PT-141 vs Kisspeptin: differences, evidence and safety

Verdict: PT-141 (bremelanotide) is an FDA-approved drug, Vyleesi, for low sexual desire in premenopausal women, backed by two phase 3 trials. Kisspeptin is not approved for any use; its best evidence is small crossover trials showing changes in sexual brain responses during a single lab infusion.

PT-141 is the development name of bremelanotide, which the FDA approved in 2019 as Vyleesi for acquired, generalized hypoactive sexual desire disorder (HSDD, persistent low desire that causes distress) in premenopausal women [Approved label] (Vyleesi prescribing information). Kisspeptin is a natural hormone that switches on the reproductive axis; in randomized crossover trials of 32 women and 32 men with HSDD, it changed how the brain responded to erotic videos [Human RCT] (Thurston 2022; Mills 2023). Those trials used an intravenous form, kisspeptin-54, not the kisspeptin-10 sold online, which FDA lists among compounding substances that may pose significant safety risks (FDA). In trials, 40% of women on Vyleesi had nausea; kisspeptin’s long-term safety is unknown.

Item	PT-141 (bremelanotide)	Kisspeptin
US FDA status	Approved June 21, 2019 as Vyleesi, premenopausal women with acquired, generalized HSDD only; not for men or postmenopausal women (Drugs@FDA)	Not approved for any use; no FDA-approved kisspeptin product
Compounding (503A/503B)	Not on FDA’s Category 2 list; “PT-141” sold online was called an unapproved new drug in an FDA warning letter dated August 24, 2026 (FDA)	Kisspeptin-10 in Category 2 (503A) since September 29, 2023, for immunogenicity and impurity risks; still listed, no change announced (FDA)
WADA 2026	Not named on the 2026 List (WADA)	Prohibited at all times in males: S2.2.1 names “kisspeptin and its agonist analogues”
Strongest evidence	Approved label; two phase 3 RCTs (n=1,267)	Human RCTs, crossover, single infusion (n=32 each)
Human trials	NCT02333071, NCT02338960, NCT04179734	Sexual-desire trials registered outside ClinicalTrials.gov; fertility trials e.g. NCT01667406, NCT05896293
Last checked	2026-10-04	2026-10-04

PT-141 vs kisspeptin at a glance

Feature	PT-141 (bremelanotide)	Kisspeptin
What it is	Synthetic analogue of alpha-melanocyte-stimulating hormone (Dhillon 2019)	Natural hormone; studied as kisspeptin-54 and kisspeptin-10
Class	Melanocortin receptor agonist	Kisspeptin receptor agonist (reproductive neuropeptide)
Main receptor	MC4R and MC1R most relevant (label)	Kisspeptin receptor on GnRH neurons
Main research focus	Low sexual desire in women; erectile response in men	Fertility, hypothalamic amenorrhea, low sexual desire
Human evidence for desire	Two phase 3 RCTs, 1,267 women (Kingsberg 2019)	Two crossover RCTs, 32 women and 32 men (Thurston 2022; Mills 2023)
Main outcome measured	Questionnaire scores for desire and distress over 24 weeks	Brain scan responses during a 75-minute infusion
Approval status	FDA-approved (Vyleesi); not EU-authorised	No approval found at FDA or EMA
WADA	Not named	Prohibited in males (S2.2.1)
Routes studied	Under-the-skin injection	Intravenous, under-the-skin, nasal spray
Timelines in studies	Peak blood level about 1 hour; desire raised up to 24 hours	Brain and penile responses within a 75-minute infusion
Main safety concerns	Nausea, flushing, headache, blood pressure rise, skin darkening	No adverse events in short trials; long-term unknown; desensitization with frequent use

What is PT-141?

