Actonel (risedronate) is in a group of medicines called bisphosphonates (bis FOS fo nayts). Risedronate alters the cycle of bone formation and breakdown in the body. Actonel slows bone loss while increasing bone mass, which may prevent bone fractures. Actonel is used to treat or prevent osteoporosis. Actonel is also used to treat Paget's disease of bone.