A substance that keeps the testicles and ovaries from making sex hormones by blocking other hormones that are needed to make them. In men, gonadotropin-releasing hormone agonists cause the testicles to stop making testosterone. In women, they cause the ovaries to stop making estrogen and progesterone. Some gonadotropin-releasing hormone agonists are used to treat prostate cancer. Also called GnRH agonist, GnRHa, LH-RH agonist, and luteinizing hormone-releasing hormone agonist.