RESEARCH MONOGRAPH · KDC-MN-286

Ganirelix

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

73/100

Cetrorelix's slightly faster sibling, mostly a single-indication peptide but a clean tool inside that lane

Ganirelix (Orgalutran/Antagon) is structurally similar to cetrorelix but with different D-amino acid substitutions, and Organon developed it specifically for the IVF use case. The pitch is fast onset, predictable suppression of the premature LH surge during controlled ovarian stimulation, and a relatively short half-life that gives you tighter control of the suppression window. In that lane it's a clean compound.

The mechanism is standard third-generation GnRH antagonism. Competitive receptor blockade, no flare phase, dose-dependent suppression of LH and FSH that's measurable within hours of subcutaneous administration. Where ganirelix differs from cetrorelix is in the elimination kinetics: shorter terminal half-life (around 12-16 hours) and a tighter once-daily dosing window during the stimulation phase.

The clinical evidence is genuinely solid within IVF. Multiple phase 3 trials in the late 90s and early 2000s established equivalence to long agonist protocols for pregnancy rates while reducing the duration of suppression and the total gonadotropin dose required. The Ganirelix Dose-Finding Study Group work from that era is the reference.

What we like: fast on, fast off, and the cleanness of the antagonist mechanism for any research model where you want to study the LH surge specifically. If you're doing endocrine work where the flare confound matters, ganirelix is a useful comparator to the agonists in the class.

What we dont love is the narrow indication footprint. Unlike cetrorelix which has a broader research-use history, ganirelix has been primarily an IVF tool. That means the off-IVF literature is thinner, and the comparative pharmacology work versus other GnRH antagonists at non-fertility doses is limited. We've got less to lean on for HPG axis work outside reproduction.

Sourcing is okay but not great. Ganirelix acetate research material is available but the supplier list is shorter than for cetrorelix, and the QC variance can be a little wider. The peptide itself isnt particularly hard to synthesize (10 residues with the standard D-substitution pattern) but the pharma-grade reference is hard to compare against if you're trying to validate a research batch.

For a research lab working on the GnRH antagonist class, cetrorelix is usually the workhorse and ganirelix is the specialty pick when the pharmacokinetic window matters specifically.

Evidence: 78
Mechanism: 88
Reliability: 82
Safety: 78
Sourcing: 65
Value: 65
Signal: 60
Staying power: 65

Plain-language summary Intrigue 40 / 100

Ganirelix (Antagon, Orgalutran) is the second commercial GnRH antagonist, mechanistically identical to cetrorelix and used in the same IVF protocols for the same purpose: blocking the premature LH surge. The two drugs differ in fine structure and pharmacokinetics (ganirelix has a slightly shorter half-life), but in practice clinicians choose between them based on availability, formulation preference, and cost. Same dosing schedule, same side effect profile, same indication. The choice between cetrorelix and ganirelix mostly does not matter clinically. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Synthetic GnRH antagonist

A synthetic GnRH receptor antagonist; mechanistically similar to cetrorelix and used in the same IVF protocols.

Abstract

Ganirelix (Ac-D-2-Nal-D-Cpa-D-Pal-Ser-Tyr-D-(Et)2HArg-Leu-(Et)2HArg-Pro-D-Ala-NH2; CAS 124904-93-4; molecular formula C80H113ClN18O13; molecular weight 1570.35) is a synthetic GnRH antagonist decapeptide developed at Organon and approved by the FDA in 1999 under the trade name Antagon (US) and Orgalutran (EU). Mechanism is identical to cetrorelix: competitive GnRH receptor antagonism producing immediate dose-dependent LH and FSH suppression. Structurally distinct from cetrorelix by the diethylhomoarginine residues at positions 6 and 8. Plasma half-life is approximately 13 hours after subcutaneous dosing, shorter than cetrorelix but adequate for daily IVF protocol dosing. Approved for prevention of premature LH surge in controlled ovarian stimulation for IVF. Comparable clinical efficacy to cetrorelix in head-to-head trials. Used as an alternative GnRH antagonist in IVF and HPG suppression research.

Mechanism of action

Competitive GnRH receptor antagonism; mechanism identical to cetrorelix with shorter plasma half-life.

Reported research dose ranges

Clinical IVF 0.25 mg subcutaneous from stimulation day 5 through hCG trigger.

References

Borm G, Mannaerts B, et al. Treatment with the gonadotrophin-releasing hormone antagonist ganirelix in women undergoing ovarian stimulation. Hum Reprod 2000.
Oberye JJ, et al. Pharmacokinetic and pharmacodynamic characteristics of ganirelix. Fertil Steril 1999.
Fluker M, et al. Efficacy and safety of ganirelix acetate versus leuprolide acetate in women undergoing controlled ovarian stimulation. Fertil Steril 2001.

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The full reference document is available as a research-use-only PDF download. Note: PDFs for newly added compounds may take a few hours to propagate after this article was published.

KDC-MN-286

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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Ganirelix

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Mechanism of action

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Abstract

Mechanism of action

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References

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