Kisspeptin

A hormone the body already makes, and the switch that turns the reproductive system on at puberty. The KISS1 gene produces a 54-amino-acid peptide called kisspeptin-54, or metastin. Kisspeptin-10 is simply its last ten amino acids — YNWNSFGLRF, positions 45 to 54 of the longer chain — which is the shortest piece that still switches the receptor on. The chain printed here is kisspeptin-54, the form used in almost every trial a reader is likely to have heard of. The form sold online and compounded by clinics is kisspeptin-10. Both end in an amide, a chemical cap on the tail of the chain that the one-letter code cannot show, so it is stated here in words instead: the final phenylalanine is amidated in both forms, which UniProt records for the natural peptide and the US regulator writes out as H-Tyr-Asn-Trp-Asn-Ser-Phe-Gly-Leu-Arg-Phe-NH2 for kisspeptin-10.

Sold as

In published studies, into a vein as a drip, or under the skin as a single injection. The short physiology and brain-scan studies used a drip; the IVF programme and the courses that ran for days or weeks used injections under the skin. One 2025 study tested a nasal spray. Sold online and by clinics as an injection or a lozenge.

Legal status in the EU

Not approved as a medicine in the EU, the UK, the United States or anywhere else, for any use. The US regulator states there is no approved product in any country containing kisspeptin-10, and that it appears in neither the European nor the Japanese pharmacopoeia. On 29 October 2024 the FDA's Pharmacy Compounding Advisory Committee voted 0 in favour and 11 against adding kisspeptin-10 to the list of substances US pharmacies may compound, agreeing unanimously that it should not be included because of a lack of convincing safety and efficacy data; the nominated use had been treatment of secondary hypogonadism in men. Kisspeptin-10 now sits in Category 2 of the FDA's list of nominated bulk substances, "substances that raise significant safety risks", as of the list updated 14 May 2026. In Sweden, selling or advertising an unapproved medicine to the public is prohibited under the Medicinal Products Act (2015:315), and nothing checks what is in a vial bought online.

It binds a receptor called GPR54 (also written KISS1R) on a small group of nerve cells in the hypothalamus, the part of the brain that runs hormones. Those cells release a pulse of GnRH, the messenger that tells the pituitary gland to put out LH and FSH, and those two travel to the testicles or the ovaries. Because it acts at the very top of that chain, it can only do anything if the hypothalamus and pituitary gland underneath it are working — which is why it mostly produced no response at all in men whose hypothalamus does not release GnRH properly, the group it is most often compounded for. Given continuously rather than in pulses, the same receptor is worn down and the response fades, an effect a drug company tried to use deliberately to shut the system down in prostate cancer.

Part of the bodyWhat happensHow it is knownKind of evidence

The switch in the brain that starts the reproductive chain

Kisspeptin lands on a receiver on a small group of nerve cells in the hypothalamus, the part of the brain that runs hormones. Those cells release a pulse of GnRH, the messenger that tells the pituitary gland to put out two hormones called LH and FSH. LH and FSH then travel to the testicles or the ovaries. The whole sequence starts within minutes of an injection and is the most reliably reproduced thing kisspeptin does. In six healthy men given a 90-minute drip, average LH was 10.8 units per litre against 4.2 on a saline drip.

Measured in several hundred people. For the 10-amino-acid form alone the US regulator catalogued 24 published human studies running from 2011 to 2022, in healthy men, healthy women, women after the menopause, children, adolescents with delayed puberty and patients with several reproductive conditions; the 54-amino-acid form has its own separate series of studies going back to 2005. Two groups did most of it: Imperial College London, using the 54-amino-acid form, and Massachusetts General Hospital, using the 10-amino-acid form.

Measured in people

Source [01]Source [09]

The ovaries, and the release of an egg

In fertility treatment, one injection has to tell the ovaries to finish ripening the eggs before they are collected. Kisspeptin-54 does this. A single injection under the skin produced its own surge of LH, and eggs matured at every amount tested. It appears to carry a lower risk of the dangerous over-response that the standard trigger can cause, because the surge it produces is shorter. That last point has never been tested against the standard trigger in the same study, so it remains a comparison nobody has actually run.

Measured in 175 women having IVF at one London hospital between 2012 and 2016, in a phase 2 programme run by Imperial College London. No woman in any group received the standard trigger injection for comparison. Nobody outside that hospital has repeated it.

Measured in people

Source [05]Source [10]Source [11]

Sexual arousal, in the brain

In brain scans, kisspeptin changes activity in the areas that handle sexual images and attraction. In men with long-standing low sexual desire it also increased the physical erection response to a sexual video and how happy men said they felt about sex. What it did not do, in either the men's trial or the women's, was move the overall score on the questionnaire that measures sexual desire. Every one of these measurements was taken during a single 75-minute drip in a scanner. Nobody has been given kisspeptin and then asked, weeks later, whether their sex life changed.

