Overview
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In plain language
Ganirelix is a fertility drug, sold as Antagon, used during IVF to keep the ovaries from releasing eggs early. It is injected under the skin daily during the stimulation phase.
Like cetrorelix, it blocks the brain's GnRH switch directly and works immediately, with no initial hormone flare. The main difference between the two drugs is minor and practical; IVF clinics use whichever their protocol prefers.
For students
Ganirelix is a decapeptide GnRH antagonist (about 1,570 Da) with D-Nal at positions 2 and 3, D-4-chlorophenylalanine, D-3-pyridylalanine, and other non-standard residues that block the GnRH receptor without activating it. It is the second antagonist used in IVF, administered as a 250 mcg daily subcutaneous injection.
The antagonist protocol (ganirelix or cetrorelix plus gonadotropins) suppresses premature LH surges without the downregulation phase required by agonists, shortening IVF cycles and reducing gonadotropin doses. Meta-analyses and large registries show the two antagonists are effectively interchangeable; the choice is largely operational, an instructive example of clinical equivalence in a competitive market.
For researchers and instructors
Biochemistry. Shares the third-generation antagonist design principles with cetrorelix (reduced cationicity, position-2/3 hydrophobic D-residues); minor differences in position-5 and 8 substitutions tune duration and solubility.
Pharmacology. Daily dosing with rapid LH suppression; no flare; immediate reversibility; injection-site reactions (redness, swelling) are the most common adverse effect, reported in a substantial minority of patients.
Human evidence. Pivotal trials in controlled ovarian stimulation showed effective surge prevention and pregnancy rates comparable to the agonist long protocol; subsequent meta-analyses established antagonists as standard of care.
Teaching point. Illustrates clinical interchangeability of drugs within a mechanism class, and how protocol-level (not molecule-level) differences drive IVF prescribing.
Molecular identity
- Amino acids
- 10 (decapeptide, several D-residues)
- Molecular weight
- ~1,570 Da
- Formula
- C₈₀H₁₁₃ClN₁₈O₁₃
- Sequence
- Ac-D-Nal-D-Cpa-D-Pal-Ser-Tyr-D-Arg(Et)-Leu-His-Pro-D-Ala-NH2
Origin and history
Ganirelix (Antagon, Organon/Schering-Plough, now Merck) is the other widely used GnRH antagonist in IVF. Like cetrorelix it blocks the pituitary's GnRH receptors immediately, preventing premature LH surges.
It was approved in the U.S. in 1999 and is injected daily during the stimulation phase of an IVF cycle.
Key people
- Organon research teamDeveloped ganirelix
Timeline
- 1999
Antagon approved by the FDA
See every peptide on one history timeline.
Human evidence
Pivotal trials showed fewer premature ovulations and comparable pregnancy rates versus agonist long protocols.
Registration and enrollment are not proof of benefit; check study results directly.
Explore original publications and distinguish preclinical findings from controlled human evidence.
Safety and regulatory status
See every compound on the regulatory tracker.
FDA-approved. Given by subcutaneous injection; mild injection-site reactions are common.
This profile is educational and does not provide treatment, dosing or sourcing guidance.
Sources
- PubMed literature search: Ganirelix
- PubChem compound search: Ganirelix
- DailyMed (FDA label search): Ganirelix
- UniProt search: Ganirelix
- ClinicalTrials.gov search: Ganirelix
Hernandez Gener, E. (November 8, 2026). Ganirelix: molecular data, research history and evidence. VALREXA Biosciences. https://valrexa.com/peptides/ganirelix.html
APA style · Last reviewed November 8, 2026 · Our editorial standardsLast reviewed November 8, 2026. Trial and regulatory status can change; confirm in the linked registries. This profile is educational and is not medical advice, a treatment recommendation, or dosing or sourcing guidance. Report an error · Corrections policy