Hormone therapy is used to treat breast cancer that has hormone receptors for estrogen (ER-positive) or progesterone (PR-positive). It works by blocking these hormones, which can slow or stop the growth of cancer cells. Common hormone therapy drugs include tamoxifen and aromatase inhibitors like anastrozole, exemestane, and letrozole. Tamoxifen is often used in both premenopausal and postmenopausal women, while aromatase inhibitors are usually for postmenopausal women. Tamoxifen can also help prevent osteoporosis. However, tamoxifen may increase the risk of uterine cancer, blood clots, stroke, and cataracts. Aromatase inhibitors can lead to osteoporosis and other side effects like hot flashes and joint pain. Other drugs like fulvestrant, toremifene, and targeted therapies such as palbociclib and ribociclib are used for advanced breast cancer. Regular bone density tests are needed to monitor osteoporosis while on aromatase inhibitors. Everolimus can enhance the effectiveness of hormone therapy drugs.