Measured in three randomised, placebo-controlled crossover trials, all at one centre in London: 29 healthy men, then 32 women with low sexual desire, then 32 men with low sexual desire. Crossover means each person had both the drug and the dummy on separate days and acted as their own comparison. No other group has repeated any of it.

Measured in people

Source [08]Source [12]Source [13]

Appetite and how much people eat

Nothing measurable happens. Clinics sell kisspeptin as a weight-loss injection; the studies that looked found no effect. In 17 women with overweight or obesity, the meal eaten after a kisspeptin drip came to 6.8 kilocalories per kilogram of body weight against 6.2 after the dummy drip, a difference well within chance. Self-rated hunger was no different either. In 15 healthy men, the calories eaten were 845 on kisspeptin and 834 on the dummy. In 27 healthy men, brain responses to pictures of food did not change.

Measured in three separate crossover studies in people, each comparing kisspeptin with a dummy drip in the same participants: 17 women with overweight or obesity, 15 healthy men, and 27 healthy men in a scanner. No study has weighed anyone before and after a course of kisspeptin.

Measured in people

Source [14]Source [15]Source [16]

Blood pressure and heart rate

Neither moves. This has been checked deliberately, because kisspeptin narrows blood vessels in laboratory tissue and because blood levels of it rise enormously in pregnancy, where blood pressure problems are common. Giving it by drip to healthy men and by injection to healthy women changed neither blood pressure nor heart rate. A later study of 95 people found the same.

Measured in healthy men and women given kisspeptin-54 at several different amounts against a dummy, with blood pressure and heart rate recorded throughout; and again in 95 people in a randomised placebo-controlled crossover study published in 2025.

Measured in people

Source [18]Source [19]

Mood and anxiety

In mice, kisspeptin acting in one part of the brain makes them more anxious, which raised a real worry about giving it to people. It was tested. In 95 people, anxiety scores after kisspeptin were no different from anxiety scores after the dummy drip, while LH rose sharply — so the dose was doing something, just not that. Stress hormone levels did not change either.

Measured in 95 people, 63 men and 32 women, in a double-blind randomised placebo-controlled crossover study; each person had both the drug and the dummy. This pools participants from several of the same group's earlier trials.

Measured in people

Source [19]

Testicles and testosterone in men

This is what it is sold for, and it is where the evidence pulls apart. A single dose does raise testosterone a little: in six healthy men, average testosterone over three hours was 24.9 nanomoles per litre against 21.7 on saline. In four men with type 2 diabetes and low testosterone given an 11-hour drip, testosterone rose from 8.5 to 11.4 nanomoles per litre over the drip, each man measured against his own starting level — that study had no dummy-drip group. But in men who actually have the condition kisspeptin-10 is compounded for — a hypothalamus that does not release GnRH properly — kisspeptin-10 mostly produced no LH response at all, while the same men responded normally to GnRH itself. And when a close copy of kisspeptin-10 was given daily or weekly for six weeks against a dummy injection, testosterone did not rise more than on the dummy.

Measured in small studies in people: 6 healthy men on a drip against saline; 4 men with diabetes against their own starting levels; four studies in patients with hypothalamic hypogonadism, three of them at Massachusetts General Hospital and one in France, all but the French one giving GnRH as a check that the pituitary gland could respond; and one randomised placebo-controlled trial of the kisspeptin analogue TAK-448 in 17 middle-aged and older men with low testosterone, terminated by the sponsor for missing its primary endpoint.

Studies in people disagree

Source [01]Source [04]Source [09]

Insulin and blood sugar

In one small study, kisspeptin nudged the pancreas to release a little more insulin after a sugar load — average insulin was 4.1 microunits per millilitre higher than on the dummy drip. Blood sugar itself was the same on both days. Nobody has followed this up in people with diabetes or over any length of time, and two planned follow-up studies were withdrawn before enrolling anyone.

Measured in 15 healthy men in a randomised crossover study, each man having both kisspeptin and a dummy drip on separate days. One 16-person follow-up at Massachusetts General Hospital has posted results; two further studies were registered and then withdrawn with nobody enrolled.

One small study

Source [15]Source [17]

The walls of the arteries, in mice

Mice bred to develop clogged arteries were given kisspeptin-10 continuously for four weeks by an implanted pump. The furring-up of the main artery got worse, with more immune cells piling into the vessel wall. Two amounts were infused; only the higher of them significantly changed the lesions. Blocking the kisspeptin receiver stopped it, which means it was the kisspeptin doing it. Whether any of this applies to a person is unknown; nobody has looked.

Seen in mice genetically bred to develop atherosclerosis, given kisspeptin-10 by an implanted pump for four weeks at two doses, against mice given the carrier liquid. Never looked for in a person, at any dose, over any period.

