• Dr Peter Chew

What is GnRH agonist?

I am infertile. Recently, I was diagnosed with endometriosis. My gynaecologist suggested treatment with GnRH agonist. Can you explain how the medicine works? Any side effects?

Answer: Endometriosis is a disorder of the female reproductive system in which there is a backflow of the menstrual blood (endometrial tissue) into the pelvic cavity. The endometrial tissue responds to the female sex hormone oestrogen and grows with each menstrual cycle (please refer to “Endometriosis” article on the website under Home > Articles > Gynae Conditions > Endometriosis).

GnRH agonist is a drug modified from the naturally occurring hormone known as gonadotropin releasing hormone (GnRH), which controls the menstrual cycle.

It stops the production of oestrogen by a series of mechanisms. This deprives the endometrial tissues of oestrogen, causing them to shrink and become inactive. This may help the reproductive organs to regain their function and allow the woman to get pregnant after the treatment is stopped.

The usual length of treatment with a GnRH agonist is 3–6 months. You should notice an improvement in your symptoms within 4–8 weeks of treatment. The side effects are largely the result of the low oestrogen in the body. They are usually the symptoms associated with the menopause. Common side effects are:

• Insomnia

• Decreased libido

• Headaches

• Vaginal dryness

• Mood swing

The more serious side effect is thinning of the bones, particularly the bones of the spine. The decrease in bone density is usually about 5% if the treatment is prolonged for more than 6 months. Most of the bone lost during treatment regenerates within 6 months of completing treatment.

GnRH agonist has been used to treat women with endometriosis for over 20 years. It is safe, effective and generally well tolerated when used in combination with add-back therapy which involves taking a low-dose oestrogen. This reduces the menopausal symptoms and prevents or minimises the thinning of the bones.

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