Gonadorelin has a strange double life. In medicine it is one of the oldest peptide hormones in use — synthetic GnRH, the signal at the very top of the testosterone chain — and its defining property is that it only works when delivered in pulses, usually by a pump worn day and night. In gyms it is sold in vials as a way to keep the testes running during a steroid or testosterone cycle, or as a stand-in for hCG since hCG compounding ended in the US.
This page sets out what gonadorelin is, what its approved drugs were, what the trials in men measured, and what is missing. It reports research and gives no usage guidance, per our editorial standards.
What it is
Gonadorelin is a 10-amino-acid peptide with the same sequence as the gonadotropin-releasing hormone (GnRH) made in the hypothalamus. GnRH travels to the pituitary and makes it release LH and FSH; LH tells the testes to make testosterone, FSH supports sperm production. It is the rung below kisspeptin, which switches on the GnRH neurons, and above hCG, which mimics LH at the testis. The plain-language entry is Peptide Lexicon's gonadorelin page; this page is about the performance question.
Two US drugs, both discontinued
Drugs@FDA lists two gonadorelin products (openFDA drugsfda, read 2026-09-27):
| Drug | Application | Approved | Form | Status |
|---|---|---|---|---|
| Factrel (gonadorelin hydrochloride) | NDA 018123, now Hikma | 30 September 1982 | 0.1, 0.2 and 0.5 mg vials — a diagnostic test of pituitary response | Discontinued |
| Lutrepulse (gonadorelin acetate) | NDA 019687, Ferring | 10 October 1989 | 0.8 and 3.2 mg vials in a pump kit — pulsed delivery to induce ovulation | Discontinued |
So there is no marketed gonadorelin drug in the US. What is sold for gym use is research-labelled or compounded product. In veterinary medicine gonadorelin remains in wide use — cattle breeding programmes are a large share of its literature — which is part of why the peptide is cheap and easy to find.
The pulse rule
The finding that defines gonadorelin is from 1978. Belchetz and colleagues took rhesus monkeys whose hypothalamus had been lesioned so they made no GnRH of their own. A constant infusion of GnRH failed to restore LH and FSH. One pulse an hour — the natural rhythm — restored them. And switching animals that had recovered on pulses over to continuous delivery shut the pituitary down again. The authors put it down to "the pattern of GnRH delivery rather than … the amounts".
That result is why the two medical uses look so different:
- Pulsed gonadorelin switches the system on. It is used by pump in people whose hypothalamus does not make GnRH.
- Constant GnRH signalling switches it off. Long-acting GnRH agonists such as leuprolide exploit exactly this to suppress testosterone in prostate cancer. The same shape appears with kisspeptin one rung up: short exposures stimulate, sustained exposure suppresses (see kisspeptin).
What was measured in men
The human evidence is almost entirely in congenital hypogonadotropic hypogonadism — men born without working GnRH signalling.
- Zhang 2019, Am J Mens Health. 28 azoospermic men, nonrandomised: 10 on a pulsatile gonadorelin pump, 18 on hCG/hMG injections. Sperm appeared at a median of 6 months on the pump against 14 on injections; the proportion who produced sperm was similar (90% vs 83%). Testis volume grew in both groups. The injection group had more acne and breast tenderness, which the authors linked to higher testosterone.
That is a fertility result in men with a missing hormone, delivered by a pump around the clock. It is not a study of men with a working axis taking occasional injections while on steroids — the use the gym market describes. No trial found for this page tested gonadorelin in that setting, for testosterone, testicular size, sperm or anything else.
The muscle question has no data
PubMed, 2026-09-27. gonadorelin[tiab] returns 296 records, a large share of them in cattle and other animals. Restricted to human studies that also mention testosterone: 14, all titles read. None measured muscle size, lean mass or strength. They cover cryptorchidism in boys, the 2019 pump study, a laboratory assay — and three concern long-acting gonadorelin agonists used to suppress testosterone, in prostate cancer and in paraphilia, which is the pulse rule seen from the other side.
