Endocrine therapy for breast cancer is a very important tool in the comprehensive treatment of breast cancer and is divided into premenopausal and postmenopausal treatment according to the patient’s menstrual status. The main side effects of premenopausal estrogen receptor modulators, including tamoxifen and toremifene, are liver function impairment, and obesity, hot flashes, endometrial thickening and ovarian cysts may occur. In addition, toremifene and tamoxifen may cause menopause during long-term use, which is a normal reaction. Many clinical patients are concerned about endometrial thickening leading to endometrial cancer, but the chances are low and most do not require special treatment. The main side effects of postmenopausal aromatase inhibitors, such as anastrozole, letrozole and exemestane, are for bone loss and cardiovascular disease. In particular, they cause hyperlipidemia when the lipid metabolism is abnormal, which is clinically known as hyperlipidemia. Hyperlipidemia is more harmful to older patients, especially those with hypertension and heart disease, and needs to be taken seriously and treated appropriately with lipid-lowering therapy. In addition, patients may experience increased bone pain, especially stiffness and pain in small joints at the end of the day, which improves in the evening.