Alendronate is in the group of medicines called bisphosphonates. It alters the cycle of bone formation and breakdown in the body. Alendronate slows bone loss while increasing bone mass, which may prevent bone fractures. Alendronate is used to treat or prevent postmenopausal osteoporosis and steroid-induced osteoporosis. Alendronate is also used to treat Paget's disease of bone.