Ganirelix

Ganirelix is a synthetic decapeptide GnRH receptor antagonist, structurally related to Cetrorelix, also built on this site, but modified at six sequence positions (1, 2, 3, 6, 8, and 10) rather than Cetrorelix's five. Ganirelix's specific modifications include N-acetyl-3-(2-naphthyl)-D-alanine at position 1, 4-chloro-D-phenylalanine at position 2, 3-(3-pyridyl)-D-alanine at position 3, and N,N-diethyl-homoarginine substitutions at both positions 6 (D-form) and 8 (L-form) — this dual homoarginine substitution at two separate positions is the specific structural feature distinguishing Ganirelix from Cetrorelix, which instead uses D-citrulline at position 6 alone and leaves position 8 as native arginine.

At Verified Peptides, we want to reiterate the same mechanistic-category point made in this site's Cetrorelix profile: Ganirelix is a GnRH ANTAGONIST, not an agonist, mechanistically distinct from Gonadorelin, Triptorelin, Alarelin, Leuprolide Acetate, and Buserelin (the agonists profiled elsewhere in this catalog), despite all targeting the same GnRH receptor.

Chemically, Ganirelix has molecular formula C80H113ClN18O13, molecular weight approximately 1570.35 g/mol, CAS number 124904-93-4, PubChem CID 16186319. It was developed by N.V. Organon (now part of Merck/MSD) and received FDA approval in 1999 (originally marketed as Antagon, now as Ganirelix Acetate Injection), with European Commission marketing authorization following in May 2000 under the brand name Orgalutran.

We independently cross-checked Ganirelix's molecular weight against its formula: C80H113ClN18O13 sums to approximately 1570.35 g/mol using standard atomic masses (80 carbon at 12.011, 113 hydrogen at 1.008, 1 chlorine at 35.453, 18 nitrogen at 14.007, 13 oxygen at 15.999), consistent with the vendor- and literature-reported figure, giving us confidence in this compound's chemical identifiers without needing to flag any discrepancy, unlike the vendor inconsistency we identified and corrected for Alarelin elsewhere in this phase.

At Verified Peptides, we think Ganirelix has a substantial clinical evidence base directly comparable in scale to Cetrorelix's, reflecting its status as one of the two original FDA-approved GnRH antagonists for ovarian stimulation. The key pivotal citation is the European Orgalutran Study Group (2000, Human Reproduction, PMID 10875855, volume 15, issue 7, pages 1490-1498), a multicentre, open-label, randomized non-inferiority study comparing Ganirelix against a long protocol using the GnRH agonist Buserelin (also built elsewhere in this catalog) combined with recombinant FSH. The study found mean implantation rates of 15.7% (Ganirelix) versus 21.8% (Buserelin reference) and ongoing pregnancy rates per attempt of 20.3% versus 25.7% respectively — meaning Ganirelix showed somewhat lower per-cycle success rates than the long agonist protocol in this specific trial. However, Ganirelix's ovarian hyperstimulation syndrome rate was substantially lower (2.4% versus 5.9% in the Buserelin reference group), illustrating the genuine efficacy-versus-safety tradeoff that has been a recurring theme in comparing antagonist and long-agonist IVF stimulation protocols since these early pivotal trials.

We also want to note that Ganirelix's clinical development followed a structured, dose-finding pathway: an initial double-blinded, randomized, dose-finding study across six different dosages (0.0625 mg to 2 mg) in 333 patients established the optimal dose range before two subsequent pivotal randomized trials (approximately 300 patients each), including the European Orgalutran Study Group trial discussed above, confirmed efficacy and safety at the selected dose. This is a genuinely rigorous, staged clinical development pathway consistent with standard modern drug development practice. We also want to note that the efficacy gap observed in Ganirelix's pivotal comparison against long-agonist Buserelin has been examined extensively in subsequent research across the reproductive endocrinology field, including meta-analyses comparing antagonist and agonist protocols across many trials and patient populations rather than relying on any single comparative study. This broader body of comparative research has generally continued to find a similar overall pattern — comparable or modestly lower live birth rates with antagonist protocols alongside meaningfully lower OHSS risk — though the magnitude of any efficacy gap has narrowed in some more recent analyses as antagonist protocol timing and adjunct medication strategies have been refined since Ganirelix's original approval trials.

At Verified Peptides, we sell research-grade Ganirelix exclusively for laboratory research, and we think the direct historical comparison between Ganirelix and Cetrorelix (both antagonists, both FDA-approved around the same period, both with substantial independent trial data) offers researchers an unusually well-documented within-class comparison in this catalog.

Ganirelix and Cetrorelix were developed largely independently by competing pharmaceutical companies (Organon and ASTA Medica/Serono respectively) during roughly the same period in the 1990s, both converging on broadly similar general strategies (heavily modified N-terminal region, non-standard amino acids at multiple positions) to achieve GnRH receptor antagonism, illustrating a pattern of largely parallel, independent drug development toward the same therapeutic goal — a pattern also seen among the GnRH agonist analogs (Triptorelin, Leuprolide, Alarelin) profiled elsewhere in this catalog.

The efficacy-versus-safety tradeoff observed between antagonist protocols (like Ganirelix) and long-agonist protocols (like Buserelin, also built in this catalog) in Ganirelix's pivotal trial — somewhat lower pregnancy rates but substantially lower OHSS risk — has been an active area of ongoing clinical research and refinement in reproductive medicine in the decades since these original trials, with more recent research examining modified antagonist protocols and dosing strategies aimed at narrowing this efficacy gap while preserving the safety advantage.

One practical advantage sometimes cited for Ganirelix over Cetrorelix in clinical practice is that Ganirelix is supplied as a premixed, ready-to-use solution, while Cetrorelix (in at least some formulations) requires reconstitution before injection, a formulation-convenience distinction separate from the two compounds' comparable core efficacy and safety profiles.

At Verified Peptides, we require independent third-party HPLC purity testing and mass spectrometry identity confirmation for every batch of research-grade Ganirelix we offer, with a Certificate of Analysis (COA) available for each lot. Given Ganirelix's six distinct modified positions, including the dual homoarginine substitutions unique to this compound among the antagonists in this catalog, identity confirmation is particularly important to distinguish authentic Ganirelix from related but distinct GnRH antagonist analogs.

We source exclusively from manufacturers operating under Good Manufacturing Practice (GMP)-aligned quality systems, and every lot is independently verified rather than accepted solely on a supplier's internal documentation. Researchers should always request and review the specific COA for the lot they receive, confirming purity percentage and molecular identity before use in any experimental protocol, and specifically verifying the presence of both position-6 and position-8 homoarginine modifications, since either being absent would represent a materially different, non-Ganirelix sequence.

Lyophilized Ganirelix is stable when stored at -20°C, protected from light and moisture. At Verified Peptides, we ship lyophilized peptide with appropriate cold-chain packaging to preserve stability in transit.

Once reconstituted, solution should be stored refrigerated at 2–8°C and used within the timeframe indicated on the product's documentation, avoiding repeated freeze-thaw cycles, consistent with standard handling practices for the other GnRH-targeting peptides in this catalog. As with Cetrorelix, Ganirelix's multiple non-standard amino acid substitutions and bulky aromatic side chains may affect aqueous solubility differently than simpler single-substitution peptides, so researchers should follow lot-specific reconstitution guidance rather than assuming identical handling across all peptides in this catalog.