Gonadorelin
Synthetic GnRH, the hypothalamus's own signal for LH and FSH. Pumped in pulses every 60 to 120 minutes it restored ovulation and sperm production in trials; as an occasional injection beside testosterone it has never been studied.
Gonadorelin is gonadotropin-releasing hormone made synthetically: ten amino acids identical to the human hormone. Its effect depends on rhythm. Pulses make the pituitary release LH and FSH, continuous exposure shuts that response down, and in blood it lasts only minutes. Its US human brands, Factrel and Lutrepulse, are listed as discontinued; its approved use today is in cattle.
What is it?
Gonadorelin is the international name for synthetic gonadotropin-releasing hormone, the ten-amino-acid signal the hypothalamus sends to the pituitary. It is identical to the human hormone, so GnRH physiology is its pharmacology, and PubMed maps a search for gonadorelin onto its whole GnRH subject heading, about 43,300 records. The property that governs every use is rhythm. In rhesus monkeys whose own GnRH had been abolished, a constant infusion failed to restore LH and FSH, hourly pulses restored them, and switching back to a constant infusion desensitised the pituitary again. That is why gonadorelin is given in pulses to switch the reproductive axis on, while GnRH agonists given continuously switch it off, as the suppression pretreatment in one of the trials below did.
Pumps made it a fertility treatment. A small dose delivered every 60 to 120 minutes, through a vein or under the skin, imitates the hypothalamus. In the largest series, 292 women who were not ovulating received 600 cycles of intravenous pulses, most at 2.5 to 5 µg every 60 to 90 minutes: 75% of cycles ovulated, 18% produced a pregnancy, 3.8% of pregnancies were multiple and none caused ovarian hyperstimulation. The multicentre trial behind Lutrepulse, the US product for this use, reported ovulation in 91% and 96% of 109 women with primary and secondary hypothalamic amenorrhea, a 12% multiple-pregnancy rate and one case of hyperstimulation in a woman also given clomiphene. A 1988 series of 28 women resistant to clomiphene found both routes worked: all ovulated, subcutaneous pumping succeeded in 19 of 22 and intravenous pumping in all 17.
The same approach works in men whose GnRH signal never switched on, congenital hypogonadotropic hypogonadism. In a 2024 retrospective study of 45 men pumped 7 to 15 µg every 90 minutes for about 19 months, LH, FSH and testosterone rose and sperm appeared in 33 (73.3%); eight fathered children naturally and three more through assisted reproduction. A 2019 comparison of 28 men, not randomised, found that sperm appeared sooner on the pump than on hCG and hMG injections, at a median of 6 against 14 months, with similar success rates (90% and 83.3%). The costs were practical: skin reactions at the pump site were common in 2019, and the 2024 series recorded gynecomastia in 8 men, hardened skin in 6 and allergic reactions in 3.
The question most readers bring is whether gonadorelin can replace hCG for men on testosterone therapy, and no study has tested it. Every PubMed record that names gonadorelin together with testosterone in its title or abstract, 24 of them when we screened on September 28, 2026, concerns something else: pump therapy in hypogonadism, infants, animals or prostate cancer. Every human study with fertility outcomes delivered gonadorelin in pulses every 60 to 120 minutes, and the monkey experiment shows why the pattern matters. The two drugs also act at different levels. hCG acts on the testis directly and its terminal half-life after injection is about 29 hours (Ovidrel label); gonadorelin acts on the pituitary, whose LH output testosterone therapy suppresses, and it is gone from the blood within minutes. Whether an occasional injection can raise LH enough, for long enough, to keep testicular testosterone up has not been measured.
Gonadorelin was also a diagnostic: an injection shows how much LH the pituitary can release. In 865 girls with central precocious puberty, the peak LH after gonadorelin was lower in overweight and obese girls, so body weight changes how the test should be read. Two reports record allergy to the hormone itself: IgE antibodies against it in a woman on a Factrel infusion pump, and anaphylaxis with seizures within three minutes of an intravenous test dose in an eight-year-old girl, who recovered with treatment.
