Gonadotropin Releasing Hormone (GnRH) Agonists

The gonadotropin releasing hormoneinfo-icon agonists, or GnRH agonists, are a class of injectable medicines offered to pre- and perimenopausalinfo-icon women with breast cancer in order to temporarily suppress, or slow, ovarianinfo-icon function. For some women, GnRH agonists are a part of long-term hormonal therapyinfo-icon for breast cancer. When given during chemotherapyinfo-icon these medicines also may protect future fertilityinfo-icon.

Ask your doctors to be specific about what kind of ovarian suppressioninfo-icon they recommend. Ovarian suppression can involve GnRH agonist medicines or oophorectomyinfo-icon, surgeryinfo-icon that permanently removes your ovaries.

Common GnRH agonists are:

  • Goserelininfo-icon (Zoladex)
  • Leuprolide (Lupron)
  • Triptorelin (Trelstar)

How GnRH Agonists Work

In premenopausalinfo-icon women, the brain tells the ovaries to develop an egg, called an oocyte, to be released every month. We call the release of the egg ovulationinfo-icon.   

Before ovulation, the cells around the developing egg make estrogeninfo-icon. After ovulation, these cells make both estrogen and progesteroneinfo-icon.

GnRH agonists tell the brain not to signal the ovaries to develop an egg. Stopping the brain’s signal means that the ovaries do not develop an egg, ovulation does not occur, and estrogen and progesterone are not made.

When the ovaries stop making as much estrogen, breast cancer cells that are estrogen receptor-positiveinfo-icon can’t continue to grow.

Who Gets GnRH Agonists

GnRH agonists are used in two ways:

Women with estrogen receptor-positive breast cancer who are pre- or perimenopausalinfo-icon may be given GnRH agonists along with tamoxifeninfo-icon or another hormonal therapyinfo-icon to treat breast cancer, depending on the stageinfo-icon of the cancer. Once your ovaries are fully suppressed, your doctor might switch you from tamoxifen to an aromatase inhibitorinfo-icon.

Women getting chemotherapy treatment may also be given GnRH agonists in order to protect future fertility.

How GnRH Agonists Are Given

  • Goserelininfo-icon is given by injectioninfo-icon once a month or once every 3 months
  • Leuprolide is given by injection once a month or once every 3 months
  • Triptorelin is given by injection once a month

Side Effects and Things to Remember

The GnRH agonists may cause a variety of side effects related to low estrogeninfo-icon levels. Remember to talk to your healthcare team about any side effects you may experience, including:

After you finish taking a GnRH agonist, your brain will return to signaling your ovaries to start working again, but it may take some time.

Your doctor, pharmacistinfo-icon or nurseinfo-icon can help you manage your side effects. You can also go to our section on Side Effects for more information.

October 7, 2019
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