Drugs designed to produce of the good effects of estrogen (such as osteoporosis or high cholesterol prevention) without increasing cancer risk. They work, like estrogen, by binding to the estrogen receptors on cells in target tissues, such as bone and breast. In some tissues, this binding results in a response similar to that of estrogen, but in other tissues, the binding simply clogs the receptor and prevents the estrogen-associated activity. Thus far, no perfect "designer estrogen" has been developed. Tamoxifen, for example, acts as an antiestrogen in the breast, but shares estrogen's proliferative tendencies in the uterus.