Luteinizing hormone-releasing hormone (LHRH) agonists (also called LHRH analogs or GnRH agonists) are drugs that lower the amount of testosterone made by the testicles. Treatment with these drugs is sometimes called chemical castration or medical castration because they lower androgen levels just as well as orchiectomy.
Even though LHRH agonists cost more than orchiectomy and require more frequent doctor visits, most men choose this method. These drugs allow the testicles to remain in place, but the testicles will shrink over time, and they may even become too small to feel.
LHRH agonists are injected or placed as small implants under the skin. Depending on the drug used, they are given anywhere from once a month up to once a year. The LHRH agonists available in the United States include:
Leuprolide (Lupron, Eligard)
When LHRH agonists are first given, testosterone levels go up briefly before falling to very low levels. This effect is called flare and results from the complex way in which these drugs work. Men whose cancer has spread to the bones may have bone pain. If the cancer has spread to the spine, even a short-term increase in tumor growth as a result of the flare could press on the spinal cord and cause pain or paralysis. Flare can be avoided by giving drugs called anti-androgens (discussed below) for a few weeks when starting treatment with LHRH agonists.