Gonadorelin

What gonadorelin is

The reproductive hormone axis begins in the hypothalamus. There, nerve cells produce GnRH, gonadotropin-releasing hormone, also called LHRH. It travels to the pituitary gland and triggers the release of LH and FSH there. In men, LH stimulates testosterone production in the testes, FSH stimulates sperm production. Andrew Schally received the Nobel Prize in 1977 for the discovery of this hormone.

Gonadorelin is chemically identical to the endogenous GnRH, a peptide of 10 amino acids. It is therefore not a modified analog like the drugs used in prostate cancer to suppress hormones, but the original. In the body it is broken down very quickly; according to the summary of product characteristics, its half-life is less than 10 minutes.

How it works and why the rhythm is everything

The hypothalamus does not release GnRH evenly, but in bursts lasting about one minute, at intervals of 60 to 120 minutes. The pituitary gland is tuned to this pattern. How important it is was shown in 1978 by an experiment in rhesus monkeys whose own GnRH production had been switched off: hourly pulses restored hormone release, a continuous infusion did not. When pulses were switched to continuous administration, the pituitary gland became desensitized.

This principle applies equally in humans. The summary of product characteristics describes that repeated high doses or a continuous infusion inhibit gonadotropin release, a paradoxical antifertility effect. After a single injection, LH and FSH reach their maximum after about 30 minutes and then fall again. Therapeutically, gonadorelin is therefore given via a small pump that mimics the natural pulse rhythm.

What it is used for

Medically, gonadorelin has two roles. As a test, it shows whether a hormonal disorder lies in the brain, in the pituitary gland or in the gonads. As pump therapy, it replaces the missing signal in people whose hypothalamus produces no GnRH, for example in congenital hypogonadotropic hypogonadism or in hypothalamic absence of menstruation.

In the scene, the idea is a different one. Anyone who supplies testosterone from outside shuts down their own axis: LH and FSH fall, the testes shrink, sperm production declines. As an add-on, gonadorelin is supposed to provide the signal from above and keep the testes active, as an alternative to hCG, which stimulates the testes directly. In addition, it is used in protocols intended to restart the body’s own production after stopping testosterone or anabolic steroids.

What the studies show

Pulses versus continuous administration, Science 1978

Belchetz, Knobil and colleagues gave rhesus monkeys whose GnRH production had been switched off the hormone either as a continuous infusion or as an hourly pulse. Only the pulses restored the release of LH and FSH, regardless of the total amount. A subsequent switch to continuous administration caused the release to collapse again. The work is an animal experiment, but it explains why GnRH is given therapeutically by pump in a pulse rhythm.

Pump versus gonadotropins, 202 patients, 2017

Mao and colleagues retrospectively analyzed 202 men with congenital hypogonadotropic hypogonadism, 20 with a GnRH pump, 182 with hCG and HMG. Under the pump, the first sperm appeared after a median of 6 months, under gonadotropins after 18 months. Testosterone, however, was lower under the pump, 8.3 versus 16.2 nanomoles per liter. The study was not randomized, and the groups were very unequal in size.

Meta-analysis, 420 patients, 2021

Wei and colleagues pooled 7 comparative studies with 420 patients. Pump therapy led to sperm 5.30 months earlier and to larger testes. There was no significant difference in whether sperm appeared at all, in sperm concentration or in the pregnancy rate. Allergic reactions occurred more often under GnRH, breast enlargement and acne more often under gonadotropins.

Where the data stop

The gap lies precisely in the use in the scene. No controlled study was found on gonadorelin as an add-on to testosterone therapy in otherwise healthy men. A 2026 review of peptide strategies for fertility loss under testosterone rates the clinical evidence for gonadorelin as limited, points to the necessary pulsatile administration and reserves GnRH therapy for specific indications, not for routine use under testosterone. For hCG, by contrast, there are several studies showing preservation of sperm production under testosterone.

Added to this is a physiological problem. The documented effect depends on pulses at intervals of one to two hours, around the clock, via a pump. A single injection produces a single short rise in LH. Whether a few injections per day or week are enough to keep the testes active under testosterone has not been tested by anyone. The data on pump therapy are also predominantly retrospective and not randomized.

Status, approval and legal

Gonadorelin is approved in Germany and available on prescription only, as a diagnostic agent and for pulsatile treatment in GnRH deficiency. Its use as an add-on to testosterone therapy is an unapproved use, often via compounded preparations or gray-market products. Information on use and dosing is omitted here. The World Anti-Doping Agency’s 2026 Prohibited List includes gonadorelin under S2.2.1 as a testosterone-stimulating peptide in men, prohibited at all times. The summary of product characteristics itself points out that use can lead to positive results in doping tests.

Safety

From decades of use, the side-effect profile is well known. The summary of product characteristics lists headache, abdominal pain, nausea and reactions at the injection site. Allergic reactions occur occasionally, and in isolated cases anaphylactic shock during pulsatile treatment. In people with a pituitary adenoma, bleeding into the pituitary gland has been described. Gonadorelin is contraindicated during pregnancy. With impaired liver or kidney function it has a stronger effect. Important for the scene: overly frequent or overly high doses can inhibit the axis instead of stimulating it. Hormone treatments belong under medical supervision with laboratory checks.

Sources

• Summary of product characteristics LHRH Ferring 0.1 mg/1 ml solution for injection, version September 2014
• Belchetz PE et al., Science 1978 — continuous versus pulsatile administration of GnRH in rhesus monkeys
• Mao JF et al., Asian Journal of Andrology 2017 — pump versus gonadotropins, 202 patients
• Wei C et al., World Journal of Mens Health 2021 — meta-analysis, 420 patients
• Cretu AM et al., Frontiers in Reproductive Health 2026 — peptide strategies for fertility loss under testosterone
• Hochu G et al., Translational Andrology and Urology 2025 — preserving sperm production under testosterone, including with hCG
• Jiang H et al., Translational Andrology and Urology 2025 — GnRH pump in 54 adult men
• Grujić M et al., Cureus 2024 — Andrew Schally and the discovery of LHRH
• Gelbe Liste — active substance gonadorelin, products and indications
• WADA Prohibited List 2026, officially published in the Austrian Federal Law Gazette III No. 219/2025