Only seen in animals

Source [01]Source [20]

The only randomised, placebo-controlled course lasting weeks failed. Takeda gave TAK-448, a modified copy of kisspeptin-10, to 17 middle-aged and older men with low testosterone for six weeks (NCT02381288): average testosterone rose 14.3% on the dummy injection against 7.1%, 10.6% and 15.8% on the three drug doses, and the sponsor terminated the trial stating it did not meet its primary endpoint. A second trial of the same compound in 15 men (NCT02369796) was terminated for the same reason. Everything else is small and short. Kisspeptin reliably raises LH and FSH within minutes, which is uncontested and was first shown in 6 healthy men in 2005 (LH 10.8 vs 4.2 units per litre against saline). The phase 2 IVF programme at Imperial College London (NCT01667406, 175 women, completed October 2016) used kisspeptin-54 to trigger egg maturation and babies were born, but no group in it ever received the standard trigger injection for comparison, so it establishes nothing about whether kisspeptin is better, worse or equal to what clinics already use; the one randomised comparison inside it was one dose against two, where two came out ahead (22 of 31 vs 14 of 31 reaching the target egg yield). In two crossover trials in people with long-standing low sexual desire (32 women, 32 men), brain-scan responses shifted against placebo and the men's erection response rose, while the overall sexual desire scores did not move in either. Almost all of this comes from one group in London and none of it has been independently repeated. A second, independent group at Massachusetts General Hospital has worked with kisspeptin-10 for two decades and found that patients whose hypothalamus does not release GnRH properly generally showed no LH response to it at all, while responding normally to GnRH. Sequence re-derived from UniProt Q15726, which records the C-terminal phenylalanine amide.

Fast, and short. Kisspeptin-54 clears from the blood with a half-life of about 28 minutes in people — the half-life is the time it takes for half of it to disappear. LH starts climbing within minutes of an injection and the surge produced by the IVF trigger dose is over in well under a day, which is the point of using it there. Kisspeptin-10 is far shorter still, with a half-life of roughly four minutes; in mice its LH response lasted about ten minutes against more than two hours for kisspeptin-54, and repeated injections of kisspeptin-10 could not reproduce what one injection of kisspeptin-54 did. The longest anyone has been given kisspeptin continuously in a published study is 24 hours. The longest repeated course is twice a week for eight weeks. Nothing is known about what happens after that, because nobody has gone further.

What was measuredWhat happenedIn whomHow it is known

Testosterone after six weeks of treatment — the one controlled course lasting weeks

Average testosterone rose 14.3 per cent on the dummy injection, and 7.1, 10.6 and 15.8 per cent on the three drug doses. Only the top dose came out above the dummy at all, by 1.5 percentage points, against a scatter in the measurements many times that size. The sponsor terminated the trial, stating that it did not meet its primary endpoint. A second trial of the same compound, in 15 men whose hypothalamus does not release GnRH properly, was terminated for the same reason. Both trials tested TAK-448, a modified copy of kisspeptin-10 rather than kisspeptin itself, which is the closest anyone has come to testing the claim that kisspeptin raises testosterone.

17 middle-aged and older men with low testosterone, injected under the skin daily, twice weekly or once weekly for six weeks, against a matching dummy injection; sponsored by Takeda, 2015 to 2016.

Measured in people

Source [04]Source [21]

Whether a second injection of kisspeptin-54 improves the egg harvest in IVF

22 of 31 women given a second injection ten hours after the first reached the target egg yield, against 14 of 31 given salt water as the second injection — a difference of 26 percentage points, which the authors report as just inside statistical significance. Live births followed at 12 of 31 against 6 of 31, but the trial was not designed to measure births and that difference could easily be chance. One woman in each group developed the over-response the treatment is meant to avoid, one moderate and one mild.

62 women at high risk of ovarian hyperstimulation syndrome having IVF at one London hospital, recruited between August 2015 and May 2016; both groups received kisspeptin-54, so this compares one dose with two, not kisspeptin with standard care.

Measured in people

Source [22]

Erection response and reported feelings in men with low sexual desire

The physical erection response to a sexual video was up to 56 per cent greater on kisspeptin than on the dummy drip — a mean difference of 0.28 units, only just clear of no difference at all — and men reported feeling happier about sex by 0.63 points on the scale used. Brain activity in the network that handles sexual images also shifted. What did not change: the overall score on the questionnaire that measures sexual desire, general mood, anxiety, and attention to things that were not sexual. Testosterone did not change during the 75 minutes either.

32 men with long-standing low sexual desire who completed both visits, out of 37 randomised; each man had a 75-minute drip of kisspeptin-54 and a matching dummy drip on separate days at least a week apart.

