Overview of GnRH Antagonists Used in IVF Treatments

Woman lying in bed with abdmonial cramps and headache, possible side effects of Ganirelix
The most common side effects of GnRH antagonists like Ganirelix are abdominal tenderness and headache. AnaBGD / iStock Photo

GnRH antagonists are injectable medications used during IVF treatment. They prevent premature ovulation so your doctor will be able to retrieve eggs from your ovaries before they are released and “lost.”

Don’t confuse GnRH antagonists with GnRH agonists (like Lupron.) GnRH agonists cause a surge in reproductive hormones for a few days and then shut down those hormones. When used during IVF treatment, they need to be started at least a couple of weeks before the IVF treatment cycle begins.

GnRH antagonists do not create this initial surge in hormones. They are started after the IVF cycle has begun and may be taken only once or daily for a few days.

Types of GnRH Antagonists

There are two basic GnRH antagonists on the market: Antagon (ganirelix acetate) and Cetrotide (cetrorelix.)

These medications are taken via injection. Treatment may involve one injection, daily injections over several days, or single injections are taken a few days apart. It all depends on your particular IVF treatment plan.

GnRH antagonists are slightly more expensive than GnRH agonists, but the additional cost may not make a big impact since antagonists are taken for a shorter period of time. Also, some women believe the fewer side effects are worth the additional costs.

Some fertility doctors prefer GnRH agonists because they have been in use longer. Research has shown conflicting results regarding pregnancy success rates with GnRH agonists compared to antagonists. Talk to your doctor before deciding on a treatment option.

Side Effects of GnRH Antagonists

Cetrorelix and ganirelix acetate both work by shutting down the pituitary gland’s ability to produce and release follicle stimulating hormone (FSH) and luteinizing hormone (LH).

The shutdown induces a state of temporary menopause, which may come with side effects. The side effects you experience usually depends on how long you are taking the medication.

Not all possible side effects and risks are included in the list below. If you are taking a GnRH antagonist and have severe side effects, unusual symptoms, or are concerned for any reason, contact your doctor.

Common side effects of cetrorelix (Cetrotide) include:

  • Abdominal pain and tenderness
  • Headache
  • Itching and a rash that looks like hives at the site of the injection, which lasts up to two hours but not long-term (this is not an allergic reaction, but a normal side effect)
  • Nausea

Common side effects of ganirelix acetate (Antagon) include:

  • Headache
  • Hot flashes
  • Injection site pain or redness
  • Nausea
  • Stomach ache

Risks of GnRH Antagonists

As with any medication or treatment, there are risks of taking GnRH antagonists. Discuss the pros and cons with your doctor, as they can help you weigh the risks and benefits.

  • Birth defects: Studies have found a slightly higher risk of birth defects in a pregnancy conceived while taking ganirelix acetate. Whether this is connected to this particular medication, other IVF drugs, the IVF procedures themselves, or infertility is unknown.
  • Fetal death: During clinical studies, 4% of pregnancies conceived while taking GnRH antagonists ended in fetal death.
  • Ovarian hyperstimulation syndrome (OHSS): One 2019 study of 2572 cycles found a higher rate of moderate to severe OHSS among patients who were treated with ganirelix acetate vs. cetrorelix. Studies have found that the risk of developing OHSS is slightly lower with GnRN antagonists when compared to treatment with GnRH agonists.
  • Severe OHSS. Occurs in less than 1% of patients. Contact your doctor immediately if you experience difficulty breathing, vomiting, severe abdominal or pelvic pain, sudden weight gain, or severe bloating. 
6 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Grow D, Kawwass J, et al. GnRH agonist and GnRH antagonist protocols: comparison of outcomes among goodprognosis patients using national surveillance data. Reprod. BioMed. Online. 2014;29:299–304. doi:10.1016/j.rbmo.2014.05.007

  2. Society for Assisted Reproductive Technology. GnRH antagonist therapy.

  3. Memorial Sloan Kettering Cancer Center. Cetrorelix.

  4. Cleveland Clinic. Ganirelix injection.

  5. Zhang J, Zhou X, Chen Y, et al. Effects of cetrorelix versus ganirelix in gonadotropin-releasing hormone antagonist cycles for preventing premature luteinizing hormone surges and on clinical outcomes of IVF-ET cycles. Nan Fang Yi Ke Da Xue Xue Bao. 2019;39(10):1207-1212. doi:10.12122/j.issn.1673-4254.2019.10.12

  6. Cleveland Clinic. Ovarian hyperstimulation syndrome (OHSS).

By Rachel Gurevich, RN
Rachel Gurevich is a fertility advocate, author, and recipient of The Hope Award for Achievement, from Resolve: The National Infertility Association. She is a professional member of the Association of Health Care Journalists and has been writing about women’s health since 2001. Rachel uses her own experiences with infertility to write compassionate, practical, and supportive articles.