# Kisspeptin: The Upstream Switch That Fires GnRH, LH and Testosterone > Kisspeptin is the KISS1 gene product that turns on the body's own GnRH neurons, driving LH, FSH and testosterone. A data-forward digest of the measured human and animal readouts, each cited to source. A data-forward digest of the reproductive neuropeptide: every endocrine readout led with the number and attributed to the study, the population and the route. Investigational, never approved, and defined by one hard limit — tachyphylaxis. ## The short version Kisspeptin is a small protein the body makes in the brain. It is the on-switch for the whole reproductive hormone system. When kisspeptin lands on its docking site (a receptor called KISS1R, older name GPR54), it tells a set of brain cells to release GnRH — the hormone that orders the pituitary gland to make LH and FSH, which in turn drive testosterone in men and ovulation in women. So kisspeptin sits one step above everything else: it does not supply those hormones, it turns on the cells that do. Researchers give kisspeptin to study how this switch works. In healthy men it raised LH and testosterone [3]. In women who had stopped menstruating it restarted hormone pulses [4]. In IVF it triggered eggs to mature without the dangerous over-stimulation that older drugs can cause [5]. The catch: push it too hard or too long and the switch stops answering — an effect called tachyphylaxis [4][16]. No version of kisspeptin is an approved medicine, and it is not a supplement. What people report — including the downsides — is on [the effects page](/effects). ## What the kisspeptin literature has measured Kisspeptin is the product of the KISS1 gene, a [kisspeptin peptide](/what-is-kisspeptin) family that includes a 54-residue form (kisspeptin-54, first named metastin) and a shorter 10-residue fragment (kisspeptin-10). Both share a tail motif — the C-terminal RF-amide — that lets them bind KISS1R (formerly GPR54), a receptor sitting on the GnRH-releasing neurons of the hypothalamus (the brain's hormone-control hub). Activation there opens a calcium cascade that makes those neurons fire and release GnRH in pulses [2]. That single mechanism is the spine of the whole record. Loss-of-function mutations in GPR54 abolish puberty in humans, and deleting the receptor in mice reproduces the same failure — the finding that, in 2003, recast kisspeptin from a cancer gene into the master upstream switch of reproduction [1]. Give kisspeptin to a healthy adult and the downstream hormones move in a predictable order: LH rises first and most, FSH less, testosterone last [8]. The numbers are specific. In healthy men, an intravenous kisspeptin-10 bolus drove LH from 4.1 to 12.4 IU/L, and a higher infusion raised serum testosterone from 16.6 to 24.0 nmol/L [3]. A 90-minute kisspeptin-54 infusion roughly doubled mean LH versus saline [8]. These are lab readouts in supervised research, not a protocol anyone should copy. ## Kisspeptin, GnRH and the sex steroids are not the same thing A recurring confusion is worth settling up front. Kisspeptin is a neuropeptide that acts on KISS1R. GnRH is the next molecule down the chain, released *because of* kisspeptin, acting on a different receptor in the pituitary. LH, FSH and testosterone are the downstream readouts — the outputs the system produces, not kisspeptin itself. Kisspeptin is therefore not a GnRH drug and not a sex hormone; it is the signal that switches the body's own GnRH on [1]. The naming history reinforces the point. KISS1 was first found in 1996 as a gene that suppresses cancer spread — its product was called metastin — and only later understood as the trigger of the reproductive axis [13]. Same gene, two stories. This site reads the reproductive story: how a brain-made switch drives pulsatile [Kisspeptin research](/research) on the hormone axis, what it has measured, and where the evidence stops. ## What this site is — and is not This is an editorial monograph. It compiles the peer-reviewed kisspeptin literature, leads each claim with the measured value, and attributes that value to its study, the population studied and the route given. It is not a clinic, not a pharmacy, and not a vendor. No dose here is a recommendation; every dose is reported as what was administered to which population by which route. The honest framing matters because the data is uneven. Human work is real but comes largely from a small number of research centres, the exposures are short, and there are no Phase 3 trials and no regulatory approvals for any use [7]. Real-world anecdotal reports are thin precisely because kisspeptin is investigational rather than a sold consumer product. The [Kisspeptin effects](/effects) page lays out both the cited findings and the sparse community reports, kept clearly apart. Where the literature is precise, this site is precise; where it is silent, it says so. --- A data-forward monograph of the kisspeptin literature — every endocrine readout logged to its study, population and route, with the tachyphylaxis ceiling and the investigational status kept in plain view; no clinic behind the page and nothing here dosed, prescribed, or sold.