PT-141 vs Kisspeptin
PT-141 is bremelanotide, FDA approved as Vyleesi for low sexual desire in premenopausal women. Kisspeptin sits above the hormone axis and raises LH, FSH and testosterone. They address different problems. PT-141's trials showed a real but modest effect that four in ten women quit before finishing, and kisspeptin stops working within two weeks on the daily schedule most sources recommend.
- Sexual and hormonal
- One is FDA approved
- Different problems entirely
One works on desire. One works on hormones.
Both are sold for sex. Only one is approved, for one condition in one population, and the other stops working on the schedule most pages recommend.
| Attribute | PT-141 | Kisspeptin |
|---|---|---|
| Proper name | Bremelanotide, brand Vyleesi | Kisspeptin-10 or kisspeptin-54 |
| What it acts on | Melanocortin receptors in the brain | The hormone axis, upstream of GnRH |
| What it changes | Desire | LH, FSH and testosterone |
| FDA status | Approved June 2019 [1] | Not approved anywhere |
| Human trials | Two Phase 3, 1,247 patients [2] | Small studies, mostly one research group [8] |
| The catch | 40 percent discontinued [1] | Stops working in two weeks on daily dosing [8] |
Vyleesi is approved for one condition in one population. Research-grade PT-141 is not that product.
PT-141
A melanocortin peptide derived from Melanotan II. It acts on receptors in the brain, not on tissue anywhere else in the body. In plain terms: it works on wanting sex, not on the mechanics of it, and you take it before an occasion instead of every day.
Kisspeptin
A peptide that sits above the whole reproductive hormone chain. It tells the hypothalamus to release GnRH, which tells the pituitary to release LH and FSH, which tell the gonads to make testosterone or estrogen. In plain terms: it pulls the lever at the top of the chain.
Both get filed under sexual health. That is most of what they share.
PT-141 works in the brain. It activates melanocortin receptors, mainly MC4R, in pathways involved in sexual desire. It does nothing to blood flow, which is the entire mechanism of the drugs most people compare it to, and it does nothing to hormone levels. The problem it addresses is wanting. If desire is intact and the mechanics are the issue, PT-141 is aimed at the wrong thing.
Kisspeptin works on the hormone axis. It acts on KISS1R and triggers GnRH release, which cascades down to LH, FSH and then testosterone or estrogen. It is the switch above the switch. It has been studied in women whose periods stopped because the axis is suppressed, and in men with low testosterone driven by the same. If hormone levels are normal, there is nothing for it to correct.
And there is a naming problem. Kisspeptin-10 is the ten amino acid active core. Kisspeptin-54 is the full length version, with a subcutaneous half-life of roughly 28 minutes. Most human trial evidence used kisspeptin-54, including the desensitization work below. Most of what is sold is kisspeptin-10. That is the most important finding on this page, and it is the fourth compound in this library where the evidence belongs to a different molecule than the one in the vial, alongside TB-500, Epitalon and sermorelin.
Everything that differs
| Attribute | PT-141 | Kisspeptin |
|---|---|---|
| Full name | Bremelanotide | Kisspeptin-10, kisspeptin-54, metastin |
| Brand | Vyleesi | None |
| Family | Melanocortin, derived from Melanotan II | Kisspeptin, upstream of GnRH |
| Receptor | MC4R and related, in the brain | KISS1R |
| What it changes | Sexual desire | LH, FSH, testosterone and estrogen |
| Effect on hormones | None | That is the entire mechanism |
| Approved | June 2019, premenopausal HSDD [1] | Nowhere |
| Largest evidence | Two Phase 3 trials, 1,247 patients [2] | Studies of 10 to 14 people [8][9] |
| Headline result | 34.6 percent responded against 22.8 percent on placebo [2] | LH response falls from 24.0 to 2.5 over two weeks [8] |
| Dosing | On demand, 1.75 mg, a few times a month [1] | Every published schedule is disputed |
| Nausea | 40.0 percent against 1.3 percent on placebo [3] | Mild, reported in trials |
| Blood pressure | Raises it. Contraindicated in uncontrolled hypertension [1][4] | No reported effect |
| Discontinuation | 40 percent and 39 percent in the two trials [1] | Not applicable |
| Sold as | Research chemical, and as Vyleesi on prescription | Research chemical only |
Four in ten women stopped taking the drug that worked.
Built out of Melanotan II
Bremelanotide is developed from Melanotan II, keeping the effect on sexual arousal and dropping the pigment activity that made Melanotan II unusable as a medicine.