For anyone handling a vial, the stability data are good for a peptide, but they come from pharmaceutical formulations. Lutrepulse's gonadorelin acetate stayed stable for at least 18 months as a freeze-dried product at 24°C and for at least 45 days after reconstitution at 24°C or 37°C. In solution gonadorelin is most stable near pH 5; acetate buffer protected it, phosphate buffer sped its breakdown, and an acetate-buffered solution with mannitol had a predicted time to 90% potency of 9 years at 20°C. A compounded or unregulated vial has its own formulation and none of this testing.
Its approved use today is veterinary. US regulations list gonadorelin injections for cattle, for ovarian follicular cysts and for synchronising oestrous cycles before fixed-time insemination, on a veterinarian's order (21 CFR 522.1077). The cattle studies are some of its best-controlled data: in 558 dairy cows, four US products given at the same 100 µg dose ovulated 55.3% to 85.0% of animals although their LH curves could not be told apart. In sport, WADA's Prohibited List names GnRH and gonadorelin under S2.2.1 for males, and a 2023 review describes it as a drug misused in doping while surveying the methods laboratories use to detect it.
Mechanism of Action
Gonadorelin is the hormone itself, so its pharmacology is GnRH physiology: it binds GnRH receptors on the pituitary's gonadotroph cells, which answer with LH and FSH, and the timing of the signal decides whether that answer continues.
Pulses release LH and FSH
Each pulse makes the gonadotroph cells release LH and FSH. The fertility studies pulsed it every 60 to 120 minutes, and in one 1988 patient ovulation came only when the interval was cut to 60 minutes.
Continuous exposure shuts the axis down
In monkeys without their own GnRH, a constant infusion failed to restore gonadotropins, and after pulses had restored them, switching to a constant infusion desensitised the pituitary. GnRH agonists used for suppression rely on the same effect.
Testis and ovary respond downstream
Pumped gonadorelin restored ovulation in women and raised LH, FSH and testosterone and restored sperm production in men whose own GnRH signal was missing.
Cleared in minutes
Blood levels halve in 2.4 to 8 minutes in healthy people. In kidney failure the rapid phase lengthened to 12 to 16.5 minutes, which the authors attribute to the kidney's role in breaking it down, or to uraemia.
Published Research
PubMed maps a search for gonadorelin onto its whole GnRH subject heading, about 43,300 records, most about the body's own hormone and its analogues. Our evidence set holds 53 papers that name gonadorelin or GnRH; 19 name gonadorelin, Factrel, Lutrepulse or pulsatile GnRH in their titles and have an abstract, and 15 are carded below: 8 studies in people, 4 in cattle, 2 laboratory stability studies and 1 review. Four more, the human half-life measurements and the monkey experiment on pulse timing, are listed in the references because their titles call it GnRH or LH-RH.
Lutrepulse multicentre trial, 109 women
Women with primary or secondary hypothalamic amenorrhea received intravenous pulsatile gonadorelin acetate. Ovulation occurred in 91% and 96% of the two groups. IV-line complications ranged from 0% to 11% (mean 7%), 12% of pregnancies were multiple, and one woman who also took clomiphene had ovarian hyperstimulation. The authors judged it at least as effective as hMG, with lower overall risk.
600 pump cycles in 292 women
Women who were not ovulating received IV GnRH pulses between 1984 and 1993, mostly 2.5 to 5 µg every 60 to 90 minutes. Cycles ovulated 75% of the time and 18% produced a pregnancy; 3.8% of pregnancies were multiple and none followed agonist pretreatment, and there was no hyperstimulation. Results were better in hypogonadotropic women and worse in polycystic ovaries, where 45% of pregnancies miscarried, and in heavier women.
Clomiphene-resistant hypogonadotropic women, 28 patients
All 28 women ovulated and 16 conceived 20 pregnancies, two of them twins, with no miscarriages. Subcutaneous pumping worked in 19 of 22 and intravenous in all 17, usually at 90-minute intervals; one woman ovulated only at 60 minutes. Adding clomiphene increased pituitary sensitivity and caused hyperstimulation in one patient.
