Ganirelix is a gonadotropin-releasing hormone receptor (GnRH) antagonist that is used to prevent premature ovulation when a woman undergoes fertility treatments, including in vitro fertilization (IVF).

Endometriosis can reduce fertility, and some women can only become pregnant with the help of IVF. The technique involves hormone treatments to mature several eggs at the same time (hyperovulation). GnRH agonists or antagonists are administered in conjunction with an ovarian hyperstimulation protocol to prevent the ovulation of eggs that are too immature to be used for IVF.

For endometriosis patients, GnRH antagonists are preferred over GnRH agonists as a conjunctive treatment for ovarian hyperstimulation because they do not cause flare phases.

How ganirelix works

GnRH acts by binding to GnRH receptors, which leads to the production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These two hormones stimulate the ovaries to mature and release eggs. GnRH agonists and antagonists both suppress LH and FSH, and thereby help prevent premature ovulation during ovarian hyperstimulation, but they differ in the way they work.

While GnRH antagonists block GnRH receptors (which leads to a suppression of LH and FSH), GnRH agonists bind and activate these receptors, initially stimulating the release of the two hormones. However, because GnRH agonists bind much stronger to the receptors, the receptors soon become resistant to the stimulus. Without signals from the GnRH receptors, LH and FSH release is suspended.

LH and FSH also control the levels of estrogen, a hormone that can stimulate the growth of endometriotic lesions. Because GnRH agonists stimulate a temporary LH and FSH release, they can cause a flare phase in endometriosis patients. For this reason, GnRH antagonists such as ganirelix are preferred over GnRH agonists to treat patients with endometriosis.

Ganirelix in clinical trials

A study assessed whether ganirelix affects the endometrial thickness of regularly menstruating women. A total of 35 women were studied for two menstrual cycles. During the first cycle, the participants received no treatment, and during the second cycle, they received 25 mg of ganirelix per day for three days via subcutaneous (under-the-skin) injection. The endometrial thickness did not differ in the control and ganirelix-treated cycles, suggesting that ganirelix has no effect on the thickness of the endometrium.

An open-label clinical trial (NCT03746535) aims to assess whether ganirelix treatment increases the risk of cardiovascular disease. Women with endometriosis are suspected of having an increased risk for cardiovascular disease because they tend to have elevated levels of inflammation and endothelial dysfunction.

Endothelial dysfunction can contribute to the development of cardiovascular disease because endothelial cells line the inner wall of blood vessels and play an essential role in the regulation of blood pressure, and high blood pressure is associated with cardiovascular disease.

Estrogen suppression may increase the risk of cardiovascular disease and, because GnRH antagonists decrease estrogen levels, ganirelix may have an impact on this risk in patients with endometriosis. To assess cardiovascular disease risk of women in the trial, the dilation of microvessels (small blood vessels) in their skin, and the velocity of their blood flow will be measured.

The trial is not yet recruiting. Up-to-date information can be found on


Last updated: August 5, 2019


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