Estrogen protects women's bones, but estrogen levels decline during menopause, which can lead to rapid bone loss and osteoporosis. Osteoporosis causes bones to become weak and brittle, increasing the risk of fractures, especially in the hip, spine and wrist. Hormone therapy is one treatment for osteoporosis and menopause symptoms, but it can have side effects, as can bisphosphonate drugs like Fosamax that are also used to treat osteoporosis.