Measured in people

Source [08]

Brain activity and reported feelings in women with low sexual desire

Brain activity while watching erotic videos and rating faces shifted against the dummy drip in several regions. On the questionnaires, the only item that moved was feeling "sexy", up by 0.5 points, and the authors label that an exploratory finding rather than a planned one. The overall sexual desire scores did not change. Anxiety did not change. Oestradiol, progesterone and testosterone did not change.

32 premenopausal women with low sexual desire who completed both visits, out of 40 randomised; each woman had a 75-minute drip of kisspeptin-54 and a matching dummy drip at least a month apart, in the first week of her cycle.

Measured in people

Source [12]

How much people eat after a kisspeptin drip

6.8 kilocalories per kilogram of body weight on kisspeptin against 6.2 on the dummy drip, a difference the study reports as not significant. Self-rated hunger was no different, and neither was heart rate or blood pressure. In a separate study in 15 healthy men the meal came to 845 kilocalories on kisspeptin and 834 on the dummy.

17 women with overweight or obesity, average age 49 and average body mass index 34, each attending two identical visits differing only in what was in the drip; and separately 15 healthy men.

Measured in people

Source [14]Source [15]

Whether kisspeptin-10 works in men whose hypothalamus does not release GnRH properly

Mostly it did not. Across the four studies, patients with this condition generally produced no LH response to kisspeptin-10, while the same patients responded normally to GnRH given as a check that their pituitary gland was working. There were exceptions. In the French study, a 12-hour drip in four patients whose condition came from a fault in a different signalling pathway did restore LH pulses. And of six men whose condition had spontaneously reversed, the four who had got their natural hormone pulses back responded, while the two who had relapsed did not. In a further study, seven patients given kisspeptin-10 while on sex-hormone replacement, five of them also off it, produced no response in either state, though all of them responded to GnRH.

25 men and 4 women with hypothalamic hypogonadism across four studies, each given kisspeptin-10 into a vein. Three of the four were run at Massachusetts General Hospital and one in France; all but the French one gave GnRH as a positive control. The regulator's own reading is that no conclusion about effectiveness can be drawn from studies this small, which were designed to probe the pathway rather than to treat anyone.

Measured in people

Source [01]

Anxiety

No difference between kisspeptin and the dummy drip on the anxiety questionnaire. LH rose sharply on kisspeptin in the same people, which shows the dose was biologically active. Stress hormone levels, blood pressure and heart rate were also unchanged. This matters because kisspeptin makes mice more anxious, and the human answer came out the other way.

95 people, 63 men and 32 women, average age 31, each receiving a 75-minute drip of kisspeptin-54 and a matching dummy drip on separate days.

Measured in people

Source [19]

LH, the hormone that tells the testicles or ovaries to work

Average LH over 90 minutes was 10.8 units per litre on kisspeptin-54 against 4.2 units per litre on a saline drip. FSH was 3.9 against 3.2 and testosterone over three hours was 24.9 against 21.7 nanomoles per litre. Each man had both the drug and the saline on separate days, in a random order, without knowing which was which.

6 healthy men, 90-minute drip, in the first study ever to give kisspeptin to a person.

One small study

Source [09]

Whether a nasal spray works instead of a needle

It does, at least for the hormone signal. At the amount common to all three groups, LH ran 3.1 units per litre higher than on the dummy spray in healthy men, 1.0 higher in healthy women, and 4.3 higher in women whose hypothalamus had stopped driving the cycle. Each of those is the gap against the dummy spray, not the rise from where the person started — the paper reports both, and the rises from baseline are 4.4, 1.4 and 4.4 units per litre. Nobody reported any side effect of any severity. This was a single spray on a single day; whether repeated use keeps working is unstudied.

12 healthy men, 12 healthy women and 10 women with hypothalamic amenorrhoea, each attending visits with kisspeptin-54 spray and with a dummy spray.

One small study

Source [23]

The published trials repeatedly report no side effects and no adverse events, but that is a weaker statement than it looks: nearly every exposure was a single dose or a drip of at most 24 hours, in healthy volunteers, in a hospital, and 14 of the 24 published kisspeptin-10 studies the FDA catalogued have "Not reported" in the safety column. There is no long-term human safety information of any kind, and nobody has checked whether the immune system makes antibodies against it — a risk the regulator raised specifically, noting that for the material pharmacies would use it had only a total impurity limit and nothing on the nature and level of the individual impurities. The response fades if it is given too often: twice-daily kisspeptin-54 did this in women whose periods had stopped. In a four-week animal study, kisspeptin-10 worsened arterial plaque in mice bred to develop clogged arteries at the higher of the two doses infused; the lower dose did not significantly change the lesions. One report exists in the FDA's side-effect database, from a 17-year-old given a compounded kisspeptin-10 injection for six weeks; he gained weight and his oestrone rose, neither of which was the intended effect. Against that, the only formal repeat-dose toxicity study in the same regulatory review gave Beagle dogs daily kisspeptin-10 into a vein for 14 days at up to 1,000 micrograms per kilogram and found no drug-related effect on behaviour, weight, food intake, blood tests, tissue samples, urine, heart tracings or breathing.

