Kisspeptin and PT-141 are searched together because both are sold as "libido peptides". They reach that claim from different directions and with different evidence. PT-141 is bremelanotide, an approved drug with one labelled dose. Kisspeptin is a hormone that sits at the top of the reproductive axis; its studies in low desire are brain-imaging experiments with a different form of the molecule than the one sold in vials.
The single-compound records are on the kisspeptin-10 dosage page and the PT-141 dosage page.
| Kisspeptin-10 | PT-141 (bremelanotide) | |
|---|---|---|
| Receptor | KISS1R (GPR54), upstream of GnRH | Melanocortin receptors, chiefly MC1R and MC4R at label doses |
| Approved product | None | Vyleesi, US |
| Labelled dose | None | 1.75 mg subcutaneous, as needed |
| Molecular weight | 1,302.4 | 1,025.2 |
| Desire trials | Kisspeptin-54 infusions, 32 women and 32 men | Two phase 3 trials, 1,267 women |
| What the trials measured | Brain activity on imaging; tumescence in men | Desire and distress scores over 24 weeks |
| Studied together | Never (registry and PubMed, 2026-10-09) | Never |
Two receptors, two jobs
Kisspeptin is the signal that starts the reproductive hormone cascade. It acts on KISS1R in the hypothalamus, which releases GnRH, and the pituitary answers with LH and FSH; in men testosterone follows. How that upstream step compares with giving GnRH itself is on the kisspeptin and gonadorelin comparison. That is why most kisspeptin studies measure hormones, and why its registered trials are physiology studies in reproductive disorders, not sexual-function trials.
Bremelanotide works on a different system. Its label calls it a non-selective melanocortin-receptor agonist for which binding at MC1R and MC4R is most relevant at therapeutic doses, and states that "the mechanism by which VYLEESI improves HSDD in women is unknown". MC1R sits on the pigment cells of the skin, which is where the label's hyperpigmentation finding comes from. Bremelanotide does not act through the reproductive hormones, and the label lists nausea in 40% of patients and a transient blood-pressure rise among its common effects.
Kisspeptin-54 is not kisspeptin-10
The two trials searched for as "kisspeptin for libido" both gave kisspeptin-54, the 54-amino-acid form, as a 75-minute intravenous infusion at 1 nmol/kg per hour against a placebo infusion. In 32 women with hypoactive sexual desire disorder, kisspeptin changed activity in brain regions involved in sexual and attraction processing, and the changes correlated with baseline distress (Thurston et al., 2022). In 32 men with the same diagnosis, it changed activity in the sexual-processing network and increased penile tumescence in response to sexual videos (Mills et al., 2023). Both trials ran at one university in London and lasted one visit per arm.
Kisspeptin-10 is the 10-amino-acid fragment at the end of that molecule. Its human studies are hormone studies: intravenous boluses of 0.01 to 3 mcg/kg in men and pump infusions under the skin. One study found no gonadotropin response at all in women in the follicular phase after boluses of up to 10 nmol/kg intravenously and 32 nmol/kg under the skin, as set out on the kisspeptin-10 page. No trial has measured sexual desire on kisspeptin-10.
PT-141's record, and its own brain-imaging study
Bremelanotide's evidence is two phase 3 trials, RECONNECT, in which 1,267 premenopausal women with hypoactive sexual desire disorder used 1.75 mg as needed or placebo for 24 weeks (Kingsberg et al., 2019). The label's limits come from those trials and from a daily-dosing study: one dose per 24 hours, no more than 8 a month, because focal hyperpigmentation appeared in 38% of women after 8 consecutive daily doses against 1% at the monthly limit.
The group that ran the kisspeptin trials also registered a bremelanotide study with the same design: a placebo-controlled crossover in women with hypoactive sexual desire disorder, 1.75 mg by autoinjector, brain imaging during erotic videos as the main outcome (NCT04179734). Results for 31 women were posted to the registry on 2024-08-09 as group means of a brain-signal coefficient, 9.98 on bremelanotide against 7.67 on placebo, with no statistical test reported. PubMed listed no paper from it on 2026-10-09. It is the closest thing to a like-for-like comparison of the two compounds, and it compares nothing directly: the trials enrolled different women at different times.
Per molecule, PT-141's dose is far larger
| Amount | Molecular weight | Molecules (nmol) |
|---|---|---|
| Kisspeptin-10 100 mcg | 1,302.4 | ≈77 |
| Kisspeptin-10 250 mcg | 1,302.4 | ≈192 |
| Kisspeptin-54 infusion, 70 kg (≈0.51 mg over 75 min, IV) | 5,857 | ≈87.5 |
| PT-141 1.75 mg (label) | 1,025.2 | ≈1,707 |
The labelled bremelanotide dose carries about 22 times as many molecules as 100 mcg of kisspeptin-10. The comparison shows scale only; the two act on different receptors, and only bremelanotide's figure comes from a trial of the route it is sold for.
Each figure as syringe units
| Amount | 2.5 mg/mL | 5 mg/mL | 10 mg/mL |
|---|---|---|---|
| Kisspeptin-10 100 mcg | 4 units | 2 units | 1 unit |
| Kisspeptin-10 250 mcg | 10 units | 5 units | 2.5 units |
| PT-141 1 mg | 40 units | 20 units | 10 units |
| PT-141 1.75 mg | 70 units | 35 units | 17.5 units |
2.5 mg/mL is a 5 mg vial with 2 mL of water; 5 mg/mL is a 10 mg vial with 2 mL; 10 mg/mL is a 10 mg vial with 1 mL. Vyleesi itself is a ready-made solution of about 5.8 mg/mL in a single-dose autoinjector, so the label's 0.3 mL carries no unit marking. At 10 mg/mL a 100 mcg kisspeptin-10 amount is a single unit, smaller than most barrels can mark; the barrels are set out on insulin syringe units, and any vial and volume are worked on the kisspeptin-10 calculator and the bremelanotide vial arithmetic.
What is not established
No trial has compared the two, given them together, or tested kisspeptin-10 for desire. The kisspeptin desire data are single infusions of kisspeptin-54 in a hospital, measured on brain scans; whether a repeated injection of either form changes desire over weeks has not been studied. Bremelanotide's approval covers premenopausal women only. FDA placed kisspeptin-10 in Category 2 of its bulk-substance list in 2023. The compounds are covered in Medibact's Kisspeptin-10 guide and PT-141 guide. Nothing on this page is an instruction; product and dose belong with a prescriber.
Sources and dates
Opened 2026-10-09: the Vyleesi label section 12.1 (openFDA, version effective 2025-11-13); ClinicalTrials.gov searches (kisspeptin AND bremelanotide, 0; bremelanotide, 10; kisspeptin, 36) and the NCT04179734 record with its posted results; PubMed searches and the abstracts of Thurston et al. 2022 (PMID 36287566) and Mills et al. 2023 (PMID 36735255); PubChem records for bremelanotide (CID 9941379), kisspeptin-10 (CID 25240297) and kisspeptin-54 (metastin, CID 71306396). Carried from this site's pages, each with its read date: the Vyleesi label, RECONNECT and the hyperpigmentation figures (PT-141 page, 2026-09-18), and the kisspeptin-10 human studies and FDA category (kisspeptin-10 page, 2026-09-18). Units and molar arithmetic by this site. Corrections go to the contact page.