In recent years, compounds that are structurally similar to the naturally occurring steroids have been examined for their ability to block or substitute for the action of the naturally occurring steroids. On occasion, these substances have both effects, depending on the tissue that is examined or on the physiology of the person receiving the agent. The development of these kinds of compounds, called selective hormone receptor modulators, may provide new treatments that are targeted to specific organs or tissues. One example of these compounds is the selective estrogen receptor modulator raloxifene, which blocks estrogen action at the uterus, and acts like estrogen at the bone, allowing its use in post-menopausal women as estrogen replacement therapy without requiring progesterone.