EffectWhat it feels likeHow often

Nothing at all, in study after study — and that is a weaker statement than it looks

Almost every one of these exposures was a single dose or a drip lasting a day at most, in healthy volunteers, in a hospital, with a doctor present. That is the setting least likely to turn up a problem and the shortest period over which one could appear. Reporting no side effects after 75 minutes is not the same kind of statement as reporting no side effects after a year.

The published trials repeatedly report no side effects and no adverse events. The important caveat is in the US regulator's own table: of the 24 published human studies of kisspeptin-10 it catalogued, 14 have "Not reported" in the safety column, because safety was not something those studies set out to record.

Source [01]Source [08]

It stops working if given too often

The receiver that kisspeptin acts on gets worn down by constant stimulation, and the hormone response fades — the technical word is tachyphylaxis. The US regulator reports the same effect for kisspeptin-10 in animal work, where a continuous high-dose drip in monkeys raised LH for about three hours before it fell back to the starting level with the drip still running. Nobody has established what schedule avoids this in a person, which is one reason no dosing instruction here would be honest.

Seen when kisspeptin-54 was injected twice a day in women whose periods had stopped. The same twice-daily schedule did not do it in healthy women in the first half of the cycle. Twice a week for eight weeks caused only partial fading, and still left reproductive hormones higher than on salt water at the end of the eight weeks.

Source [01]Source [24]Source [25]

The one report from someone who bought it, rather than volunteered for a study

A 17-year-old boy with a hypothalamus that does not release GnRH properly was given a compounded kisspeptin-10 injection, 100 micrograms a day under the skin for six weeks, to try to raise his testosterone. He gained weight and one of his oestrogens went up. Neither was the intended effect. The regulator notes the report is thin: no past medical history, no other medicines listed, no records. One report is not a safety signal, and it is not reassurance either — reporting is voluntary and almost nobody files a form about something bought from a clinic.

One report, in the US regulator's public side-effect database, as of its data update of 28 April 2026. A search of the separate database for supplements and cosmetics returned none.

Source [01]Source [26]

Whether the immune system learns to attack it

A ten-amino-acid chain injected under the skin is long enough for the immune system to notice, and the risk goes up if the product has clumped or carries manufacturing impurities. The US regulator raised exactly this, noting that the nomination gave a total impurity limit but no information on the nature and level of the individual impurities in the material pharmacies would use, and that one possible consequence of an immune response is antibodies that neutralise the body's own kisspeptin as well as the injected kind. Nothing here is a finding — it is a question nobody has answered.

Not measured. No study has ever looked, in any person, for either form.

Source [01]

Anything that takes longer than a few days to appear

There is no long-term human safety record of any kind. The regulator's reviewers also noted that the animal toxicity studies available to them were too limited in scope and duration to inform safety for any clinical use.

Not measured, for either form. The longest anyone has been given kisspeptin continuously in a published study is 24 hours. The longest repeated course is twice a week for eight weeks, in a small group of women.

Source [01]

These are the amounts the studies below gave their participants, and they are here as facts about those studies. They are not a recommendation, not a starting point and not a range to pick from. What a person should take, if anything, is a question for a doctor who knows them.

Dhillo and colleagues 2005 — the first study ever to give kisspeptin to a person, in 6 healthy men, against a saline drip

Kisspeptin-54 by drip into a vein, 4 picomoles per kilogram of body weight per minute.

90 minutes, with blood sampled for three hours.

Source [09]

The Imperial College London IVF programme (NCT01667406) — using kisspeptin-54 as the injection that ripens the eggs before collection, in 175 women across several groups between 2012 and 2016

A single injection under the skin, in nanomoles per kilogram of body weight: 1.6, 3.2, 6.4, 9.6 or 12.8 depending on the group. One later group received 9.6 and then a second injection of 9.6 ten hours afterwards, against a group whose second injection was salt water.

A single injection 36 hours before the eggs were collected, or two injections ten hours apart. No group received the standard trigger injection for comparison.

Source [10]Source [11]Source [22]

The low sexual desire trials (ISRCTN17271094) — 32 women and 32 men with long-standing low sexual desire, each compared with a matching dummy drip

Kisspeptin-54 by drip into a vein, 1 nanomole per kilogram of body weight per hour.

75 minutes, on two separate visits at least a week apart for the men and at least a month apart for the women.

