There is little difference between imported and domestic letrozole side effects, and common ones include malaise, night sweats, fatigue, nausea, and high blood pressure. Common adverse reactions to Letrozole include weight change, malaise, fatigue, night sweats, hot flashes, anorexia, constipation, vomiting, edema, nausea, hypertension, dizziness, osteoporosis, hypercholesterolemia, arthralgia, pain in the extremities, dorsalgia myalgia, ovarian cysts, vaginal bleeding, and hair loss. Serious adverse reactions include heart failure, myocardial ischemia, myocardial infarction, bone fracture, cataract, endometrial hyperplasia, and endometrial cancer. Letrozole is primarily used in the adjuvant treatment of postmenopausal patients with early breast cancer, in the adjuvant treatment of postmenopausal patients with early breast cancer who have been receiving adjuvant tamoxifen for five years, and in the treatment of postmenopausal patients with advanced breast cancer who are estrogen and progesterone receptor-positive or whose receptor status is unclear. It is contraindicated in pregnant women and patients with hypersensitivity reactions to the product. Letrozole should be used in strict compliance with medical advice and standardized use to avoid adverse consequences.