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Antagon Side Effects

Generic Name: ganirelix

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

For the Consumer

Applies to ganirelix: subcutaneous solution

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


  • Cough
  • difficulty with swallowing
  • dizziness
  • fast heartbeat
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • shortness of breath
  • skin rash, hives, or itching
  • tightness in the chest
  • unusual tiredness or weakness

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

  • Headache
  • redness, pain, or swelling at the injection site

For Healthcare Professionals

Applies to ganirelix: subcutaneous solution


Genitourinary symptoms of abdominal pain (4.8%), ovarian hyperstimulation (2.4%), and vaginal bleeding (1.8%) have been reported.[Ref]

Nervous system

Nervous systems side effects have been limited to headache in 3% of patients.[Ref]


Local side effects have included non-specific injection site reactions (1.1%).[Ref]


Gastrointestinal side effects of nausea and abdominal pain have occurred in 1.1% and 1% of patients, respectively.[Ref]


Follow-up studies of 282 newborns revealed 3 neonates with major and 18 with minor congenital anomalies. The major anomalies included hydrocephalus/meningocele, omphalocele, and Beckwith-Wiedemann Syndrome. Minor dermal, skeletal, muscular, and organ (angioma, hernia , testes, and renal) anomalies were reported.[Ref]

Neonatal congenital anomalies have been reported. The causal relationship of the anomalies and ganirelix therapy is unknown. Multiple factors may confound assisted reproductive procedures.[Ref]


Hypersensitivity side effects have included postmarketing reports of hypersensitivity reactions, including anaphylactoid reactions with the first dose.


1. "Product Information. Antagon (ganirelix)" Organon, West Orange, NJ.

2. Nelson LR, Fujimoto VY, Jaffe RB, Monroe SE "Suppression of follicular phase pituitary-gonadal function by a potent new gonadotropin-releasing hormone antagonist with reduce histamine-releasing properties (ganirelix)." Fertil Steril 63 (1995): 963-9

3. Gillies PS, Faulds D, Balfour JAB, Perry CM "Ganirelix." Drugs 59 (2000): 107-11

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.