PT-141 is bremelanotide, a seven-amino-acid peptide first developed by Palatin Technologies as an analogue of alpha-melanocyte-stimulating hormone, a natural hormone that acts on melanocortin receptors in the brain and skin (Dhillon 2019). As Vyleesi, it is an as-needed injection for premenopausal women with acquired, generalized HSDD that is not caused by another medical condition, a relationship problem or a medication [Approved label]. The label states it is not indicated for men, for postmenopausal women or “to enhance sexual performance” (Vyleesi label). Products sold online as “PT-141” are not Vyleesi; FDA has treated them as unapproved drugs.

What is kisspeptin?

Kisspeptin is a natural hormone that activates the brain cells releasing gonadotropin-releasing hormone (GnRH), which in turn drives luteinizing hormone (LH), follicle-stimulating hormone and sex hormones (Mills 2025, EBioMedicine). Imperial College London researchers have tested it mainly for fertility: in a phase 2 trial of 60 women at high risk of ovarian hyperstimulation syndrome, a single kisspeptin-54 injection triggered egg maturation in 95% of them [Human RCT, n=60] (Abbara 2015). The sexual-desire research is newer and comes mainly from the same Imperial group. Kisspeptin-10, the shorter fragment sold online, has been tested in people mainly for its hormone effects (Yeung 2026).

How they work differently

• Target. PT-141: activates several melanocortin receptors, with MC1R and MC4R most relevant at treatment doses; “the mechanism by which Vyleesi improves HSDD in women is unknown” (Vyleesi label). Kisspeptin: acts upstream of GnRH and raises LH within the infusion window [Human RCT, n=95] (Mills 2025).
• Hormones. PT-141: acts on melanocortin receptors, and neurons carrying MC4R are found in many areas of the central nervous system (label). Kisspeptin: stimulates the reproductive axis; subcutaneous kisspeptin-10 raised LH, follicle-stimulating hormone and testosterone in 15 healthy men [Human, randomized, n=15] (Yeung 2026).
• Brain effects. PT-141: in 31 women with HSDD, bremelanotide changed brain activity to erotic images and strengthened amygdala–insula connectivity [Human RCT, n=31] (Thurston 2022, JCI). Kisspeptin: in 29 healthy men, it enhanced limbic brain activity to sexual and couple-bonding images at a dose chosen to avoid a testosterone rise during scanning [Human RCT, n=29] (Comninos 2017).
• Skin. PT-141: MC1R activation on pigment cells explains the skin darkening seen with repeated use (label). Kisspeptin: no pigment effect reported.
• A link between the systems. In female mice, the melanocortin receptor MC4R sits on kisspeptin neurons and is needed for normal fertility [Animal] (Talbi 2025). Whether this matters for desire in people is untested.

Evidence head-to-head

Outcome	PT-141 best evidence	Kisspeptin best evidence
Sexual desire score, women	Human RCT (n=1,267): +0.35 vs placebo on a 1.2–6 scale (Kingsberg 2019)	Not a primary outcome; brain responses changed (Thurston 2022)
Distress about low desire	Human RCT: −0.33 vs placebo (Kingsberg 2019)	Not a primary outcome; hippocampal response correlated with baseline distress (r=0.469), Human RCT (n=32)
Satisfying sexual events	No difference vs placebo in phase 3 (label); +0.7 vs +0.2 per month in phase 2b (Clayton 2016)	Not measured
Men: desire or arousal	Human, early phase: erectile response in men with ED (Rosen 2004); not approved for men	Human RCT (n=32): penile response up to 56% above placebo; more “happiness about sex” (Mills 2023)
Brain responses	Human RCT (n=31) (Thurston 2022, JCI)	Human RCTs (n=29 to 32) (Comninos 2017)
Long-term use	52-week open-label extension, 684 enrolled (Simon 2019)	None for desire

The gap is large. Vyleesi’s benefit rests on two large 24-week trials, although an independent reanalysis found that 72.72% of protocol-listed outcomes went unreported and judged the gains “modest” (Spielmans 2021). Kisspeptin’s results are encouraging but early: each trial gave one 75-minute infusion in a scanner, measured brain responses rather than everyday sexual function, and was run by one research group. The evidence levels used in this table follow our method for comparing peptides.

