What is a GnRH Agonist?

A GnRH agonist, or gonadotropin-releasing hormone agonist, is a class of medication used to help control certain hormones naturally secreted by the body. The hormones affected by these medications are usually those related to puberty and reproduction. Medications in this class may be used to help treat a variety of conditions, including endometriosis, premature puberty, and prostate cancer. Health-care providers often caution against a number of possible, and sometimes serious, side effects and recommend against the use of a GnRH agonist in certain people.

In general, a GnRH agonist is used when the desired end result is to reduce the amount of reproductive hormones circulating in the body. Medications in this class typically work by forcing the body’s pituitary gland to first overproduce follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which both play a role in the body’s production of estrogen and testosterone. Over time, this causes the pituitary to exhaust its normal supply of FSH and LH, which then results in lowered levels of these hormones, as well as estrogen and testosterone, in the body.

Due to this mechanism of action, a GnRH agonist may be used in the treatment of certain conditions that are related to hormonal levels. In women, such conditions can include fibroids and endometriosis. These are both conditions related to tissue growth in the uterus, which is often stimulated by the presence of estrogen. By reducing the amount of estrogen circulating in a woman’s body, the medication may help prevent the abnormal tissue growth that is associated with these conditions, thereby helping to relieve symptoms.

A GnRH agonist may also be used in both males and females to treat premature puberty, a condition that results when the pituitary begins producing reproductive hormones too early. By slowing or shutting down production of these hormones, the agonist may help delay full puberty progression. In adult men with advanced prostate cancer, a GnRH agonist can also be used to help lower testosterone levels, which can be beneficial in stopping or slowing the growth of abnormal prostate tissue.

Health-care providers often warn patients about a variety of possible side effects associated with the use of a GnRH agonist. Since drugs in this class over-stimulate hormone production at first, people may experience worsening symptoms at the start of treatment. Such symptoms can include increased pain and bleeding in women with endometriosis and increased urinary symptoms in men with prostate cancer. These side effects often resolve after an initial period, once hormone levels begin to lower.

Longer-lasting side effects can include loss of sex drive, hot flashes, and loss of bone mass. Some studies have shown that men with prostate cancer who are treated with a GnRH agonist may be at higher risk for certain serious side effects, such as heart attack, diabetes, and stroke. Due to their effects on hormones and the reproductive system, these medications are generally contraindicated in women who are breastfeeding, pregnant, or trying to become pregnant.