Which class of drugs can function as estrogen receptor agonists or antagonists?

Selective estrogen receptor modulators (SERMs) are a class of drugs that can both activate and inhibit estrogen receptors, depending on the specific tissue involved. This unique dual action allows SERMs to function as estrogen receptor agonists in some tissues, where they mimic estrogen's effects, and as antagonists in others, where they block estrogen's effects.

For example, in breast tissue, SERMs such as tamoxifen act as estrogen antagonists, which can help slow the growth of certain types of breast cancer that rely on estrogen to proliferate. Conversely, in bone tissue, SERMs work as estrogen agonists, helping to maintain bone density and reduce the risk of fractures.

This property of targeting estrogen receptors differently in various tissues makes SERMs valuable in treating hormone-sensitive conditions, particularly in breast cancer, as well as in managing osteoporosis in postmenopausal women.