First human work
Dhillo and colleagues at Imperial College London publish the first human work, showing kisspeptin-54 stimulates gonadotropin release. This begins the body of evidence, almost all of it from one research group. [7]
The finding that matters most
Jayasena and colleagues randomize 10 women with hypothalamic amenorrhea to kisspeptin-54 or saline, twice daily for two weeks.
On day one, LH rose by 24.0 IU/L and FSH by 9.1. By day fourteen, the same injection raised LH by 2.5 and FSH by 0.5. Both differences were statistically significant. The response had collapsed by roughly 90 percent while the dose stayed the same. [8]
Spacing the doses out
The same group tests twice weekly dosing over eight weeks to see whether spacing the doses avoids the problem. Desensitization was reduced. Menstruation was not restored. [9]
A dose response that reverses
A study in men finds a dose response up to 1 microgram per kilogram, and then a higher 3 microgram dose producing a smaller LH rise than the lower ones. The authors note that the receptor is known to desensitize rapidly. [10]
The RECONNECT trials
Two identical Phase 3 studies, 1,247 women with acquired generalized hypoactive sexual desire disorder, randomized to 1.75 milligrams of bremelanotide or placebo, taken as needed for 24 weeks.
Both co-primary endpoints were met. Desire scores improved by 0.5 points over placebo and distress scores fell by 0.7, each at p less than 0.001. In the responder analysis, 34.6 percent of treated women reached a meaningful improvement in desire, against 22.8 percent on placebo. [2]
Approved as Vyleesi
The FDA approves bremelanotide as Vyleesi, for acquired generalized HSDD in premenopausal women. [1]
The safety review
A safety review across 43 studies and 3,500 subjects reports nausea in 40.0 percent against 1.3 percent on placebo, flushing in 20.3 percent, headache in 11.3 percent. Nausea was the most common reason people stopped. [3]
Where this leaves them
Vyleesi is prescribed for one condition. Kisspeptin has no approval anywhere, and the schedule most sources recommend is the one shown not to work.
The RECONNECT trials met both endpoints and produced an approval. They also record something the marketing never mentions: 40 percent of women on bremelanotide left the 24 week trial early, against 13 percent on placebo in the first study and 39 against 25 in the second. Nausea was the main reason. None of that makes the approval wrong. It is what an efficacy picture looks like when somebody counts everything. Kisspeptin's problem is different and less visible: almost every source recommends daily or twice daily dosing, and the one controlled trial of twice daily dosing found the response falling by roughly 90 percent over two weeks.
How each one works
PT-141
Melanocortin receptors sit in brain regions involved in arousal and motivation. PT-141 activates them, and the downstream effect appears to involve dopamine release in those pathways.
What it does not do is change blood flow, and it does not change hormone levels. So it goes in about 45 minutes before an occasion instead of every day, and what it addresses is desire, not function.
Its family explains its side effects. PT-141 comes from Melanotan II, and the nausea, flushing and possible skin darkening with repeated use are melanocortin effects the whole family shares. [3] Activating MC4R also produces an adrenergic response that raises blood pressure and heart rate, which is why the label rules out anyone with uncontrolled hypertension or known cardiovascular disease. [4]
Kisspeptin
Kisspeptin acts on KISS1R in the hypothalamus and triggers GnRH release. GnRH drives LH and FSH from the pituitary, and those drive testosterone or estrogen from the gonads.
That is the whole mechanism, and it is also the whole problem. The receptor desensitizes. Give it twice a day and the same injection that raised LH by 24.0 IU/L on day one raises it by 2.5 two weeks later. [8]
There is a second, separate signal: brain imaging work reporting effects on responses to sexual and emotional stimuli, apparently independent of LH. [6] That is the only support the arousal marketing has, and it is imaging, not an outcome.
Four gaps, and one of them is the dose schedule itself
Nobody has found a kisspeptin schedule that works over time.Twice daily fades within two weeks. [8] Twice weekly fades less and did not restore menstruation. [9] Every-other-day dosing circulates widely and has no published trial behind it. How to give this compound so it keeps working is an open question.
Kisspeptin's libido claim has some support, and it is not the hormonal one.Work from the same Imperial College group reports that kisspeptin affects brain responses to sexual and emotional stimuli, apparently independently of its effect on LH. [6] That is the one place the arousal marketing has any footing. It is also brain imaging, not an outcome trial, and it says nothing about a repeated schedule.
