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Antagon Side Effects

Generic name: ganirelix

Medically reviewed by Last updated on Feb 19, 2024.

Note: This document contains side effect information about ganirelix. Some dosage forms listed on this page may not apply to the brand name Antagon.

Applies to ganirelix: subcutaneous solution.

Serious side effects of Antagon

Along with its needed effects, ganirelix (the active ingredient contained in Antagon) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking ganirelix:

Less common


Incidence not known

Other side effects of Antagon

Some side effects of ganirelix may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

For Healthcare Professionals

Applies to ganirelix: subcutaneous solution.


The more commonly reported adverse reactions have included injection site redness and/or swelling, abdominal pain, and headache; rare postmarketing cases of anaphylaxis have been reported.[Ref]


Among 283 newborns of mothers receiving this drug; 3 neonates had major congenital anomalies (i.e., hydrocephalus/meningocele, omphalocele, and Beckwith-Wiedemann Syndrome) and 18 neonates experienced minor anomalies (i.e., nevus, skin tags, sacral sinus, hemangioma, torticollis/asymmetric skull, talipes, supernumerary digit finger, hip subluxation, torticollis/high palate, occiput/abnormal hand crease, hernia umbilicalis, hernia inguinalis, hydrocele, undescended testis, and hydronephrosis). A subsequent analysis showed the incidence of congenital anomalies with this drug are comparable to another GnRH agonist.

The incidence of congenital malformations after Assisted Reproductive Technology appears to be slightly higher than after spontaneous conception; although this may be related to differences in parental characteristics and higher incidence of multiple gestations.

Common (1% to 10%): Ovarian Hyperstimulation Syndrome, fetal death

Frequency not reported: Congenital anomalies


Common (1% to 10%): Abdominal pain (gynecological), vaginal bleeding[Ref]


Very common (10% or more): Injection site reaction (up to 15%)[Ref]

Following injection, between 10% and 15% of patients reported redness with or without swelling at the injection site. This normally disappeared within 4 hours after administration.[Ref]


During the postmarketing period, rare reports of anaphylaxis (including anaphylactic shock), angioedema, and urticaria have been received, as early as with the first dose.

Postmarketing reports: Hypersensitivity reactions

Nervous system

Common (1% to 10%): Headache[Ref]


Common (1% to 10%): Nausea[Ref]


Uncommon (0.1% to 1%): Malaise[Ref]


Elevated neutrophil counts (8.3 x 10(9)/L or greater) and decreased hematocrit concentrations have been observed during therapy; however, the significance of these findings is not known.

Frequency not reported: Elevated neutrophil counts, decreased hematocrit


Decreased total bilirubin concentrations have been observed during therapy; however, the significance of this finding is not known.

Frequency not reported: Decreased total bilirubin concentrations


1. Cerner Multum, Inc. Australian Product Information.

2. Product Information. Antagon (ganirelix). Organon. 2001;PROD.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.