Pulsatile gonadorelin in men with congenital hypogonadism, 45 men
Men were pumped 7 to 15 µg of gonadorelin every 90 minutes and followed for about 19 months. LH, FSH and testosterone rose significantly and sperm appeared in 33 (73.3%); eight couples conceived naturally and three through assisted reproduction, while the six men with undescended testes did not reach normal testosterone. Side effects: gynecomastia 8, skin hardening 6, allergic reactions 3.
Gonadorelin pump vs hCG/hMG injections, 28 men
In a non-randomised comparison of azoospermic men with congenital hypogonadism, 10 used the pump and 18 injections. Sperm appeared sooner on the pump (median 6 vs 14 months) with similar overall success (90% vs 83.3%), and testicular growth did not differ. Injections gave higher testosterone with more acne and breast tenderness; skin reactions at the pump site were common.
The gonadorelin test and body weight, 865 girls
In girls with idiopathic central precocious puberty, the peak LH after gonadorelin stimulation was highest in normal-weight girls (median 9.1 mIU/mL) and lower in overweight (8.5) and obese girls (6.2), with a lower LH/FSH ratio in the obese. The authors recommend taking BMI into account when reading the test.
IgE allergy to a Factrel pump, one woman
A woman with severe hypogonadotropic hypogonadism on a gonadorelin hydrochloride (Factrel) infusion pump developed wheal-and-flare reactions at the injection sites. Skin-prick testing was positive for the hormone and negative for the vehicle, and her serum carried IgE antibodies to it: an allergy to GnRH itself.
Anaphylaxis during a gonadorelin test, one girl
An eight-year-old girl on triptorelin for central precocious puberty lost consciousness and had tonic seizures within 3 minutes of intravenous gonadorelin acetate given for a stimulation test. She recovered within 30 minutes with epinephrine, diphenhydramine and fluids. The authors advise giving the test where anaphylaxis can be treated.
Lutrepulse: purity and shelf life
Written after reports of reactions to pulsatile gonadorelin hydrochloride, this study followed the purity of gonadorelin acetate by HPLC. The drug substance was stable for at least 12 months at 24°C and 50% humidity, the freeze-dried product for at least 18 months, and the reconstituted solution for at least 45 days at 24°C or 37°C.
Gonadorelin in solution: pH and buffer
Stability-indicating HPLC showed gonadorelin, like triptorelin, is most stable near pH 5. Acetate buffer protected it and phosphate sped its breakdown, while ionic strength made no difference. An acetate-buffered solution (0.1 M, pH 5.0) with 3% mannitol had a predicted time to 90% potency of 9.0 years at 20°C.
Four US gonadorelin products in 558 dairy cows
Cows given 100 µg intramuscularly of Cystorelin, Factrel, Fertagyl or Ovacyst ovulated at different rates: 55.3% on Factrel against 73.6% to 85.0% on the others. LH peaks, timing and area under the curve did not differ detectably, and 100 µg released far more LH than 50 µg. No mechanism for the difference was shown.
Three Canadian products in cows and heifers
At 100 µg, Cystorelin produced higher mean and peak LH than Fertagyl or Factrel and more ovulations in Holstein cows (18/19 against 11/19 and 4/7), but not in beef heifers (6/10, 6/10 and 4/10). The next follicular wave emerged at the same time with all three.
Gonadorelin vs lecirelin and buserelin, 12 cows
In a crossover, 100 µg gonadorelin released less LH than lecirelin (25 or 50 µg) or buserelin (10 µg): its peak was about 2.5 times lower and came an hour earlier. The dominant follicle disappeared in 73% after gonadorelin against 82% to 100% with the analogues, a difference that was not significant, and progesterone rose about 70% with all.
200 vs 100 µg in 1,308 heifers
At the first GnRH of a 6-day CO-Synch program, 200 µg gonadorelin hydrochloride (Factrel) ovulated more heifers than 100 µg (54.7% vs 42.8%), and low progesterone at the time also favoured ovulation. Pregnancy per insemination did not differ between doses (59.6% vs 63.3%).
