Gonadorelin (GnRH): what it is, how it is used and what the evidence says

Gonadorelin is the pharmaceutical name for GnRH, the hormone at the top of the reproductive axis. Neurons in the hypothalamus release it in pulses into the tiny blood vessels that feed the pituitary; the pituitary responds by secreting luteinising hormone (LH) and follicle-stimulating hormone (FSH); and those two hormones act on the ovaries or testes to produce sex steroids, eggs and sperm. Andrew Schally’s group reported the isolation and properties of the FSH- and LH-releasing hormone in 1971 ^[1], and the synthetic peptide has been in clinical use since the 1970s.

It is a small molecule by the standards of this site: ten amino acids, with a pyroglutamate at one end and an amide at the other, and a molecular weight of about 1182 g/mol ^{[2] [11]}. The veterinary label for Factrel states that the product has the identical amino acid sequence and identical physiological activities to the endogenous hormone ^[2]. That is what distinguishes gonadorelin from the GnRH analogues: triptorelin, leuprorelin, goserelin and the rest are modified versions built to last longer and bind harder, and they are used to switch the axis off. Gonadorelin is the unmodified hormone, and it is used, in pulses, to switch the axis on.

Research vendors sell gonadorelin peptide as a freeze-dried powder, typically in 2 mg or 10 mg vials, and US compounding pharmacies supply it as a subcutaneous injection alongside testosterone. Neither is the same thing as the licensed diagnostic product ^[3]. Its neighbours on this site are HCG, which bypasses the pituitary altogether by acting directly on the testes or ovaries, HMG, which supplies FSH and LH themselves, and kisspeptin-10, which sits one step above GnRH in the same chain. Our guide to what research peptides are explains the research label.

The defining experiment was published in Science in 1978. Rhesus monkeys with hypothalamic lesions that abolished their own GnRH release were given synthetic GnRH either as a constant infusion or as one pulse an hour, the natural frequency. Continuous infusion failed to restore LH and FSH secretion; hourly pulses re-established it. When continuous delivery was started in animals whose gonadotropin secretion had been restored by pulses, secretion shut down again, a phenomenon the authors called desensitisation or down-regulation ^[4]. Ernst Knobil’s 1980 review built the modern picture of the menstrual cycle on this finding ^[5].

The consequence for anyone using gonadorelin is that the same peptide can produce opposite effects. Given as brief pulses roughly every 60 to 120 minutes, it drives LH and FSH release and, downstream, testosterone or oestrogen. Given continuously, or as a long-acting agonist, it first stimulates and then suppresses the pituitary, which is how GnRH agonists produce castrate testosterone levels in prostate cancer: the Trelstar label describes an initial surge in LH, FSH, testosterone and oestradiol followed, after two to four weeks of continuous exposure, by a sustained fall in LH and FSH and a marked reduction in testicular steroid production ^[12].

Gonadorelin itself does not last long enough to cause that suppression at ordinary doses: the UK SmPC gives a half-life of about four minutes, with rapid hydrolysis in plasma and excretion in urine ^[3]. A single injection therefore produces one burst of LH and FSH and is gone. This is why licensed use is either a single diagnostic dose or a programmable pump, and why the once- or twice-weekly injection schedules offered by compounders and research vendors do not reproduce either of the patterns studied in the literature.

The claimed gonadorelin benefits centre on restoring or protecting the body’s own LH, FSH and testosterone production. The evidence for that comes from pulsatile treatment of people whose hypothalamus does not make GnRH, a condition called idiopathic hypogonadotropic hypogonadism (IHH) or, when combined with loss of smell, Kallmann syndrome.

In the largest series, 76 men with IHH were treated with pulsatile GnRH through a subcutaneous pump for 12 to 24 months, starting at 5 to 25 ng/kg per pulse and titrated to normal adult testosterone. LH normalised in 97% and testosterone in 93%. Men who had some prior pubertal development achieved normal adult testicular size (92%) and sperm in the ejaculate (100%); men with adult-onset disease responded fastest, normalising testosterone by two months and completing spermatogenesis by six months. Men with no prior puberty did worse: their testicular volume and inhibin B never normalised over 24 months, their sperm counts plateaued at a median of 3 million/mL, and 18% remained azoospermic ^[7]. A 2014 meta-analysis of 16 GnRH studies in hypogonadotropic men found a 75% success rate for achieving sperm, similar to gonadotropin (HCG plus FSH) treatment ^[8].