Source [08]Source [12]

The published human studies of kisspeptin-10, the form that is actually sold — catalogued by the US regulator in October 2024

Almost all into a vein: single injections of 0.01 to 13 micrograms per kilogram of body weight, or drips at rates from 0.13 to 12.5 micrograms per kilogram per hour, with one 30-minute study running far faster than that. The regulator found exactly one study that gave kisspeptin-10 under the skin, a single injection in about 35 healthy women, and that study reported no safety outcomes. It found no study at all that gave it into a muscle.

Single doses on one or two days in most studies. The longest drip was 24 hours, in eight women past the menopause; the longest series of injections was ten, one an hour, on a single day.

Source [01]

Takeda's TAK-448 — a modified copy of kisspeptin-10, given for six weeks against a dummy injection in 17 middle-aged and older men with low testosterone

Under the skin: 0.1 microgram daily, 0.3 micrograms twice weekly, or 1.0 microgram once weekly, against a matching dummy injection.

Six weeks. The trial was terminated by the sponsor for missing its primary endpoint, and the results are posted on the registry.

Source [04]

What people report

• Whether it does anything for sexual desire outside a hospital scanner: both low-desire trials measured a single 75-minute drip and neither followed anyone up.
• Whether it improves the chance of a live birth compared with the standard IVF trigger — no study has ever put the two side by side.
• Whether it raises testosterone over weeks: the only placebo-controlled course lasting weeks used a close copy and was stopped for missing its primary endpoint.
• Whether it does anything at all for the men it is most often compounded for — those with a hypothalamus that does not release GnRH properly mostly showed no response.
• Whether the form actually sold, kisspeptin-10, does anything when injected under the skin: the regulator found one such study, in about 35 healthy women, which reported no safety outcomes and no clinical result.
• Whether kisspeptin-10 does anything when injected into a muscle, which is one of the two routes it was nominated for: no human study of that route exists.
• Whether it affects body weight or body fat in a person, despite being sold as a weight-loss injection.
• Whether the immune system makes antibodies against it over time, and whether those antibodies would also neutralise the body's own kisspeptin.
• What schedule avoids the fading response, which appears when it is given too often and which no human study has mapped.
• What happens beyond 24 hours of continuous use, which is as long as anyone has ever been given it in one stretch.
• Whether the worsening of furred arteries seen in mice happens in people, or only in those already prone to it.
• What is in the vials sold online: no published chemical analysis of a purchased product exists, and for the material pharmacies would use the regulator had only a total impurity limit, with nothing on the individual impurities.
• Whether any of the London findings hold up elsewhere: the fertility work, the low-desire trials and the nasal spray all come from one group at one hospital, and none has been repeated by anyone else.
• Whether the nasal spray keeps working with repeated use, having been tested once, on one day, in 34 people.
• What it does in children and adolescents beyond single research injections given in hospital, and what it does in pregnancy or breastfeeding.
• Whether it is safe alongside anything else, since no published study has given it with another drug outside a research protocol.

Does kisspeptin work for libido?

It does something measurable, but not the thing most people mean. In two trials from one London hospital — 32 women and 32 men, each with long-standing low sexual desire — a 75-minute kisspeptin drip changed brain activity while people watched sexual material, increased the erection response in the men and made them report feeling happier about sex, and made the women rate themselves as feeling slightly more "sexy". In both trials the overall score on the questionnaire that actually measures sexual desire did not change. Everything was measured during a single visit in a hospital scanner; nobody has been given kisspeptin and then asked weeks later whether their sex life was different.

Source [08]Source [12]

Does kisspeptin help fertility or IVF?

In IVF it has been used as the injection that ripens the eggs before they are collected, and it works for that: 175 women at one London hospital received it between 2012 and 2016, eggs matured, and babies were born. But not one of those women was given the standard trigger injection for comparison, so there is no published evidence that kisspeptin does the job better, worse or as well as what clinics already use. The only proper comparison inside the whole programme was between one dose and two, where two came out ahead. It is not approved for fertility treatment anywhere, and it is not what is being sold online under the name kisspeptin.

Source [05]Source [10]Source [22]

Does kisspeptin raise testosterone?

A single dose raises it slightly and briefly — in six healthy men, 24.9 nanomoles per litre against 21.7 on saline over three hours. Over weeks it has not been shown to. The only randomised, placebo-controlled course lasting weeks used TAK-448, a modified copy of kisspeptin-10, in 17 men with low testosterone: after six weeks, average testosterone was up 14.3 per cent on the dummy injection and 7.1, 10.6 and 15.8 per cent on the three drug doses. The sponsor stopped the trial because it missed its primary endpoint, and stopped a second one in men with hypothalamic hypogonadism for the same reason.

Source [01]Source [04]Source [09]

Is kisspeptin legal, and can you buy it?

