A substance that blocks the pituitary gland from making hormones called follicle-stimulating hormone (FSH) and luteinizing hormone (LH). In men, this causes the testicles to stop making testosterone. In women, this causes the ovaries to stop making estrogen and progesterone. Some gonadotropin-releasing hormone antagonists are used to treat advanced prostate cancer. They are also used to treat certain gynecologic conditions and are being studied in the treatment of hormone-sensitive breast cancer. Also called GnRH antagonist, LH-RH antagonist, and luteinizing hormone-releasing hormone antagonist.