In women, a 1990 clinical review from the Massachusetts General Hospital group described pulsatile GnRH as an effective alternative to gonadotropin injections in hypothalamic amenorrhoea and complete GnRH deficiency, with a high rate of ovulation and conception when a physiologically based pulse regimen is used, and lower ovulation rates in polycystic ovary syndrome. The authors suggested 75 ng/kg as a reasonable starting dose and a pulse frequency modelled on normal women ^[6]. Because the pituitary and ovary control the response, pulsatile GnRH produces mostly single ovulations and needs less monitoring than gonadotropins ^[6].

None of these studies involved men with a normal hypothalamus whose LH had been switched off by testosterone or anabolic steroids. That is the group buying gonadorelin for men from research vendors, and for them the evidence is the HCG literature, not this one. We found no randomised trial of gonadorelin as an adjunct to testosterone replacement therapy, and no study of gonadorelin for muscle, libido or fat loss in healthy men.

The licensed product in the UK is a 100 microgram vial for a single subcutaneous or intravenous injection, indicated for evaluating the functional capacity and response of the gonadotropes of the anterior pituitary. The LH response is used to test people with suspected gonadotropin deficiency, whether from the hypothalamus alone or with pituitary failure, and to assess residual pituitary function after removal of a pituitary tumour or after surgery or irradiation ^[3]. In children, the test helps distinguish central precocious puberty from benign early breast development; a 2025 study of 341 girls found that an LH peak above 4.7 IU/L after intravenous gonadorelin identified central precocious puberty with 100% sensitivity and 87% specificity, and noted that native GnRH is expensive and often unavailable, which is why a small dose of triptorelin is increasingly used as a substitute test ^[9].

Pulsatile pump treatment was licensed in the US as Lutrepulse and is still used in specialist centres, but that product is no longer listed. At the time of writing, the only gonadorelin product on the US DailyMed label database is Factrel, a Zoetis veterinary injection for ovarian follicular cysts and oestrus synchronisation in cattle ^[2]. Human use in the US therefore runs through compounding pharmacies, which supply gonadorelin as a subcutaneous injection to be given a few times a week with testosterone. That use is off-label, uncontrolled and, given the four-minute half-life, difficult to reconcile with the pulse physiology described above.

Research-vendor gonadorelin sits outside both. It has no marketing authorisation, is not batch-released, and the studies on this page were done with pharmaceutical peptide delivered by calibrated pumps or single measured doses.

The two are bought for the same purpose and work at different levels. HCG acts directly on the Leydig cells of the testis, mimicking LH, and lasts for a day or more; it raises intratesticular testosterone regardless of what the pituitary is doing, which is why a series of men on testosterone who added HCG kept their semen parameters over more than a year ^[13]. Gonadorelin acts on the pituitary and depends on the pituitary being able to respond. In a man on testosterone, the pituitary is suppressed by negative feedback, and a brief gonadorelin pulse can still evoke some LH release, which is the basis of the diagnostic test ^[3], but whether two or three subcutaneous injections a week produce enough LH to protect testicular function has not been measured in a trial.

The one clear advantage gonadorelin has over HCG is its size. As a ten-amino-acid peptide it is easy to synthesise and to verify by mass spectrometry, whereas HCG is a large glycoprotein that has to be standardised by bioassay. The clear disadvantage is the half-life. The HCG guide covers the male fertility-preservation series in detail; the comparison with gonadorelin is one of evidence versus none.

A single dose acts within minutes: in the diagnostic test, blood samples for LH are taken at baseline and over the following hour or so, and the 2025 paediatric study found LH peaks shortly after gonadorelin, earlier than the 180-minute peak seen with triptorelin ^[9]. Restoring fertility with pulsatile treatment is measured in months: two months to normal testosterone and six months to complete spermatogenesis in men with adult-onset disease, and much longer, or never, in men who had no puberty ^[7].

