Overview Zoladex is an injection used in the treatment of advanced prostate cancer or recurrent prostate cancer after failure of primary treatment. Testosterone feeds prostate cancer (like adding fuel to a fire) and Zoladex acts to stop the production of testosterone . These injections are given every 3-months and is administered in the abdominal wall. A local injection of numbing medicine (Xylocaine) is administered to the site where to Zoladex pellet is inserted into the skin. This pellet dissolves over 12-weeks. Hot flashes may occur.