A halogenated derivative of 17-alpha-methyltestosterone. Similar to testosterone, fluoxymesterone binds to and activates specific nuclear receptors, resulting in an increase in protein anabolism, a decrease in amino acid catabolism, and retention of nitrogen, potassium, and phosphorus. This agent also may competitively inhibit prolactin receptors and estrogen receptors, thereby inhibiting the growth of hormone-dependent tumor lines. Fluoxymesterone is approximately five times more potent than methyltestosterone.