Doctors may prescribe drugs called gonadotropin-releasing hormone agonists (GnRH agonists) to treat fibroids. Most fibroids shrink by one-third to one-half of their original size after two to three months of treatment with these drugs. Smaller fibroids may cause fewer problems and they are often easier to remove surgically.
Women should not take GnRH agonists for more than six months. After that, the drugs can cause rapid bone loss, leading to osteoporosis. Fibroids generally start to grow again once drug treatment stops. Most women stop having menstrual periods while they are taking GnRH agonists.
What Are GnRH Agonists?
GnRH agonists are drugs that are chemically similar to gonadotropin-releasing hormone (GnRH). This hormone is produced by the hypothalamus, a region in the brain.
GnRH stimulates the release of other hormones from the pituitary gland, a pea-sized gland at the base of the brain. These other hormones areluteinizing hormone and follicle-stimulating hormone. They, in turn, stimulate the ovaries to produce estrogen. GnRH agonists block that process, shutting down estrogen production. Deprived of estrogen, fibroids shrink.
GnRH agonists are approved by the U.S. Food and Drug Administration to treat endometriosis in women and prostate cancer in men. Some are also approved to treat fibroids in women with anemia (low blood count) who are planning to undergo surgery. Names of GnRH agonist drugs include:
How Are GnRH Agonists Used To Treat Fibroids?
Doctors may use these drugs in more than one way to treat fibroids.
If a woman is close to menopause, a doctor may prescribe GnRH agonists for a few months to shrink her fibroids. After menopause, fibroids shrink naturally because estrogen levels in the body decline.
A doctor may prescribe GnRH to shrink fibroids before a woman has surgery. Smaller fibroids may make it possible for a woman to have a vaginal hysterectomy instead of an abdominal one. She may also be able to have laparoscopic surgery, which requires a shorter hospital stay and has a faster recovery time.
What Side Effects Do GnRH Agonists Have?
By blocking estrogen production, GnRH agonists mimic a process that occurs naturally at menopause. The side effects of these drugs are similar to the problems many women have when they go through menopause.
The most common problem (experienced by about 9 out of 10 women) is hot flashes-episodes of suddenly feeling very warm in the face or upper body. During a hot flash, a woman may blush, perspire, or feel her pulse racing. A cold chill may follow the hot flash. Hot flashes are caused by declining or unstable estrogen levels in the body.
Other less common side effects of GnRH agonists include:
irregular vaginal bleeding
thinning of the hair
pain in the bones, joints, and muscles
loss of sex drive
Doctors may also prescribe synthetic hormones to reduce heavy bleeding caused by fibroids. Progestogen is a synthetic version of the female hormone progesterone, which-like estrogen-is made by the ovaries. Androgens (male sex hormones) may also be used to control excessive bleeding caused by fibroids. These synthetic hormones do not shrink fibroids.
Some doctors may prescribe a GnRH agonist in combination with a low dose of estrogen or progestogen. Low doses of these hormones may reduce the side effects of GnRH agonists, which may allow women to be treated safely with these drugs for a longer time.