It is not an approved medicine in the EU, the UK, the United States or anywhere else, so there is no legal way to be prescribed it as a treatment. It is sold anyway, as a research chemical online and as a compounded injection or lozenge by some clinics. In the United States the regulator has now closed that door: on 29 October 2024 its Pharmacy Compounding Advisory Committee voted 11 to nothing that kisspeptin-10 should not go on the list of substances pharmacies may compound, and kisspeptin-10 now sits in the category of bulk substances judged to raise significant safety risks. In Sweden and the rest of the EU, selling an unapproved medicine to consumers is not permitted, and nothing checks what is in a vial bought online.

Source [01]Source [02]Source [03]

What are the side effects of kisspeptin?

In the published trials, almost none are reported — participants repeatedly finish a drip or an injection with nothing to say, and blood pressure, heart rate and anxiety do not move. The honest reading is that this is a weak statement, not a strong one: nearly every exposure was a single dose in a hospital, and the US regulator's own catalogue shows that 14 of the 24 published studies did not record safety at all. The one thing known to go wrong is that it stops working when given too often. There is no long-term human safety data of any kind, nobody has checked whether the immune system reacts to it, and a four-week animal study found it worsening furring of the arteries in mice bred to develop it.

Source [01]Source [19]

What is the difference between kisspeptin-10 and kisspeptin-54?

They are the same chain cut to different lengths. The body makes a 54-amino-acid piece, also called metastin; kisspeptin-10 is just the last ten amino acids of it, which is the shortest stretch that still switches the receiver on. The difference matters in practice: in people, half of a dose of kisspeptin-54 has cleared the blood in about 28 minutes against under 4 minutes for kisspeptin-10, and in mice only the 54 version reached the nerve cells behind the brain's protective barrier, so repeated injections of kisspeptin-10 could not reproduce what one injection of kisspeptin-54 did. Nearly all the trial evidence people search for — fertility, sexual desire — used kisspeptin-54. Nearly everything sold is kisspeptin-10.

Source [01]Source [06]Source [09]Source [27]

Kisspeptin vs hCG — is it a replacement?

Some clinics have marketed it that way, and the US regulator quotes one website offering kisspeptin-10 as an alternative to hCG. No study has ever compared the two, in fertility treatment or in men. hCG is an approved medicine with decades of use and a published product information sheet; kisspeptin is approved nowhere and its longest controlled test in men failed. The two also work at different points in the chain: hCG acts directly on the testicles or ovaries, while kisspeptin acts on the brain and therefore needs the hypothalamus and pituitary gland underneath it to be working — which is exactly why it produced no response in most of the men with hypothalamic hypogonadism who were given it.

Source [01]

Does kisspeptin cause weight loss?

Not in anything that has been measured. Clinics sell it as a weight-loss injection — the US regulator quotes one claiming it breaks down stored fat — and three separate studies looked for an effect on eating and found none. In 17 women with overweight or obesity the meal after a kisspeptin drip came to 6.8 kilocalories per kilogram against 6.2 after the dummy, with no difference in hunger; in 15 healthy men it was 845 kilocalories against 834; and in 27 healthy men, brain responses to pictures of food did not shift. Nobody has weighed a person before and after a course of it.

Source [01]Source [14]Source [15]

Is kisspeptin banned in sport?

Yes, at all times, in and out of competition. The 2026 Prohibited List names "kisspeptin and its agonist analogues" in section S2.2.1, among testosterone-stimulating peptides in males, alongside hCG, LH and the GnRH agonists. Everything in section S2 is prohibited both in and out of competition. The heading limits that particular entry to males, which is how the list treats the other testosterone-stimulating peptides in the same bullet list.

Source [07]

Each letter represents one amino acid.

