Synarel, a nasal spray, is approved by the U.S. Food and Drug Administration (FDA) to manage both endometriosis and its symptoms in women ages 18 or older. A hormonal treatment, it works to reduce the size of endometrial lesions and to ease symptoms associated with the disease, such as chronic pelvic pain, dysmenorrhea (painful periods), and dyspareunia (painful intercourse).

Synarel is also used to treat precocious puberty in both boys and girls.

How Synarel works

Synarel contains an active component called nafarelin acetate, which is a synthetic analog of the naturally occurring gonadotropin-releasing hormone (GnRH). This hormone controls the production of sex hormones, such as estrogen, so as to help regulate fertility, the menstrual cycle, and sexual development during puberty.

In endometriosis, tissue resembling the endometrium — the lining of the uterus — starts to grow elsewhere, usually in the pelvic region, forming lesions. These lesions respond to hormonal cycles in the same way as the endometrium, and swell and shed each month. However, because there is no safe route for them to leave the body, they cause inflammation and pain.

Synarel works to inhibit the menstrual cycle by lowering the levels of hormones made by the ovaries, including estrogen.

Upon inhalation, Synarel binds to the GnRH receptor located on the pituitary gland, initially causing the release of hormones – follicle stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH stimulate the production of female sex hormones such as estrogen.

Prolonged stimulation of the GnRH receptor by Synarel desensitizes the receptor, however, which then lowers the levels of LH and FSH released, which subsequently lead to lower levels of estrogen. This stops the menstrual cycle, inducing a temporary and reversible menopausal-like state, to lessen the pain associated with endometriosis.

Synarel in clinical trials

Clinical studies have shown that Synarel is comparable to danazol in relieving the symptoms of endometriosis and in reducing the size of endometrial lesions. (Danazol is a synthetic androgen, and has been used to treat endometriosis since the ’70s).

A controlled clinical trial found that intranasal Synarel was comparable to Lupron Depot injected into the muscle for treating pain and lesions caused by endometriosis.

Other Information

Since Synarel lowers the estrogen level in the body, it commonly causes side effects similar to those of menopause. These include hot flashes, moodiness, acne, vaginal dryness, headache, and decreased interest in sex.

Synarel should not be administered to patients who are pregnant, breastfeeding, have undiagnosed abnormal vaginal bleeding, or are allergic to any components in Synarel.


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