Nobody has studied kisspeptin for raising testosterone in healthy men.That application accounts for much of what is sold, and it has no controlled trial behind it. The desensitization data argues against it working over time.
PT-141's male program was never completed.Earlier work in men with erectile dysfunction did find a statistically significant erectile response against placebo, measured objectively rather than by questionnaire, at subcutaneous doses of 4 or 6 milligrams. [5] Those are much larger doses than the 1.75 milligrams approved for women. The program did not continue to approval, and the blood pressure effect is the reason usually given.
One has a label built from 3,500 subjects. The other has small studies.
PT-141, from its label
Everything here is public because an approved drug has to report it.
- Nausea 40.0 percent against 1.3 percent, the most common reason for stopping [3]measured
- Flushing 20.3 percent against 1.3 percent [3]measured
- Headache 11.3 percent against 1.9 percent [3]measured
- Darkening of skin with repeated use, the reason for the frequency cap [1]label
Label contraindications
Hard contraindications on an approved drug's label, not general cautions.
- Uncontrolled high blood pressure or known cardiovascular disease [1][4]contraindicated
- Pregnancy. Effective contraception required, with an exposure registry [1]contraindicated
- Men, and women past menopause. Neither was studied [1]not studied
- Anyone under 18not studied
What you are actually buying
One has an approved product. Neither research vial is it.
- Vyleesi is a manufactured autoinjector on prescriptionrx only
- Kisspeptin sells as KP-10 and KP-54; most trial evidence is on KP-54identity
- Seized peptides tested 5 to 75 percent pure, plus arsenic and lead [11]analysis
- A US lab reported problems in almost 30 percent of samples, including bacteria [12]testing
*Where this page says nothing is established, it means nobody has studied it. It does not mean a compound is safe.
The Vyleesi label caps how often the drug may be used, because it is a melanocortin and repeated activation drives pigment cells. Anyone using research-grade PT-141 without a frequency limit is doing something the label of the approved version specifically restricts. Our guide on reading a certificate of analysis covers what to look for in a research vial.
One approval, narrowly drawn, and one compound with none
Sport. Neither compound is named on the 2026 WADA Prohibited List. Kisspeptin is worth attention anyway, because it raises LH and testosterone, which is exactly what the hormone modulator categories exist to cover. WADA states that absence from the list does not mean a substance is permitted. PT-141 does not change hormone levels, so it has less exposure on that reasoning. If you compete under a testing body, ask that body directly.
PT-141 is approved, for one condition in one population. Acquired, generalized hypoactive sexual desire disorder in premenopausal women. Acquired means the desire was there and went away. Generalized means it is not specific to one partner or situation. It does not cover men, postmenopausal women, or anyone whose difficulty is with function instead of desire. And the approval belongs to Vyleesi, a manufactured autoinjector with a frequency limit and a label. Research-grade PT-141 is nominally the same peptide and none of the rest of it.
Kisspeptin has no approval anywhere. It has been used in research settings and in fertility clinics under trial protocols, and it has never been approved as a medicine in any country. What is sold under the name is a research chemical, in two different molecular lengths, with no verification of which one is in the vial.
Questions people ask
Which one should I take?
They address different problems. PT-141 works on desire and does nothing to hormones. Kisspeptin works on hormones and was studied in people whose axis was suppressed. If your hormone levels are normal, kisspeptin has nothing to correct.
Is PT-141 the same as Vyleesi?
Same peptide, different product. Vyleesi is a manufactured autoinjector on prescription, with a label and a frequency limit. Research-grade PT-141 is not that product.
Does PT-141 work?
In its trials, yes, modestly. 34.6 percent of treated women reached a meaningful improvement in desire against 22.8 percent on placebo. It is also worth knowing that 40 percent of women left the trial early, mostly because of nausea.
Why does kisspeptin stop working?
The receptor desensitizes. In the one controlled trial of twice daily dosing, the LH response fell from 24.0 IU/L on day one to 2.5 by day fourteen on the same dose. Spacing doses out reduced the fade and did not restore periods.
What is the right kisspeptin schedule then?
Nobody knows. Twice daily fails. Twice weekly fades less and did not achieve the clinical goal. Every-other-day protocols circulate widely with no published trial behind them.
Is kisspeptin-10 the same as kisspeptin-54?
No. Kisspeptin-10 is the ten amino acid core, kisspeptin-54 is the full length version. Most human trial evidence, including the desensitization work, used kisspeptin-54. Most of what is sold is kisspeptin-10.
Can men use PT-141?
