GnRH agonists and antagonists are two categories of hormone therapy drugs used to stop the growth of uterine fibroids (non-cancerous tumors in the uterus) by controlling estrogen production. Another form of hormone therapy involves the use of oral contraceptives, which also alter natural hormone levels in the body and slow or stop fibroid growth.
Uterine fibroids afflict many women in their late reproductive years. While some fibroids are essentially harmless and never require treatment, others can cause a variety of problems, such as abdominal bloating or discomfort, digestive symptoms, menorrhagia (unusually heavy periods), dysmenorrhea (painful periods), or dyspareunia (pain during sexual intercourse), as well as complications with pregnancy including miscarriage.
The hormone estrogen influences the growth of uterine fibroids, so medications that lower levels of estrogen in the body can help to stop fibroid growth or even shrink fibroids. GnRH agonists and antagonists are two types of medications that can significantly lower estrogen levels. They do this by interfering with the body's ability to process gonadotrophin-releasing hormone (GnRH), the chemical in the body which regulates estrogen and testosterone production. GnRH agonists do this by reducing the number of receptors for GnRH, while GnRH antagonists attach themselves to receptors and prevent actual GnRH from doing the same.
GnRH agonists or antagonists are typically used as a treatment to make fibroids smaller and more controllable before surgery to remove or destroy them. However, the use of these hormonal therapies can cause numerous complications, such as symptoms similar to those experienced as a result of hormonal changes during and after menopause. These include mood swings, changes in metabolism, infertility, pregnancy complications, and osteoporosis (brittle bones). Consequently, GnRH treatments cannot be used during pregnancy or for longer than periods of a few months at a time. Currently, GnRH agonists are used more frequently than GnRH antagonists, but there is some research that suggests the side effects of GnRH antagonists are less problematic than those of GnRH agonists, and antagonists have been found to work more quickly in some comparative trials.
Oral contraceptives or the birth control pill can be used for the control of uterine fibroids, as well. However, instead of blocking the hormone that cues estrogen production, they work by replacing the estrogen and progesterone in the body with slightly altered levels. This generally results in a low enough estrogen level to control fibroid growth.
The side effects of oral contraceptives are similar to those associated with GnRH agonists and antagonists, but less severe. They can include mood swings, changes in metabolism, and, of course, the prevention of pregnancy. Unlike GnRH therapies, however, they can be used for a long period of time without endangering fertility or causing severe enough side effects to require discontinuation of therapy.
After hormonal therapy has been stopped, fibroids tend to regrow, possibly reaching their original size again if the use of hormonal therapy is not accompanied by another treatment such as uterine artery embolization, myolysis, cryomyolysis, laparoscopy, or laparotomy. A medical professional can advise patients on which drug regimens and treatments are preferable, based on the details of each individual case.
Last updated: 06-Jun-07