nafarelin, Synarel

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What is nafarelin, and how does it work (mechanism of action)?

Nafarelin is a synthetic (man-made) protein that blocks the effects of the natural gonadotropin-releasing hormone (GnRH), a hormone that regulates the output of gonadotropins (a class of hormones) by the pituitary gland (a small gland located at the base of the brain). Gonadotropins (follicle stimulating hormone or FSH and luteinizing hormone or LH) are hormones that cause estrogen production by the ovaries. When nafarelin (known scientifically as a GnRH analog) is administered continuously to women in their reproductive years, the pituitary output of FSH, LH, and the production of estrogen by the ovaries are suppressed. Suppression of estrogen production causes menstruation to stop, resulting in a temporary (but reversible) state of "menopause." This temporary  state of menopause results in shrinkage of the lining of the uterus, known as the endometrium.

Endometriosis is a condition whereby the cells that normally form the endometrium inside of the uterus are instead found outside of the uterus. These abnormally located cells (called endometrial implants) are most commonly found on the ovaries, Fallopian tubes, outer surfaces of the uterus or intestines, and on the surface lining of the pelvic cavity. Like the normal endometrium, implants respond to the hormones of the menstrual cycle, i.e., they build up during the month, then break down and bleed during menstruation. However, unlike normal endometrium, the implants bleed internally. (blood from implants cannot exit the body like blood from the uterus can.) The internal bleeding, followed by tissue inflammation and subsequent scarring, is believed to be responsible for the symptoms of pain and infertility in women with endometriosis. Nafarelin has been found to be effective in relieving the pain of endometriosis and shrinking the endometrial implants.

FSH and LH also control the onset of puberty in boys and girls. Therefore, administration of nafarelin blocks the puberty-promoting effects of FSH and LH, reducing the development of secondary sexual characteristics (such as pubic hair) and skeletal development in boys and girls with abnormally early puberty (central precocious puberty) due to problems in the brain that result in high levels of FSH and LH. The FDA approved nafarelin in February 1991.

What brand names are available for nafarelin?


Is nafarelin available as a generic drug?


Do I need a prescription for nafarelin?


What are the side effects of nafarelin?

Side effects of nafarelin are mostly related to the low estrogen state. Common side effects include:

Other important side effects include:

  • acne,
  • muscle pain,
  • reduced breast size, and
  • irritation of the tissue inside the nose.

These side effects should disappear after stopping the medication.

The low estrogen state and the temporary menopause induced by nafarelin can cause a small amount of bone thinning, which may only partially recover after stopping treatment. Patients should discuss this possibility with their doctors and alert their doctors to conditions that they may have that could increase the risk of bone thinning. These conditions include chronic tobacco use, excessive use of alcohol, family history of osteoporosis, and taking other medications that can cause bone thinning (such as anticonvulsants or corticosteroids).

Medically Reviewed by a Doctor on 7/9/2015

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Endometriosis Symptoms, Stages, Treatment
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