The approval covers premenopausal women only, and the label says explicitly that it is not for men. Earlier male studies did find an objectively measured erectile response at 4 or 6 milligrams, much higher than the approved 1.75 milligram dose, and that program was never completed. Off-label use is a prescriber's decision and responsibility.
Does PT-141 affect blood pressure?
Yes. Melanocortin agonists raise blood pressure and heart rate through an adrenergic response, and the approved label contraindicates it in anyone with uncontrolled hypertension or known cardiovascular disease. This is the most important safety point on the page, and it is easy to miss when buying research-grade material with no label attached.
The published record
What Europe PMC and ClinicalTrials.gov hold for each, on the same rule.
PT-141 has 134 records to Kisspeptin's 421. 38 original human studies against 117. PT-141 has 10 registered trials to Kisspeptin's 21.
PT-141: FDA: Named as an unapproved new drug
Kisspeptin: FDA: Category 2 · FDA: In category 2 (503A)
The published record
134
Records indexed for PT-141
90 in humans, 38 of them original studies.
10 registered trials, 4 with posted results.
FDA: Named as an unapproved new drug.
Counted from Europe PMC indexing, not read by a person. Human means indexed under humans, which includes reviews and work on human cells. Original studies exclude reviews and lab work on human cells.Last updated 12 September 2026.
The published record
488
Records indexed for Kisspeptin400 papers and 21 trials indexed in detail.
171 in humans, 117 of them original studies.
21 registered trials, 6 with posted results.
FDA: Category 2 · FDA: In category 2 (503A).
Counted from Europe PMC indexing, not read by a person. Human means indexed under humans, which includes reviews and work on human cells. Original studies exclude reviews and lab work on human cells.Last updated 11 September 2026.
What this page is built on
- 01VYLEESI (bremelanotide injection) prescribing information. Initial US approval June 2019. FDA label. Indication: acquired, generalized hypoactive sexual desire disorder in premenopausal women. Contraindicated in uncontrolled hypertension and known cardiovascular disease. Records 40 percent discontinuation on VYLEESI against 13 percent on placebo in Study 1, and 39 against 25 percent in Study 2.
- 02Kingsberg SA, Clayton AH, Portman D, et al. Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials. Obstet Gynecol. 2019;134(5). PMID 31599840. Human Phase 3, the RECONNECT trials. 1,247 patients.
- 03Pooled safety analysis of bremelanotide across 43 studies and approximately 3,500 subjects, 2022. Safety review. Nausea 40.0 percent against 1.3 percent, flushing 20.3 percent, headache 11.3 percent.
- 04Published work on melanocortin agonists and cardiovascular response, including blood pressure and heart rate effects of MC4R activation. Pharmacology literature. Volume and page numbers not in hand; the FDA label carries the same contraindication.
- 05Earlier subcutaneous bremelanotide studies in men with erectile dysfunction at 4 and 6 milligram doses. Human studies, objectively measured erectile response. Program not carried through to approval.
- 06Imperial College London brain imaging work on kisspeptin and responses to sexual and emotional stimuli. Human imaging study, not an outcome trial.
- 07Dhillo WS, et al. Kisspeptin-54 stimulates the hypothalamic-pituitary-gonadal axis in human males. J Clin Endocrinol Metab. 2005. Human study, first published human work on kisspeptin.
- 08Jayasena CN, et al. Subcutaneous injection of kisspeptin-54 acutely stimulates gonadotropin secretion in women with hypothalamic amenorrhea, but chronic administration causes tachyphylaxis. J Clin Endocrinol Metab. 2009;94(11):4315-4323. Randomized human trial, 10 patients. LH response fell from 24.0 to 2.5 IU/L over two weeks of twice daily dosing.
- 09Jayasena CN, et al. Twice weekly administration of kisspeptin-54 for eight weeks in women with hypothalamic amenorrhea. Clin Pharmacol Ther. 2010. Human study. Reduced desensitization, menstruation not restored.
- 10George JT, et al. Kisspeptin-10 stimulation of gonadotropin secretion in men: dose response. 2011. Human study. Higher dose produced a smaller LH rise than lower doses.
- 11Janvier S, Cheyns K, Canfyn M, et al. Impurity profiling of the most frequently encountered falsified polypeptide drugs. Talanta. 2018;188:795-807. Peer-reviewed analytical study. Purity 5 to 75 percent, plus arsenic and lead.
- 12NBC Washington. Lab finds problems in 30% of peptide vials tested. December 2024. News report of commercial laboratory testing, not peer reviewed.