How Do Antineoplastic GNRH Agonists Work?

Reviewed on 10/25/2021


Antineoplastic gonadotropin-releasing hormone (GnRH) agonists are a class of drugs used to treat advanced prostate cancer, central precocious puberty (a condition causing an early age puberty because of excessive luteinizing hormone [LH] and follicle-stimulating hormone [FSH], resulting in faster than normal bone growth and development of sexual characteristics) in children aged two years and above, endometriosis (abnormal uterine tissue that exists outside of the uterus), and fibroids (benign tumors of the uterus).

GnRH hormone is produced by the hypothalamus (a part of the brain) that further stimulates the pituitary gland to produce LH and FSH. These hormones when released in the blood stimulate the production of testosterone by the testes in men and estrogen by the ovaries in women. The release of GnRH, LH, and FSH is governed by negative feedback, indicating that when too much testosterone or estrogen is produced, the body sends a signal to the pituitary gland to reduce the production of GnRH, which in turn reduces the production of LH and FSH. This results in reduced production of testosterone and estrogen. 

Testosterone promotes the growth of prostate cancer; therefore, GnRH agonists are used to reduce the level of testosterone to slow down the growth of cancer cells. Estrogen promotes the growth of fibroids and areas of endometriosis; therefore, GnRH agonists are used to reduce the production of estrogen, thus treating endometriosis and fibroids.

GnRH agonists are administered as an extended-release (long-acting) suspension to be injected intramuscularly (into the muscle) and subcutaneously (under the skin) once every month and as an implant (a small, thin, flexible tube containing medication) inserted by a doctor on the inside of the upper arm.

GnRH agonists work in the following ways:

  • They work by reducing the amount of testosterone that the body produces which helps in slowing down or halting the growth of cancer cells.
  • They decrease the amount of LH and FSH hormones in the body by stimulating the pituitary gland via a negative feedback mechanism.
  • In addition, they decrease the production of the hormone estradiol (which may stimulate the growth of cancer cells) to levels similar to a postmenopausal state in women.


Antineoplastic GnRH agonists are used to treat conditions such as:

  • Advanced prostate cancer
  • Endometriosis (abnormal uterine tissue that exists outside of the uterus)
  • Uterine leiomyomata (noncancerous growths of the uterus that often appear during childbearing years)
  • Breast cancer 
  • Central precocious puberty (a condition causing an early age puberty because of excessive LH and FSH, resulting in faster than normal bone growth and development of sexual characteristics)


Some of the common side effects include:

  • Nausea
  • Vomiting
  • Constipation
  • Diarrhea
  • Headache
  • Hot flashes
  • Decreased sexual interest
  • Breast tenderness
  • Tiredness/weakness
  • Heartburn
  • Dryness of mouth
  • Increased sweating
  • Loss of appetite
  • Joint/muscle pain
  • Pain, redness, swelling, hardness, or itching at the injection site

Other rare side effects include:

  • Dizziness
  • Depression
  • Fatigue 
  • Chest pain/tightness
  • Anemia (low red blood cell count)
  • Insomnia (trouble falling and/or staying asleep)
  • Shortness of breath
  • Chills, sore throat, fever, or cough
  • Blurred vision
  • Painful or difficult urination
  • Vaginal discharge, dryness, or itching
  • Breast pain or change in breast size in women
  • Unusual weight gain
  • Gynecomastia (breast enlargement in men)
  • Vaginitis (inflammation of the vagina that can result in discharge, itching, and pain)
  • Rash/hives/itching
  • Swelling of the face, eyes, mouth, throat, tongue, or lips
  • Mood swings
  • Peripheral edema (swelling of lower legs or hands)
  • Dysmenorrhea (painful menstruation)
  • Hirsutism (a condition in women causing excessive growth of dark or coarse hair in a male-like pattern)
  • Dyspareunia (painful intercourse)
  • Urinary tract infection

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.



Generic and brand names of antineoplastic GnRH agonists include:


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