Ganirelix

Orgalutran (EU/UK/AU), Fyremadel, Antagon (former US name), ganirelix acetate injection (US generic), Org 37462

Sexual health, hormones & signalling

Awaiting medical reviewEN ES DE FR PT ZH+ Follow for updates

Note on this profile. Ganirelix is an approved prescription medicine used in fertility clinics, not a research-only compound. This page explains the published science. Use outside a supervised IVF cycle has no evidence base and carries the risks discussed below.

Summary

Class: Synthetic GnRH (LHRH) antagonist decapeptide (third generation), closely related to cetrorelix
Mechanism: Competitively blocks pituitary GnRH receptors, suppressing LH (and to a lesser extent FSH) within hours, without flare, reversible within 1–2 days of stopping
Routes studied: Subcutaneous injection only
Dose range reported: Approved: 0.25 mg SC once daily, started in the mid-follicular phase (usually stimulation day 5–6) and continued until the day of trigger. Dose-finding trials tested 0.0625–2 mg; higher doses lowered implantation rates. Community use: anecdotal
Half-life: ~13 h after a single dose; ~16 h at steady state; bioavailability ~91%
Storage: Pre-filled syringe: room temperature per label (do not freeze), protect from light; no reconstitution
Regulatory status: Approved medicine (US 1999, EU 2000, UK, AU, ZA and others)

Doses are as reported in studies or by the community — never recommendations.

1What it is

Ganirelix is one of two injectable GnRH antagonists used in IVF, developed by Organon (now Merck/MSD and others). Like cetrorelix it blocks the pituitary's GnRH receptor so that a woman's own LH surge cannot release eggs before the clinic is ready to collect them. It arrives as a ready-to-use pre-filled syringe, which is one practical reason it is more common than cetrorelix in US clinics. It has no approved use outside controlled ovarian stimulation.

2How it's thought to work

Competitive, reversible blockade of the GnRH receptor. Within about 4 hours of the first 0.25 mg dose LH falls by roughly half, and FSH by less; levels recover within about 48 hours of the last injection.

Dose-finding work showed an unexpected trade-off: higher doses (1–2 mg) suppressed LH more completely but produced lower oestradiol and lower implantation rates, suggesting that some LH activity is needed for normal follicle and endometrial development. This is why 0.25 mg became the fixed dose.

A GnRH trigger still works in a ganirelix cycle (the agonist displaces the antagonist and activates the receptor briefly), which is the basis of "OHSS-free" antagonist protocols.

Competitive blockade of the pituitary GnRH receptor. Suppression is dose-dependent and reverses within days of the last dose, so the ovary's own cycle resumes quickly.Schematic — not to scale

3What the research shows

Prevention of premature LH surge in IVF

The dose-finding trial (n=333) established 0.25 mg as optimal, with premature LH rises in <2% of cycles and the highest implantation rate (Ganirelix Dose-Finding Study Group 1998, Hum Reprod). Against a leuprolide long protocol, ganirelix gave shorter stimulation, lower FSH use and similar ongoing pregnancy rates (North American Ganirelix Study Group 2001, Fertil Steril). A European trial against buserelin (n=730) found a numerically lower but not statistically different ongoing pregnancy rate (European Orgalutran Study Group 2000, Hum Reprod). Pooled across antagonists, Cochrane found live-birth rates comparable to protocols and markedly lower OHSS (Al-Inany 2016). [4]

Treatment of early-onset severe OHSS

Re-starting ganirelix in the luteal phase of cycles with early severe OHSS, with embryo freezing, led to rapid regression of OHSS in small case series (Lainas 2007, Reprod Biomed Online). Off-label, small, uncontrolled. [5]

Graded A/B

Oocyte donation and fertility preservation cycles

Antagonist protocols with ganirelix are standard in donor and random-start fertility-preservation cycles because they allow stimulation to begin at any cycle phase; evidence is largely observational and class-level.

Any non-IVF indication

None studied. Unlike cetrorelix, ganirelix was never developed for BPH, endometriosis or cancer.

4Reported side effects and interactions

Literature-reported

Common (literature; US label, n≈1,000 cycles). abdominal pain of gynaecological origin (~5%), headache (~3%), ovarian hyperstimulation syndrome (~2%), vaginal bleeding, injection-site reactions (~1%, mostly redness and itching), nausea. The label also lists fetal death (~4%) as an adverse event observed in trials; this rate is in line with general IVF populations and has not been attributed to the drug.

