Endometriosis is a condition where endometriotic tissue, which usually lines the uterus, grows elsewhere in the body forming lesions. With each menstrual cycle, these lesions thicken and break down. However, unlike the tissue in the uterus that exits the body during menstruation, these lesions have no safe route to leave the body. This leads to endometriosis-associated symptoms such as pain and infertility.
There is currently no cure for endometriosis, but there are several treatments available to manage the symptoms of the condition. Hormonal therapy is one option. These medications interfere with the menstrual cycle and reduce the thickening of endometrial lesions. There are several hormonal therapies that work by different mechanisms, including gonadotropin-releasing hormone (GnRH) receptor agonists.
How GnRH receptor agonists work
GnRH regulates the production of hormones that control the menstrual cycle, such as estrogen. It acts by binding to GnRH receptors in the pituitary gland. GnRH receptor agonists bind to the same receptors and initially cause an increase in estrogen production, which may temporarily worsen symptoms. But because GnRH agonists bind much stronger to the receptors than GnRH does, the receptors soon become resistant to the hormone and no longer react to the stimulus. As a consequence, estrogen synthesis by the ovaries is suppressed, and the menstrual cycle is suspended.
Estrogen is involved in the thickening of endometriotic tissue during the menstrual cycle. In endometriosis, the hormone also stimulates the growth of endometriotic lesions outside the uterus. By reducing estrogen levels, GnRH receptor agonists inhibit the growth of these lesions and endometriosis-associated symptoms.
GnRH receptor agonists for endometriosis
Lupron Depot (leuprolide acetate) is a GnRH receptor agonist approved by the U.S. Food and Drug Administration in 1990. Clinical trials have shown that Lupron Depot reduces pain in endometriosis patients. Studies have also shown that the medication in combination with an add-back therapy causes fewer side effects.
Zoladex (goserelin acetate) is an FDA-approved implant injected every month under the skin that gradually dissolves and releases the medication. Clinical trials have shown that Zoladex reduces the growth of endometriotic lesions and pelvic pain.
Synarel (nafarelin) is an FDA-approved medication for endometriosis that is administered via a nasal spray pump. Clinical trials have shown that Synarel reduces endometriosis symptoms, such as dysmenorrhea (painful periods), dyspareunia (painful intercourse), and pelvic pain.
Triptorelin, sold under the brand names of Gonapeptyl, Decapeptyl, and Trelstar among others, comes as an injectable suspension. Studies have shown that triptorelin improves endometriosis pain symptoms and reduces the volume of endometriotic lesions.
GnRH receptor agonists cause bone thinning. For this reason, they should not be taken for longer than six months. An add-back therapy with a low dose of estrogen or progesterone taken alongside a GnRH receptor agonist helps maintain healthy bones and reduce menopause-like symptoms associated with low levels of estrogen.
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