and acts on signalling in the brain. An early nasal-spray formulation ran into rises in blood pressure, and that programme was halted in 2008 before development moved to a subcutaneous injection with more consistent blood levels. Even now, the label states that the mechanism by which the drug improves low sexual desire is unknown.

What the research on PT-141 shows

Approval rested on two identically designed phase 3 trials: randomised, double-blind and placebo-controlled, with a 24-week core phase and a 52-week open-label extension. Together they enrolled 1,247 premenopausal women with acquired, generalised hypoactive sexual desire disorder, who used the injection as needed before anticipated sexual activity. The co-primary end points were change in the desire domain of the Female Sexual Function Index and change in distress about low desire. Bremelanotide beat placebo on both, in both trials.

The secondary end point gets less attention: the number of satisfying sexual events did not differ significantly between the groups. What reached statistical significance was measured on questionnaire scales, and the differences were modest. That is the evidence base behind the approval, and still far more than exists for most peptides on this site.

The 2019 approval covers premenopausal women with acquired, generalised hypoactive sexual desire disorder not caused by a medical or psychiatric condition, by relationship problems or by a medicine. It is not approved for postmenopausal women or men, although bremelanotide was studied earlier in men with erectile dysfunction.

PT-141 doses used in published research

These figures are what the US label states for an authorised medicine used under prescription in a defined group of patients. They describe that product, not research material sold by weight in a vial, and they are recorded as label and study information, not as instructions for use. No equivalent dose has been authorised in the EU.

PT-141 safety and side effects

Because bremelanotide went through a full trial programme, its adverse effects are quantified rather than guessed at. The figures below are from the US label.

• Nausea. The most common adverse event, in 40.0% of women on bremelanotide against 1.3% on placebo. Around 8% stopped treatment because of it.
• Flushing and headache. Flushing affected 20.3% against 0.3% on placebo, headache 11.3% against 1.9%. Injection-site reactions and vomiting were also more frequent than with placebo.
• Blood pressure and heart rate. Each dose transiently raises blood pressure, by up to 6 mmHg systolic and 3 mmHg diastolic, and lowers heart rate by up to 5 beats per minute, with values back to baseline within 12 hours. The label contraindicates use in uncontrolled hypertension or known cardiovascular disease.
• Focal hyperpigmentation. Darkening of the face, gums or breasts occurred in 1% of trial patients taking up to eight doses a month, and in 38% of participants dosed daily for eight days in a separate study. It did not resolve in every patient after stopping.
• Naltrexone. Bremelanotide can markedly reduce exposure to oral naltrexone, and the label advises against taking the two together.

Regulatory status of PT-141 in Europe

Bremelanotide is approved in the United States and has no marketing authorisation in the EU. The European Medicines Agency has not authorised it, so there is no European Vyleesi, no EU product information and no European assessment of its benefits and risks. Material sold in Europe as PT-141 is a research chemical: not the US medicine, not authorised, not for human use. Our primer on research peptides explains how far apart those categories sit.

Under EU law a substance presented for treating a condition, or used to modify a physiological function by pharmacological action, is a medicinal product and requires authorisation before it may be placed on the market. Rules on possession and personal import differ between member states. In sport, the WADA S0 category covers substances with no approval for human therapeutic use anywhere, which does not apply to a compound approved in the United States; athletes should still check the current Prohibited List.

Sourcing and quality of PT-141

King Peptides does not stock PT-141. The closest product in its range is Melanotan II 10 mg, and it needs to be taken for what it is: a different compound, not research-grade bremelanotide. Melanotan II shares the ring but ends in an amide, has its own non-selective profile across MC1R, MC3R, MC4R and MC5R, and never completed a clinical development programme. Results obtained with one cannot be assigned to the other.

For any melanocortin peptide, the certificate of analysis is where identity is settled. Look for HPLC purity of 99% or higher, a lot number matching the vial, and a mass spectrum precise enough to separate 1025.2 Da from the 1024.2 Da of melanotan II. King Peptides dispatches from the Netherlands, with a shop estimate of 1–2 business days within the Netherlands and 3–5 business days elsewhere in the EU and no customs formalities inside the union; parcels to the UK, Switzerland or Norway can be subject to import rules and duties. Orders are neutrally packed and tracked, and buyers confirm at checkout that they are 18 or older and ordering for research. See our guide to reading a certificate of analysis and our storage and reconstitution guide.

PT-141: frequently asked questions

Is PT-141 the same thing as Vyleesi? The molecule is the same, bremelanotide. Vyleesi is the approved US product: an autoinjector made, tested and released under pharmaceutical rules. Research powder shares the sequence and none of that status.

Does it work like sildenafil? No. Sildenafil acts on blood vessels and depends on sexual stimulation. Bremelanotide acts on melanocortin receptors in the brain, which is also why its side effects are systemic rather than local, blood pressure among them. That is why the label rules out uncontrolled hypertension or known cardiovascular disease.

Can melanotan II stand in for PT-141 in research? Not for questions about bremelanotide. It is a related but distinct compound with a different receptor balance, a different regulatory status and a thinner evidence base.