Detecting gonadorelin: analytical methods and doping
A review of chromatography, immunoassays and newer affinity sensors such as aptamers and molecularly imprinted polymers for small peptide hormones, using gonadorelin as the worked example because it has drawn attention as a therapeutic drug misused in doping during sports competitions.
Dosing Data
Gonadorelin has no current US human label. The doses below are the ones with published outcomes; every human row was delivered as pulses by pump.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
Side Effects & Contraindications
Reported Side Effects
From the studies above; there is no current US human label.
Contraindications & Cautions
No current label lists them; from the studies above, and a clinician decides.
Legal Status
Gonadorelin's US human approvals are discontinued; its cattle approval stands. The sport row below comes from the dataset.
Frequently Asked Questions
?Is gonadorelin the same as GnRH?
Yes. Gonadorelin is the name for synthetic gonadotropin-releasing hormone, with the same ten amino acids as the human hormone: pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2. Analogues change it so it lasts longer: D-Trp6-GnRH, the molecule sold as triptorelin, had a rapid-phase half-life of 18.7 minutes against 7.8 for GnRH in one study.
?Can gonadorelin replace hCG on testosterone therapy?
It has not been tested: none of the 24 PubMed records naming gonadorelin with testosterone, screened on September 28, 2026, studies that use. hCG acts on the testis directly and has a terminal half-life of about 29 hours; gonadorelin acts on the pituitary, whose LH output testosterone suppresses, and is gone within minutes. Every study that restored sperm with gonadorelin pumped it every 60 to 120 minutes.
?Is gonadorelin FDA-approved?
Not as a current human medicine. Drugs@FDA lists its two human brands, Factrel (1982) and Lutrepulse (1989), as discontinued. Gonadorelin injections are FDA-approved for cattle, for ovarian cysts and breeding synchronisation, on a veterinarian's order.
?Is gonadorelin banned in sport?
For men, yes: WADA's Prohibited List names GnRH and gonadorelin under S2.2.1, and the Legal table below gives the 2026 and 2027 entries. GnRH analogues are also on WADA's Monitoring Program for female athletes under 18, and a 2023 review describes gonadorelin as a drug misused in doping.
?How stable is gonadorelin once mixed?
Pharmaceutical gonadorelin acetate (Lutrepulse) stayed stable for at least 45 days after reconstitution at 24°C or 37°C, and in solution gonadorelin is most stable near pH 5, where acetate buffer protects it and phosphate speeds its breakdown. Those results belong to those formulations; a compounded or unregulated vial has not been tested.
?Can gonadorelin cause allergic reactions?
Rarely, but seriously: one woman on a Factrel pump developed IgE antibodies to the hormone, and an eight-year-old girl had anaphylaxis with seizures within three minutes of an intravenous test dose. Skin reactions at pump sites were common in a 2019 study, and 3 of 45 men in a 2024 series had allergic reactions.
References
- [fda-pi] US FDA, Drugs@FDA: Factrel (gonadorelin hydrochloride) NDA 018123, original approval September 30, 1982, and Lutrepulse (gonadorelin acetate) NDA 019687, original approval October 10, 1989; both listed as discontinued (read 2026-09-28).
- [fda-pi] 21 CFR 522.1077, Gonadorelin: injectable new animal drug for cattle (eCFR, as of 2026-09-01).
- [fda-pi] US FDA. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A, Categories 1-3 (updated May 14, 2026): gonadorelin not listed.
- [Human] Santoro N. "Efficacy and safety of intravenous pulsatile gonadotropin-releasing hormone: Lutrepulse for injection." Am J Obstet Gynecol, 1990;163(5 Pt 2):1759-64. PMID: 2122733.
- [Human] Filicori M, et al. "Treatment of anovulation with pulsatile gonadotropin-releasing hormone: prognostic factors and clinical results in 600 cycles." J Clin Endocrinol Metab, 1994;79(4):1215-20. PMID: 7962297.
- [Human] Blunt SM, et al. "Pulsatile GnRH therapy for the induction of ovulation in hypogonadotropic hypogonadism." Acta Endocrinol Suppl (Copenh), 1988;288:58-65. PMID: 3138867.
