Why is GnRH agonist used in GnRH analogue therapy?

GnRH is a natural messenger from the brain that guides the release of hormones involved in the menstrual cycle. A GnRH agonist first imitates that messenger. With continued use, the brain's signalling system becomes less responsive, so the ovaries receive less stimulation and oestrogen levels fall for a time.

This temporary low-hormone state may shrink or quiet hormone-responsive tissue, reduce bleeding, or ease symptoms depending on the reason for treatment. The response varies by medicine, dose, timing, and the condition being treated. Read more about the [GnRH Agonist](/materials/gnrh-agonist/) and [GnRH Analogue Therapy](/treatments/medical-gynaecology/gnrh-analogue-therapy/).

Use the medicine on the schedule provided and attend planned reviews. Your clinician may check symptoms, bleeding, hormone effects, or other measures relevant to your condition. Hot flushes, sleep changes, vaginal dryness, mood changes, headache, or an injection-site reaction can occur because hormone levels change.

Keep a note of new symptoms and any bleeding pattern, especially after treatment starts. Do not change the dose, stop early, or add hormonal products without discussing it with the prescribing team.

Contact your care team promptly for heavy or persistent bleeding, severe pelvic pain, marked mood change, or symptoms that are difficult to manage. Seek urgent help for sudden chest pain, trouble breathing, fainting, or swelling and pain in one leg. These symptoms need assessment rather than being assumed to be a routine treatment effect.

Ask which condition the medicine is targeting, how long the hormone-suppressed phase is expected to last, and how your response will be followed. You can also ask which side effects need a same-day call, whether additional treatment is suitable for symptoms, and what to expect when the medicine is stopped.