These figures are reported from the label and studies and are not recommendations. The UK diagnostic dose is 100 micrograms, subcutaneously or intravenously, once; in women with a menstrual cycle the test is done in the early follicular phase, days 1 to 7 ^[3]. Pulsatile treatment in men started at 5 to 25 ng/kg per pulse under the skin, delivered by a pump roughly every two hours and titrated to normal testosterone levels ^[7]. In women the review suggested 75 ng/kg per pulse at a frequency modelled on the normal cycle, with increases in non-responders ^[6]. For an 80 kg man, 25 ng/kg is 2 micrograms per pulse, or in the region of 25 micrograms a day.

Compounded and research-vendor protocols typically describe 100 to 200 micrograms injected two or three times a week. That is a diagnostic-sized dose given as a bolus, not a pulse regimen, and it has not been tested for any outcome. The peptide calculator can convert a 2 mg gonadorelin vial into micrograms per syringe unit, but a calculator cannot supply the missing evidence. Because the peptide lasts four minutes in plasma, the dose that reaches the pituitary from a subcutaneous injection is also uncertain.

Licensed gonadorelin is a powder reconstituted immediately before use and given under the skin or into a vein ^[3]. Pulsatile treatment uses a portable infusion pump connected to a subcutaneous or intravenous line ^{[6] [7]}. Nasal GnRH sprays have been studied historically, and because the peptide is small, nasal absorption is possible, but no nasal product is licensed in the markets PepFinder covers. Oral gonadorelin is not absorbed intact. Research vendors sell the acetate salt as a freeze-dried powder for reconstitution.

At the single diagnostic dose, the UK SmPC lists rare tachycardia, nausea, abdominal discomfort, headache, flushing, injection-site reactions and hypersensitivity, and notes that although allergic reactions have been seen with other polypeptide hormones, none had been encountered after a single 100 microgram diagnostic dose, with rare hypersensitivity reports after re-administration. It is contraindicated in known or suspected pregnancy ^[3]. The non-clinical package found no special hazard ^[3].

Long-term pulsatile treatment raises sex steroids to normal, so its effects are those of normal puberty or a normal cycle, which is the point; the pump line is the usual source of trouble. The larger safety question with gonadorelin bought online is the opposite of over-stimulation: if the injection pattern happens to produce sustained receptor occupancy, GnRH desensitises its own receptor ^[4], and the user could suppress rather than support the axis. There are no data either way, because the regimen has not been studied.

Unlicensed vials also carry the risks common to every research peptide: unknown purity, possible contamination and no batch release. A ten-amino-acid peptide is easy to test, which is an argument for insisting on a certificate of analysis rather than for skipping one.

Gonadorelin is a prescription-only medicine in the UK, licensed for diagnostic use (marketing authorisation PL 17509/0005) ^[3]. It is not a controlled drug under the Misuse of Drugs Act, unlike HCG and growth hormone, but supplying an unlicensed gonadorelin product is still a medicines offence; see the UK legal status page. In the US there is currently no FDA-approved human gonadorelin product on DailyMed ^[2]; compounded gonadorelin is regulated as compounding rather than as an approved drug, and the US legal status page explains how the FDA treats products sold as research chemicals. The legal status overview covers Canada, Australia and Europe.

For athletes, gonadorelin is named explicitly in section S2.2.1 of the WADA Prohibited List, testosterone-stimulating peptides in males, alongside chorionic gonadotrophin, LH, the GnRH agonist analogues and kisspeptin. It is prohibited at all times in men and not listed for women ^[10]. A vial sold as a research chemical is not a licensed medicine anywhere and is not covered by the safety data on this page.

The UK SmPC says to store the unopened vial below 25 °C, with a three-year shelf life; after reconstitution it is refrigerated and used within 24 hours, and any remainder discarded ^[3]. Trelstar and the other depot analogues have their own instructions, and they are different products. For research-grade powder the general rules in our guides to storing peptides and bacteriostatic water apply: cold, dry, dark, and refrigerated once in solution. The short in-use period on the licensed product is a reminder that the peptide is not stable in solution for long.

PepFinder does not sell gonadorelin. To compare research vendors, see gonadorelin prices, with UK and US listings. For a peptide this small, a mass-spectrometry identity check and an HPLC purity figure are straightforward, and a certificate of analysis should show a measured mass close to 1182 g/mol for the free peptide. Our guides to reading a peptide COA and third-party peptide testing explain what to look for, the third-party tested list shows which vendors publish results, and how to spot a fake peptide supplier covers the warning signs.