Compounds that are similar to naturally occurring hormones have been synthesized and studied for their ability to block or simulate the action of sex steroids such as estrogen and progesterone. The development of this class of compounds, called selective hormone receptor modulators, may provide new treatments that are targeted to specific organs or tissues. One example is the selective estrogen receptor modulator raloxifene, which blocks estrogen action at the uterus, and acts like estrogen at the bone. Raloxifene has been approved for use in post-menopausal women as a form of hormone replacement therapy and a treatment for osteoporosis. It provides many of estrogen's benefits without stimulating the uterine lining and thus may be taken without a progestin.