Which fits which goal?

PT-141 has more evidence for premenopausal women with acquired, generalized HSDD: it is the only one of the two with an approved label, and its phase 3 trials showed statistically significant gains in desire and distress scores [Human RCT, n=1,267] (Kingsberg 2019). Kisspeptin has more evidence for reproductive hormone problems, such as triggering egg maturation in IVF (Abbara 2015). For low desire in men, kisspeptin has the only randomized data of the two, from a single trial of 32 men (Mills 2023), while the Vyleesi label excludes men. For postmenopausal women, neither has an approved use. These are statements about evidence, not recommendations; a clinician is the person to decide whether any treatment fits.

Can they be combined?

Combining the two is discussed online, and the idea has a biological basis: in mice, melanocortin signaling reaches kisspeptin neurons [Animal] (Talbi 2025). No controlled human study has tested the combination, and no registered trial combines them. The Vyleesi label also warns that bremelanotide may slow stomach emptying and lower blood levels of oral naltrexone, so interactions with other drugs are a real issue (Vyleesi label).

Safety and regulatory status

PT-141 side effects. In the integrated phase 3 data (n=1,247), nausea affected 40.0% on bremelanotide vs 1.3% on placebo, flushing 20.3% vs 1.3% and headache 11.3% vs 1.9% (Clayton 2022). The label adds a transient blood pressure rise of up to 6 mmHg systolic, peaking 2 to 4 hours after a dose; focal skin darkening of the face, gums or breasts in 1% of trial users, and in 38% after daily use for 8 days in another study; and one case of acute hepatitis in the open-label extension. It is contraindicated with uncontrolled high blood pressure or known heart disease (Vyleesi label). The independent reanalysis put the odds of stopping for side effects at 11.98 times placebo (Spielmans 2021).

Kisspeptin side effects. The short trials reported none: no adverse events in women or men with HSDD (Thurston 2022; Mills 2023), and no change in anxiety, cortisol, blood pressure or heart rate in 95 volunteers [Human RCT] (Mills 2025). In these trials, each participant received a single 75-minute infusion, so longer-term safety is unknown. Frequent repeated injections in women with hypothalamic amenorrhea made the hormone response fade, a sign of desensitization (Jayasena 2010). FDA flags immunogenicity and impurity risks for compounded kisspeptin-10 (FDA Category 2 list).

United States. Vyleesi is a prescription drug (Drugs@FDA). Online “PT-141” is a different matter: FDA named it among unapproved new drugs in a 2026 warning letter to a seller (FDA warning letter). Kisspeptin has no approval, and kisspeptin-10 remains in Category 2 for 503A compounding, alongside ipamorelin acetate for 503B, which is compared in ipamorelin vs sermorelin vs tesamorelin. More on how FDA treats unapproved peptides is in our overview, Are peptides safe?

European Union. Neither appears in EMA’s list of authorised medicines (EMA).

Sport. The WADA 2026 List prohibits “kisspeptin and its agonist analogues” in males at all times under S2.2.1; bremelanotide is not named (WADA 2026 List). Athletes should check any product with their anti-doping organization.

How long do effects take in studies?

For PT-141, blood levels peak about 1 hour after an injection and the half-life is about 2.7 hours; the label says to stop after 8 weeks if a woman reports no improvement (Vyleesi label). In the Imperial study, desire stayed higher than placebo for up to 24 hours after a dose (Thurston 2022, JCI). The phase 3 results were measured at 24 weeks (Kingsberg 2019). For kisspeptin, brain and penile responses were recorded during a 75-minute infusion, before testosterone changed (Mills 2023), and a nasal spray raised LH rapidly (Mills 2025, EBioMedicine). No study has followed kisspeptin’s effect on desire over weeks.