The peptide
What is kisspeptin? The reproductive neuropeptide, explained.
The KISS1 gene product, its receptor, its two main isoforms, and the one distinction that explains everything: it acts upstream of GnRH.
Start here
The kisspeptin peptide is a small chain of amino acids that the body makes from the KISS1 gene, and its job is to be the starter button for the reproductive hormone system. It works by fitting into a receptor called KISS1R (older name GPR54) on certain brain cells, switching them on. Those cells release GnRH, which sets off the rest of the chain down to the sex hormones.
The most important thing to understand about kisspeptin is what it is not. It is not a sex hormone like testosterone or estrogen — it sits far above them. It is not GnRH, and it is not a GnRH drug — it acts one step upstream, turning GnRH on. And it is not a supplement, even though people search for "kisspeptin supplement"; it is an investigational research peptide, not a vitamin or a food product. There are two main research forms, kisspeptin-10 and kisspeptin-54, and the difference between them — covered below — mostly comes down to size and how long they last.
What is kisspeptin
What is kisspeptin, precisely? It is a family of neuropeptides encoded by the KISS1 gene on chromosome 1. The gene makes a 145-amino-acid precursor that is trimmed down to a 54-residue piece (kisspeptin-54) and shorter fragments, all of which share the same business end — a C-terminal RF-amide motif that the receptor recognizes. It is made in hypothalamic neurons (in the arcuate and AVPV nuclei), and also in the placenta and gonads. Its defining role is as the principal upstream activator of GnRH neurons: it is the signal that drives the GnRH pulses that run the whole hypothalamic-pituitary-gonadal (HPG) axis [4]. That role was nailed down by genetics — people and mice lacking a working receptor fail to enter puberty [4].
Kisspeptin-10
Kisspeptin-10 (KP-10) is the shortest active fragment — the final ten amino acids of the parent peptide, sequence Tyr-Asn-Trp-Asn-Ser-Phe-Gly-Leu-Arg-Phe-NH2 — and it retains full receptor activity because it carries the conserved RF-amide tail. Its older name is metastin, from the days when KISS1 was known only as a metastasis-suppressor gene. KP-10 is the form used in much of the male LH and testosterone work: an intravenous bolus produced maximal LH stimulation at 1 microgram/kg in healthy men [3]. Its practical catch is a short functional half-life — about 4 minutes in humans — so it is cleared fast and its effect is brief unless infused.
Kisspeptin-54
Kisspeptin-54 (KP-54) is the full 54-residue isoform — the same molecule originally named metastin in its 1996 discovery. It is larger and more resistant to the enzymes that chew up KP-10, giving it a longer half-life of about 27 to 28 minutes. That durability is why KP-54 is the form used in the fertility and brain studies: the IVF egg-maturation trigger (a single subcutaneous dose, around 9.6 nmol/kg optimal) [6], the restoration of LH pulses in hypothalamic amenorrhea [5], and the sexual-brain trials [8] all used KP-54. KP-10 and KP-54 thus split the work by their pharmacokinetics: KP-10 for short, sharp stimulation, KP-54 where longer action helps.
Kisspeptin supplement: why the term doesn't fit
"Kisspeptin supplement" is a common search, so it is worth saying plainly: kisspeptin is not a dietary supplement and is not sold or regulated as one. A supplement is a food product — a vitamin, mineral, or herbal extract — sold for general health. Kisspeptin is an investigational neuropeptide that acts on the body's master reproductive switch, studied only in supervised clinical trials with pharmaceutical-grade material, and approved by no regulator for any use [7]. It is not something taken orally as a tablet for wellness; the studied routes are injection, infusion, and a nasal spray. Treating it as a supplement misreads both what it is and the seriousness of the axis it acts on.