- [Human] Niu YH, et al. "[Effect and safety of pulsatile GnRH therapy for male congenital hypogonadotropic hypogonadism]." Zhonghua Nan Ke Xue, 2024;30(5):404-409. PMID: 39210488.
- [Human] Zhang L, et al. "The Pulsatile Gonadorelin Pump Induces Earlier Spermatogenesis Than Cyclical Gonadotropin Therapy in Congenital Hypogonadotropic Hypogonadism Men." Am J Mens Health, 2019;13(1):1557988318818280. PMID: 30569789.
- [Human] Fu JF, et al. "Impact of BMI on gonadorelin-stimulated LH peak in premenarcheal girls with idiopathic central precocious puberty." Obesity (Silver Spring), 2015;23(3):637-43. PMID: 25645648.
- [Human] Foster WG, et al. "Immunoglobulin-mediated hypersensitivity in response to long-term treatment with gonadorelin hydrochloride (Factrel) in a female patient." Am J Obstet Gynecol, 1989;160(4):979-83. PMID: 2653043.
- [Human] Akın O, et al. "Anaphylaxis to gonadorelin acetate in a girl with central precocious puberty." J Pediatr Endocrinol Metab, 2015;28(11-12):1387-9. PMID: 26197466.
- [In Vitro] Wong W, et al. "Stability and purity profile of gonadorelin acetate: a high-purity gonadotropin-releasing hormone." Int J Fertil, 1990;35(5):302-9. PMID: 1980667.
- [In Vitro] Helm VJ, et al. "Stability of gonadorelin and triptorelin in aqueous solution." Pharm Res, 1990;7(12):1253-6. PMID: 2151342.
- [Animal] Souza AH, et al. "Comparison of gonadorelin products in lactating dairy cows: efficacy based on induction of ovulation of an accessory follicle and circulating luteinizing hormone profiles." Theriogenology, 2009;72(2):271-9. PMID: 19394072.
- [Animal] Martínez M, et al. "The effects of 3 gonadorelin products on luteinizing hormone release, ovulation, and follicular wave emergence in cattle." Can Vet J, 2003;44(2):125-31. PMID: 12650040.
- [Animal] Picard-Hagen N, et al. "Effect of gonadorelin, lecirelin, and buserelin on LH surge, ovulation, and progesterone in cattle." Theriogenology, 2015;84(2):177-83. PMID: 25890780.
- [Animal] Melo DB, et al. "Effect of 200 μg of gonadorelin hydrochloride at the first GnRH of a CO-Synch program on ovulation rate and pregnancies per artificial insemination in Holstein heifers." J Dairy Sci, 2024;107(8):6268-6277. PMID: 38460874.
- [Review] Torrini F, et al. "Advances and perspectives in the analytical technology for small peptide hormones analysis: A glimpse to gonadorelin." J Pharm Biomed Anal, 2023;228:115312. PMID: 36858006.
- [Human] Fauconnier JP, et al. "Rate of disappearance in plasma of synthetic LH-RH intravenously injected in man." Gynecol Obstet Invest, 1978;9(5):229-37. PMID: 378777.
- [Human] Pimstone B, et al. "Metabolic clearance and plasma half disappearance time of exogenous gonadotropin releasing hormone in normal subjects and in patients with liver disease and chronic renal failure." J Clin Endocrinol Metab, 1977;44(2):356-60. PMID: 320223.
- [Human] Barron JL, et al. "Metabolic clearance and plasma half-disappearance time of D-TRP6 and exogenous luteinizing hormone-releasing hormone." J Clin Endocrinol Metab, 1982;54(6):1169-73. PMID: 6210706.
- [Animal] Belchetz PE, et al. "Hypophysial responses to continuous and intermittent delivery of hypopthalamic gonadotropin-releasing hormone." Science, 1978;202(4368):631-3. PMID: 100883.
Sources & Citations
Every PubMed citation on this page has been checked against its record. Drugs@FDA, the Code of Federal Regulations and FDA's 503A list were read on September 28, 2026. Grey Peptides sells nothing and links to no vendor.
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