Ganirelix
GnRH antagonist
Also Antagon, Fyremadel, Orgalutran, Ganirelix acetate, Org 37462
- Evidence
- AStrong human evidence
- FDA status
- FDA approvedas of 2026-10-26
- Route
- Injection
- Studies cited
- 1 human0 animal or cell
It is an injection used in IVF to stop a woman ovulating too early. A trial of 313 women found pregnancy rates close to the older method, with fewer injections.
Sold for
Ganirelix is the IVF injection that stops the body ovulating before egg retrieval, replacing weeks of agonist down-regulation with a few days of antagonist.
Studies say
Randomized trials show pregnancy rates similar to the older leuprolide protocol with fewer injections, an A for its approved use.
Why grade A. Approval rested on randomized phase 3 trials against the standard long GnRH agonist protocol, including the North American trial cited here (313 women, ganirelix versus leuprolide), which found similar pregnancy rates with a shorter, simpler course. The label adds a 332-patient dose-finding trial and a larger open-label randomized trial against a GnRH agonist in which 463 women received ganirelix. 24
FDA. Approved. Ganirelix acetate injection was approved by the FDA in 1999 (originally as Antagon, Organon) for inhibiting premature LH surges in women undergoing controlled ovarian stimulation for fertility treatment. It is sold in the US as ganirelix acetate injection by Organon and others, and as Fyremadel (Ferring); the Antagon name is no longer used. 134
Written from 4 cited sources. Fact-checked 2026-10-27: 18 claims checked, 4 corrected. Last refreshed 2026-10-27. Not physician reviewed.
What this means for you
- What people take it for
- Stopping early ovulation during IVF
- Can a US doctor prescribe it?
- Yes, FDA approved for stopping early egg release during fertility treatment.
- Properly tested in people?
- Yes, in controlled trials, including one of 313 women.
Evidence checklist
- Randomised controlled trial Randomized vs leuprolide protocolyes
- Human study over 100 people North American trial, 313 womenyes
- More than one research group North American and European trialsyes
- Clinical outcomes, not surrogate markers Pregnancy rates measuredyes
- Human safety data beyond case reports Birth anomaly rates similar to agonist cyclesyes
Drawn from the cited studies below. A dash means the sources give no information.
What it is
Ganirelix is a lab-made peptide with ten amino acids. It is an altered form of gonadotropin-releasing hormone (GnRH). Some unnatural amino acids are swapped in. So it binds the GnRH receptor without switching it on. Organon developed it and it was approved in 1999. The brand name Antagon was dropped. Now it is sold as generic ganirelix acetate injection and as Fyremadel. 134
Doctors use it only in assisted reproduction. During ovarian stimulation, women take FSH shots (follicle-stimulating hormone). Rising estrogen can make the pituitary release a surge of luteinizing hormone (LH). That surge causes ovulation before the eggs can be retrieved. The drug stops the surge. 4
How it works
The hypothalamus sends pulses of GnRH. In response, the pituitary releases LH and FSH. Ganirelix competes with GnRH for its receptor on pituitary cells and blocks it. LH release falls within hours of the first injection. GnRH agonists such as leuprolide work the opposite way. They first overstimulate the receptor and then wear it out over one to two weeks. It acts at once. So doctors can start it partway through stimulation and stop it on the day of the ovulation trigger. Its effect also wears off quickly. 24
What human research shows
The North American phase 3 trial randomized 313 women at IVF centers. One group got ganirelix, started during stimulation. The other got leuprolide, started in the cycle before. Clinical pregnancy rates per attempt were 35.4% with ganirelix and 38.4% with leuprolide. Ongoing pregnancy rates were 30.8% and 36.4%. None of these gaps was statistically significant. Cycles with ganirelix were shorter. They used fewer shots. They gave slightly fewer eggs (11.6 versus 14.1 on average). Moderate and severe reactions at the injection site were less common with ganirelix. 2
The prescribing information sums up two more trials. One was a double-blind study of doses in 332 women. The other was an open-label randomized study in which 463 women received ganirelix, with a GnRH agonist as the reference treatment. Since then, plans built on ganirelix or cetrorelix have become the default in most IVF programs. One reason is that they allow a GnRH agonist as the ovulation trigger. That sharply cuts the risk of ovarian hyperstimulation syndrome (OHSS). 4
| Study | Model | Finding |
|---|---|---|
| North American Ganirelix Study Group | Humans, n=313, randomized open-label phase 3, ganirelix vs leuprolide in IVF | Ongoing pregnancy rates of 30.8% versus 36.4% were not significantly different; ganirelix cycles were shorter with fewer injections. 2 |
| Ganirelix acetate prescribing information | FDA label | Approved to inhibit premature LH surges in controlled ovarian stimulation; abdominal pain, headache and ovarian hyperstimulation syndrome were among the most frequent adverse events in trials. 4 |
Safety
The label pools trial data from 794 women. The most common adverse events were gynecological abdominal pain (4.8%), fetal death (3.7%, which means early pregnancy loss after IVF), headache (3.0%) and OHSS (2.4%). Injection-site reactions were reported in 1.1%. Women must not use it in pregnancy or if they are allergic to GnRH analogs. The label warns of possible allergic reactions, including severe allergy (anaphylaxis), after the first dose. One observational study covered more than 1,000 newborns. It compared birth defect rates after ganirelix cycles with past controls from agonist cycles. The rates were comparable. OHSS comes from the stimulation itself. It is not specific to ganirelix. 14
Questions for your clinician
- How does the antagonist protocol compare with the long agonist one for my case?
- What are the signs of ovarian hyperstimulation I should report?
- How many fewer eggs might I expect, and does it matter for my plan?
Questions people ask
Is ganirelix FDA-approved?
Yes, since 1999. It is used to prevent early LH surges in women having controlled ovarian stimulation. It is sold as ganirelix acetate injection and as Fyremadel. 13
How does ganirelix differ from leuprolide in IVF?
Leuprolide is a GnRH agonist. It takes one to two weeks to shut down the pituitary, so doctors start it the cycle before. Ganirelix is an antagonist that works within hours. Doctors start it mid-stimulation for a few days. Pregnancy rates were similar in the randomized trial. 2
Does ganirelix reduce the number of eggs?
In the North American trial, the ganirelix group averaged 11.6 eggs retrieved against 14.1 with leuprolide. Pregnancy rates did not differ significantly. 2
Is ganirelix the same as cetrorelix?
They are different molecules with the same action. Both are GnRH antagonists approved for the same IVF use. Trials have not shown a meaningful difference between them. 4
Citations
- Fyremadel (ganirelix acetate) prescribing information drugs.com
- Fluker 2001, Fertility and Sterility: efficacy and safety of ganirelix acetate versus leuprolide acetate in women undergoing controlled ovarian hyperstimulation (North American Ganirelix Study Group) doi.org
- Organon: ganirelix acetate injection product page organonpro.com
- Organon: ganirelix acetate injection prescribing information organon.com