Gonadotrophin-releasing Hormone (GnRH) Analogue Injections

for the Treatment of Pelvic Pain & Fibroids (Decapeptyl / Zoladex)

Obstetrics & Gynaecology

What are GnRH analogues?

GnRH analogue is a modified version of a hormone produced naturally by your body.

GnRH analogues are designed to ‘switch off’ the ovaries temporarily and create a ‘menopausal’ state. This is done by blocking the hormones that stimulate the ovaries to produce eggs and will only last as long as you are on the medication.

Examples of the GnRH given in this treatment include Decapeptyl (triptorelin acetate), Zoladex (gosarelin acetate) and Prostap (leuprorelin acetate).

What are GnRH analogues used for?

GnRH analogues are offered to patients with gynaecological conditions that are affected by the hormones of the menstrual cycle.

These include:

  • Endometriosis, adenomyosis and pelvic pain - to reduce pain related to the menstrual cycle and heavy periods.
  • Fibroids - to reduce symptoms such as heavy periods, or as a longer term treatment if surgery is not an option.
  • Given before surgery such as fibroid removal or endometrial ablation - to make fibroids smaller and/or the endometrial lining thinner making them easier and safer to remove or treat. It will also give an indication to how you may feel following surgery.
  • As a diagnostic test - to see if conditions such as severe pre-menstrual syndrome (PMS) or chronic pain are affected by hormones of the menstrual cycle, giving us a better idea how to manage the pain. If the GnRH analogues are unsuccessful, the removal of the ovaries will also be unsuccessful.

How do I take GnRH analogues?

GnRH analogues are usually given as an injection into a muscle such as the buttocks.

This may be a one-off injection or a course of injections (for example, once a month for 6 months).

You will have your first injection at the hospital and any further injections will be with your GP or practice nurse. Some preparations are also available as a nasal spray.

How long can I stay on GnRH analogues for?

Currently, GnRH analogues are not licensed for use for more than 6 months due to concerns that the treatment causes thinning of the bones. In some cases, a Consultant Gynaecologist can agree to a more prolonged course of treatment however, you must be made aware of the risks. You should also be advised to have bone scans along with hormone replacement therapy (HRT).

Are there any other risks or side effects with GnRH analogues?

As with most medications, GnRH analogues may produce unwanted side effects.

Very common (may affect more than 1 in 10 people)

  • difficulty sleeping
  • headaches
  • acne
  • hot flushes
  • sweating

Common (may affect up to 1 in 10 people)

  • weight changes
  • mood changes
  • depression
  • tingling in hands or feet
  • dizziness
  • nausea
  • joint pain
  • muscle weakness
  • breast tenderness
  • changes in breast size
  • vaginal dryness
  • swelling in ankles
  • skin reactions at the injection site (these include skin hardening, redness, pain, abscesses, swelling, nodules, ulcers, and skin damage)

Uncommon (may affect up to 1 in 100 people)

  • loss of appetite
  • changes in blood lipids (cholesterol)
  • altered vision
  • pounding heartbeats
  • diarrhoea
  • vomiting
  • abnormalities in liver blood tests
  • hair loss
  • muscle aches
  • fever
  • chills
  • tiredness

Frequency not known (how often they occur cannot be estimated from the available data) 

  • blood tests may show anaemia (low red cell counts), low counts in white cells or platelets, changes in blood sugar
  • paralysis
  • blood clots in the lungs
  • high or low blood pressure
  • jaundice
  • abnormalities in liver function
  • fracture of the spine
  • seizure
  • thinning of bone
  • vaginal bleeding
  • inflammation of lungs or lung disease

These side effects are reversible and, in most cases, will stop when the treatment ends. You may be prescribed HRT during your treatment to replace what your body would normally be producing and this will reduce these side effects. If the side effect become too much, please contact the clinic for advice.

Allergic reactions

Allergic reactions to GnRH analogues are very uncommon, however, if you experience any of the following please seek medical attention immediately:

  • itching
  • skin rash
  • shortness of breath
  • chest pain

Following your first injection your body may try to compensate by increasing your hormones. This may last for around 2 weeks until your body adjusts to the medication. Your symptoms may feel worse during this time.

The medication will usually stop your periods but you may experience a vaginal bleed during the first month of treatment. This is known as a ‘hormone withdrawal bleed’ and will stop once your body has adjusted to the medication.

Contraception and fertility

You should not have this treatment if you are pregnant, trying to conceive or breastfeeding. You will be asked to provide a urine sample at your appointment to ensure you are not pregnant when the treatment is given.

Although the injections work by stopping the menstrual cycle, it is not licenced as contraception. You should use barrier contraception (e.g. condoms or diaphragm) for the duration of your treatment.

Hormonal contraception must not be used during your treatment.

There is no long-term impact on fertility once the treatment is stopped and the menstrual cycle returns. However, a regular menstrual cycle may take 2-3 months to return. The longer you use - this treatment, the longer it may take for your periods to return to normal.

If you have any further questions you can contact us in the Gynaecology Clinic at Greenoaks, telephone: 01709 427641.

Produced by Mr R Faraj and Dr W Smith (ST5), September 2017. April 2014, April 2020. 
Revised April 2020, July 2022. Revision due July 2024. Version:4.0
©The Rotherham NHS Foundation Trust 2022. All rights reserved.

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