Ganirelix is a synthetic GnRH antagonist decapeptide (MW ~1570.4 g/mol) FDA-approved for the prevention of premature LH surges during controlled ovarian hyperstimulation in women undergoing assisted reproductive technology (ART) procedures. As a GnRH antagonist, it provides immediate suppression of gonadotropins without the initial flare characteristic of GnRH agonists, allowing for shorter and more flexible IVF stimulation protocols. Ganirelix is administered as a daily subcutaneous injection during the late follicular phase of stimulation.
Category: Reproductive / Hormonal. Evidence rating: A (strong human clinical data).
Clinical status: FDA-approved (Ganirelix Acetate Injection for prevention of premature LH surges in IVF, 1999)
Ganirelix competitively blocks GnRH receptors on pituitary gonadotrophs, immediately suppressing LH and FSH secretion without an initial stimulatory phase. This direct antagonism prevents premature LH surges that could cause premature ovulation during controlled ovarian hyperstimulation, which…
Safety considerations: Injection site reactions (redness, swelling, bruising) in approximately 12% of patients; Abdominal pain (4.8%); Headache (3%).
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-08-12.
Related peptides: Kisspeptin, Gonadorelin, Oxytocin.
Compare: Ganirelix vs Kisspeptin, Ganirelix vs Gonadorelin, Ganirelix vs Oxytocin.
Ganirelix immediately blocks GnRH receptors, preventing premature LH surges without causing an initial hormonal flare. This allows it to be started in the mid-follicular phase (typically stimulation day 5-6), shortening the overall IVF protocol by about a week compared to GnRH agonist long protocols. It also significantly reduces the risk of ovarian hyperstimulation syndrome.
Ganirelix is typically started on day 5 or 6 of gonadotropin stimulation, or when the lead follicle reaches approximately 14 mm. It is continued daily until the day of hCG or GnRH agonist trigger for final oocyte maturation, usually for 4-5 days.
Ganirelix and cetrorelix are both GnRH antagonists used in IVF with similar efficacy and safety profiles. The choice is often based on local availability, cost, and physician preference. Both are administered as daily 0.25 mg subcutaneous injections during controlled ovarian stimulation.