PT-141

What is PT-141?

PT-141 is the research code for bremelanotide, a synthetic peptide sold in the US as Vyleesi. It is one of only two drugs the FDA has approved for hypoactive sexual desire disorder (HSDD), a condition defined by persistently low sexual desire that causes distress and is not explained by another medical problem, relationship issue or medication. Its approved use is narrow: premenopausal women with acquired, generalized HSDD.

The compound grew out of melanotan II, a peptide first studied as a tanning agent. Researchers noticed that melanotan II produced sexual arousal as a side effect, and bremelanotide was developed to pursue that effect. Palatin Technologies originally developed PT-141 as a nasal spray for both erectile dysfunction and female sexual dysfunction, and had completed a phase IIb trial in men with erectile dysfunction by 2003¹. The nasal program was later dropped amid concerns about blood pressure, and the product that reached market is a self-administered subcutaneous injection used on demand. Palatin ran the phase 3 trials and licensed North American rights to AMAG Pharmaceuticals, which filed for approval². The FDA approved it in 2019.

Outside its approved use, PT-141 is widely sold online as a research chemical and promoted for libido in men and women, including as an alternative for men who do not respond to erectile dysfunction pills.

How PT-141 works

Most sexual dysfunction drugs that people know about, such as sildenafil, work on blood flow. PT-141 works in the brain instead. It switches on a signaling system called the melanocortin system, which helps regulate appetite, skin pigment and sexual motivation. By nudging the brain circuits involved in desire, it aims to increase interest in sex rather than to produce a physical response directly. That is why it is aimed at low desire, not at a mechanical problem with arousal.

In more precise terms, bremelanotide is a cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone (alpha-MSH) with high affinity for the melanocortin-4 receptor (MC4R)². It is closely related to melanotan II, differing mainly at the C-terminus, a change that reduces activity at MC1R, the receptor that drives skin darkening. MC4R is expressed in hypothalamic and limbic areas that shape sexual motivation. Agonism there is thought to shift the balance between excitatory and inhibitory inputs to desire, consistent with the dual-control model of sexual response used to describe HSDD³. The same melanocortin system is the target of setmelanotide for genetic obesity and afamelanotide for a rare light-sensitivity disorder, and a 2023 review cites these approvals as evidence that peptides in this class can be developed safely⁴.

What the research shows on PT-141

The strongest evidence comes from the phase 3 program in premenopausal women that supported approval. A review of the two phase 3 reports and two phase 2 reports found that bremelanotide produced statistically significant improvements in sexual desire and significant reductions in distress about low desire compared with placebo⁸. The same review cautioned that, although the trials met statistical significance, the clinical benefit may be modest⁸. In practical terms, many women in the trials did not notice a large change, and some on placebo improved too.

Reviews of female sexual dysfunction treatment place bremelanotide alongside flibanserin as the two centrally acting options for HSDD in premenopausal women, with transdermal testosterone the better-studied option after menopause⁷. Other reviews describe the safety data for these approved medicines as strengthening over time⁶. There is also ongoing debate about how female sexual disorders are diagnosed, since the DSM-5 merged desire and arousal disorders into one category, which complicates how trial results apply to individual patients⁵.

Evidence in men is thinner. Early trials explored erectile dysfunction, including in men who did not respond to PDE5 inhibitors, but that program did not lead to approval and there is no large modern trial base for male use. Claims about male libido, enhanced orgasm or use alongside sildenafil rest on small early studies and anecdote, not on the kind of evidence that supported the female indication.

Studied for: Hypoactive sexual desire disorder in premenopausal women, Erectile dysfunction research.

PT-141 reference data

PT-141 dosage in published research

How PT-141 is used in practice

As a prescription drug, Vyleesi comes as a single-dose autoinjector that the patient uses under the skin of the abdomen or thigh about 45 minutes before anticipated sexual activity⁸. Prescribing information limits use to no more than one dose in 24 hours and no more than eight doses a month, and advises stopping after eight weeks if there is no benefit⁸. It is an on-demand drug, not a daily one, which some patients prefer to flibanserin's nightly pill.

Cost, patchy insurance coverage and the need to inject are practical barriers.Some telehealth services prescribe it for women who meet the HSDD criteria. Other clinics and online sellers offer compounded or unbranded bremelanotide to men and women off label, often in multi-dose vials. Products sold as research chemicals are not made to pharmaceutical standards. Their identity, purity, sterility and dose are not verified, and because PT-141 and melanotan II are chemically close, mislabeling between them is a realistic concern.

PT-141 risks and side effects

Nausea is the most common side effect, reported by about 40% of trial participants, followed by facial flushing in about 20% and headache in about 11%⁸. Nausea is usually worst after the first dose and tends to ease with later doses. Injection-site reactions are also common.

Bremelanotide causes a transient rise in blood pressure and a small drop in heart rate after each dose, which usually resolves within about 12 hours. For that reason it is not recommended for people with uncontrolled high blood pressure or known cardiovascular disease. Repeated use can cause focal darkening of the skin, gums or face, which may not fully reverse. The label also warns that it can lower blood levels of oral naltrexone, a concern for anyone taking naltrexone for alcohol or opioid dependence. It may slow stomach emptying and affect absorption of other oral drugs.

The review literature describes limited drug interactions and no clinically significant interaction with alcohol⁸. It should not be used in pregnancy. Long-term data on frequent use beyond the trial periods are limited, and none of the trial safety data apply to unregulated products of unknown content.

Reported side effects

Alternatives to PT-141

For premenopausal women with HSDD, the main approved alternative is flibanserin (Addyi), a daily oral tablet that acts on serotonin and dopamine signaling. It requires daily use and carries warnings about low blood pressure and fainting, particularly with alcohol. After menopause, transdermal testosterone at doses appropriate for women has the strongest evidence for desire, and menopausal hormone therapy is the mainstay for midlife symptoms that affect sexual function⁷.

Non-drug approaches matter too. Clinicians are advised to take a biopsychosocial approach, looking at medications such as SSRIs, relationship factors, depression and pain before reaching for a drug³. Sex therapy and cognitive behavioral therapy have evidence for low desire.

For men with erectile dysfunction, PDE5 inhibitors such as sildenafil and tadalafil are approved, well studied and inexpensive. Men with low desire should be checked for low testosterone, depression, medication effects and other medical causes, since PT-141 is not approved for any male indication.

Questions for a clinician

• What evidence applies to my situation, and at what level?
• What established alternatives should I consider first?
• What monitoring would be necessary, and how often?