Serious / warnings. hypersensitivity reactions including rare anaphylaxis, sometimes after the first dose; contraindicated in pregnancy (ganirelix cycles are monitored to exclude pregnancy before starting) and breastfeeding. The needle shield of some presentations contains natural rubber latex, relevant to latex-allergic users. Congenital anomaly rates are comparable to other assisted-reproduction cohorts.

Community-reported

essentially confined to IVF patients: stinging and bruising at the site, headaches, mood swings (hard to separate from the stimulation drugs).

Theoretical. prolonged use would suppress oestrogen or testosterone with the same bone, mood and metabolic consequences as ; untested.

Interactions. no formal studies. Peptidase metabolism makes pharmacokinetic interactions unlikely. Pharmacodynamically blocks gonadorelin and kisspeptin effects.

Markers researchers commonly monitor

IVF cycle monitoring is the only evidence-based context: No markers are established for any use outside fertility treatment.

Marker	Why it's watched
LH	suppression is the drug's purpose; a premature rise (>10 IU/L) or progesterone rise signals breakthrough.
Oestradiol	follicular development and OHSS risk; a transient dip after the first ganirelix dose is expected.
Progesterone (late follicular)	premature luteinisation predicts poorer fresh-transfer outcomes.
Transvaginal ultrasound	follicle size and count govern when ganirelix starts and when to trigger.
Pregnancy test; OHSS symptoms (abdominal girth, weight, urine output)	post-trigger.
Haematocrit, sodium, creatinine, liver enzymes	only if OHSS develops.

Free for everyone. Safety information is never behind a paywall.

5Reconstitution and handling

Supplied as a 0.25 mg/0.5 mL pre-filled syringe; no mixing. Injected subcutaneously into the upper thigh or lower abdomen at roughly the same time each day; the label advises the timing be kept consistent, and the last dose is given on the morning of the trigger day in most protocols. The dose is fixed, so the calculator is not applicable.

Open in calculator, pre-loaded →

6Commonly studied alongside

Cetrorelix (interchangeable antagonist), recombinant FSH/HMG, HCG and GnRH agonist triggers (triptorelin, leuprolide), progesterone luteal support, kisspeptin-54 (experimental trigger in antagonist cycles).

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	FDA-approved (ganirelix acetate injection; generics available) for inhibition of premature LH surges in women undergoing controlled ovarian stimulation
European Union	EMA-authorised (Orgalutran, Fyremadel)
United Kingdom	MHRA-licensed (Orgalutran, Fyremadel); prescription-only
Australia	TGA-approved (Orgalutran); S4
South Africa	SAHPRA-registered (Orgalutran); prescription-only
Sport	Not specifically listed by WADA as of review date †

8Open questions

Whether a fixed 0.25 mg dose is optimal for all body weights (pharmacokinetic data suggest higher exposure in lighter women).
Fixed versus flexible start day; evidence is mixed and clinic-specific.
No data on use outside controlled ovarian stimulation.

9References

1The Ganirelix Dose-Finding Study Group (1998). A double-blind, randomized, dose-finding study to assess the efficacy of the gonadotrophin-releasing hormone antagonist ganirelix (Org 37462) to prevent premature luteinizing hormone surges in women undergoing ovarian stimulation with recombinant follicle stimulating hormone (Puregon). Hum Reprod. PubMed
2The European Orgalutran Study Group; Borm G, Mannaerts B (2000). Treatment with the gonadotrophin-releasing hormone antagonist ganirelix in women undergoing ovarian stimulation with recombinant follicle stimulating hormone is effective, safe and convenient: results of a controlled, randomized, multicentre trial. Hum Reprod. PubMed
3The North American Ganirelix Study Group (2001). Efficacy and safety of ganirelix acetate versus leuprolide acetate in women undergoing controlled ovarian hyperstimulation. Fertil Steril. PubMed
4Al-Inany HG et al. (2016). Gonadotrophin-releasing hormone antagonists for assisted reproductive technology. Cochrane Database Syst Rev. PubMed · DOI
5Lainas TG et al. (2007). Management of severe early ovarian hyperstimulation syndrome by re-initiation of GnRH antagonist. Reprod Biomed Online. PubMed · DOI
6Ganirelix acetate injection / Orgalutran prescribing information and SmPC (current). PubMed

References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.

† Being confirmed by our reviewers against current sources.

10Community

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Self-reported side effects Phase 2

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11Page history

26 Oct 2026Profile published — awaiting medical review

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