A gonadotropin-releasing hormone (GnRH) antagonist is a medicine used during ovarian stimulation to prevent a premature LH surge, which could otherwise trigger ovulation before eggs are ready for retrieval. Unlike a GnRH agonist, it acts rapidly by directly blocking the pituitary gland's receptors, and is typically used for a shorter part of the stimulation cycle in what is often called the 'antagonist protocol'. The antagonist protocol is commonly used in Indian IVF practice, including for women considered at higher risk of ovarian hyperstimulation syndrome (OHSS), because it allows the option of an alternative trigger approach. The treating clinic decides when to start the antagonist and monitors the response with scans and blood tests; patients should not alter timing without clinic guidance. As a prescription-only medicine in India, its use is regulated by the Central Drugs Standard Control Organisation (CDSCO).
Also known as: antagonist protocol injection
Related India guides
Sources
- ICMR Standard Treatment Workflows (icmr.gov.in/standard-treatment-workflows-stws)
- Central Drugs Standard Control Organisation (cdsco.gov.in)
Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.