Breast cancer is the leading cause of death among women, and its treatment often involves chemotherapy and hormone therapy, which can compromise bone mineral density (BMD). Tamoxifen, a selective estrogen receptor modulator, has different effects depending on the patient's hormonal status. On the one hand, in postmenopausal women, it has a protective effect on BMD; on the other hand, in premenopausal women, it can accelerate bone loss, increasing the risk of osteoporosis and fractures. The reduction in estrogen levels during treatment is a key factor in this bone loss. This review underscores the importance of early risk assessment and regular monitoring of bone mineral density, along with the adoption of individualized pharmacological and non-pharmacological strategies, such as calcium and vitamin D supplementation and physical exercise, to preserve bone health in premenopausal women with breast cancer undergoing endocrine therapy.