1. [01]FDA briefing document for kisspeptin-10, Pharmacy Compounding Advisory Committee, 29 October 2024 — chemistry, the 24 catalogued human exposures, the IHH studies, the FAERS case and the safety conclusions (2024)
2. [02]Summary minutes, FDA Pharmacy Compounding Advisory Committee, 29 October 2024 — vote on kisspeptin-10: Yes 0, No 11, Abstain 0 (2024)
3. [03]FDA: Bulk Drug Substances Nominated for Use in Compounding Under Section 503A, updated 14 May 2026 — kisspeptin-10 listed under Category 2, substances that raise significant safety risks (2026)
4. [04]Effects of TAK-448 in Middle-aged and Older Men With Low Testosterone (NCT02381288, phase 2, 17 men, Takeda, terminated because the study did not meet the primary endpoint, results posted) (2016)
5. [05]The Use of the Hormone Kisspeptin in IVF Treatment (NCT01667406, phase 2, 175 women, Imperial College London, completed 11 October 2016, results posted) (2016)
6. [06]UniProt Q15726 (KISS1_HUMAN) — metastin at residues 68–121, kisspeptin-10 at 112–121, and MOD_RES 121 recorded as phenylalanine amide
7. [07]WADA: World Anti-Doping Code International Standard – Prohibited List 2026, section S2.2.1, testosterone-stimulating peptides in males, naming kisspeptin and its agonist analogues; in force 1 January 2026 (2026)
8. [08]Mills EG and colleagues, effects of kisspeptin on sexual brain processing and penile tumescence in men with hypoactive sexual desire disorder (JAMA Netw Open 2023;6(2):e2254313; 32 of 37 men completed, crossover against placebo) (2023)
9. [09]Dhillo WS and colleagues, kisspeptin-54 stimulates the hypothalamic-pituitary gonadal axis in human males (J Clin Endocrinol Metab 2005;90(12):6609-15; 6 men, crossover against saline) (2005)
10. [10]Jayasena CN, Abbara A and colleagues, kisspeptin-54 triggers egg maturation in women undergoing in vitro fertilization (J Clin Invest 2014;124(8):3667-77; 53 women, no comparator trigger arm) (2014)
11. [11]Abbara A and colleagues, efficacy of kisspeptin-54 to trigger oocyte maturation in women at high risk of OHSS (J Clin Endocrinol Metab 2015;100(9):3322-31; 60 women, open-label, no comparator trigger arm) (2015)
12. [12]Thurston L and colleagues, effects of kisspeptin administration in women with hypoactive sexual desire disorder (JAMA Netw Open 2022;5(10):e2236131; 32 women, crossover against placebo) (2022)
13. [13]Comninos AN and colleagues, kisspeptin modulates sexual and emotional brain processing in humans (J Clin Invest 2017;127(2):709-719; 29 healthy men) (2017)
14. [14]Izzi-Engbeaya C and colleagues, the effects of kisspeptin on food intake in women with overweight or obesity (Diabetes Obes Metab 2024;26(1):125-134; 17 women, crossover against vehicle) (2024)
15. [15]Izzi-Engbeaya C and colleagues, the effects of kisspeptin on beta-cell function, serum metabolites and appetite in humans (Diabetes Obes Metab 2018;20(12):2800-2810; 15 healthy men, crossover against vehicle) (2018)
16. [16]Yang L and colleagues, the effects of kisspeptin on brain response to food images and psychometric parameters of appetite in healthy men (J Clin Endocrinol Metab 2021;106(4):e1837-e1848; 27 men, crossover against vehicle) (2021)
17. [17]Evaluation of Kisspeptin Glucose-Stimulated Insulin Secretion With Oral Glucose (NCT04958109, phase 1, 16 participants, Massachusetts General Hospital, completed, results posted) (2023)
18. [18]Nijher GMK and colleagues, the effects of kisspeptin-54 on blood pressure in humans and plasma kisspeptin concentrations in hypertensive diseases of pregnancy (Br J Clin Pharmacol 2010;70(5):674-81) (2010)
19. [19]Mills EG and colleagues, kisspeptin administration stimulates reproductive hormones but does not affect anxiety in humans (J Clin Endocrinol Metab 2025; 95 people, crossover against placebo) (2025)
20. [20]Sato K and colleagues, potent vasoconstrictor kisspeptin-10 induces atherosclerotic plaque progression and instability: reversal by its receptor GPR54 antagonist (J Am Heart Assoc 2017;6(4):e005790) (2017)
21. [21]A Phase 2a Pharmacodynamic Study of TAK-448 in Participants With Hypogonadotropic Hypogonadism (NCT02369796, 15 men, terminated: 'the study did not achieve the primary efficacy objective') (2015)
22. [22]Abbara A and colleagues, a second dose of kisspeptin-54 improves oocyte maturation in women at high risk of ovarian hyperstimulation syndrome: a phase 2 randomized controlled trial (Hum Reprod 2017;32(9):1915-1924) (2017)
23. [23]Mills EG, Silva AS, Delli V and colleagues, intranasal kisspeptin administration rapidly stimulates gonadotropin release in humans (eBioMedicine 2025) (2025)
24. [24]Jayasena CN and colleagues, twice-weekly administration of kisspeptin-54 for 8 weeks stimulates release of reproductive hormones in women with hypothalamic amenorrhea (Clin Pharmacol Ther 2010) (2010)
25. [25]Abbara A, Dhillo WS and colleagues, kisspeptin receptor agonist has therapeutic potential for female reproductive disorders (J Clin Invest 2020) — twice-daily kisspeptin-54 induced tachyphylaxis in women with hypothalamic amenorrhoea (2020)
26. [26]Side-effect reports naming kisspeptin in the FDA adverse event database (openFDA query, one report, data current to 28 April 2026)
27. [27]d'Anglemont de Tassigny X, Jayasena C, Murphy KG, Dhillo WS, Colledge WH, mechanistic insights into the more potent effect of KP-54 compared to KP-10 in vivo (PLoS One 2017;12(5):e0176821) (2017)