GnRH Antagonist

A GnRH antagonist is a fertility medicine that helps prevent premature ovulation during ovarian stimulation.

It temporarily reduces pituitary signals that can trigger ovulation, helping the fertility team keep ovulation from happening before eggs are ready for collection. It is usually introduced after stimulation has begun, according to the clinic’s plan.

The medicine acts on gonadotropin-releasing hormone receptors. This gives the treatment team more control over the timing of luteinising hormone release while follicles grow. It does not make eggs or embryos by itself. Its purpose is timing: it helps coordinate stimulation, monitoring, the trigger medicine, and egg collection.

A GnRH antagonist is used in some ovarian stimulation plans, including cycles where several follicles are developed for egg collection. The clinic uses ultrasound findings and hormone results to decide when it is needed. Read more about [Ovarian Stimulation](/treatments/fertility-and-assisted-reproduction/ovarian-stimulation/) and how medicines can fit into a monitored cycle.

A fertility specialist may choose a different suppression approach, change the timing of medicines, or use a cycle plan that does not require the same type of antagonist. The choice depends on ovarian response, the treatment goal, previous cycle information, and the clinic’s protocol. Do not swap or delay doses without direct instructions.

You may be asked to inject the medicine at a particular time each day and attend monitoring appointments. Mild injection-site irritation, headache, nausea, or abdominal discomfort can occur, but symptoms vary. Contact the fertility team promptly for severe pain, marked bloating, breathing difficulty, faintness, or reduced urination, especially during stimulation.

This medicine is generally used for a limited part of one treatment cycle rather than as a long-term medicine. Use the exact preparation, dose, and schedule supplied by the clinic. Tell the team about allergies, current medicines, and any new symptoms. Safe use depends on personalised monitoring and following the instructions for storage and injection.