So a muscle claim is two inferences stacked: that gym-style dosing reproduces the pulsed effect seen by pump, and that the resulting testosterone would matter for muscle in someone already taking testosterone. Neither has been tested.
The hCG question
Much of the recent interest follows a regulatory change. On 23 March 2020 hCG became a biologic under US law, which ended its compounding by pharmacies; gonadorelin, a short peptide, did not move with it. The hCG side of that story, including its side-effect record in men, is on Peptifact's hCG side-effects page. The two drugs act on different rungs — gonadorelin needs a working pituitary to respond; hCG bypasses it — so one does not stand in for the other by design.
Status in sport
- WADA: gonadorelin is named in S2.2.1 — testosterone-stimulating peptides in males, alongside chorionic gonadotrophin, LH and kisspeptin — prohibited at all times. The section map is on WADA status by compound.
- Detection: the Cologne anti-doping laboratory's 2012 urine screen covers gonadorelin with desmopressin and nine growth-hormone-releasing peptides, at detection limits of 2–10 pg/mL (Thomas 2012); a 2023 review uses gonadorelin as the worked example of how peptide-hormone testing has developed (Torrini 2023). Testing context is on peptides and drug testing.
Dose figures, reported
The labelled amounts were 100, 200 and 500 micrograms per Factrel vial, for a single diagnostic injection, and 0.8 and 3.2 mg per Lutrepulse vial, dissolved and delivered by pump in small pulses through the day. Fertility pumps in men likewise deliver micro-doses in pulses through the day and night. These describe specialist medical use. The figures in circulation on vendor and forum pages are compiled on Peptifact's gonadorelin dosage page.
The honest summary
- Gonadorelin is synthetic GnRH, the top of the testosterone chain.
- Both US drugs — Factrel (1982) and Lutrepulse (1989) — are discontinued.
- It works only in pulses; continuous GnRH signalling shuts the pituitary down (Belchetz 1978).
- The human evidence is fertility in men born without GnRH, by pump: sperm at 6 months vs 14 on injections, in a nonrandomised study of 28.
- No study of gym-style use, and no muscle data — 14 human testosterone records, none measuring muscle.
- Prohibited in sport at all times (S2.2.1) and included in routine urine screens.
Limits of this page
The fertility study is small and not randomised. The PubMed counts depend on query wording and were taken on one date. Discontinued labels are summarised from Drugs@FDA's product records; the full prescribing texts were not available for this page. Pulse intervals for Lutrepulse are described in general terms rather than quoted from its withdrawn label.
Sources and dates
- U.S. Food and Drug Administration, Drugs@FDA via openFDA: NDA 018123 (Factrel; original approval 1982-09-30; all strengths discontinued) and NDA 019687 (Lutrepulse Kit; original approval 1989-10-10; discontinued), read 2026-09-27.
- Belchetz PE, Plant TM, Nakai Y, Keogh EJ, Knobil E. Hypophysial responses to continuous and intermittent delivery of hypothalamic gonadotropin-releasing hormone. Science 1978;202:631–3 — PMID 100883.
- Zhang L, Cai K, Wang Y, et al. The pulsatile gonadorelin pump induces earlier spermatogenesis than cyclical gonadotropin therapy in congenital hypogonadotropic hypogonadism men. Am J Mens Health 2019;13:1557988318818280 — PMID 30569789.
- Thomas A, Walpurgis K, Krug O, Schänzer W, Thevis M. Determination of prohibited, small peptides in urine for sports drug testing. J Chromatogr A 2012;1259:251–7 — PMID 22901302.
- Torrini F, Scarano S, Palladino P, Minunni M. 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.
- PubMed, searched 2026-09-27:
gonadorelin[tiab]→ 296;gonadorelin[tiab] AND testosterone[tiab] AND humans[mh]→ 14. - World Anti-Doping Agency, 2026 Prohibited List, S2.2.1 — as mapped on this site's WADA status by compound.