Osteoporosis is the primary cause of bone fractures in the elderly, reflecting an imbalance between osteoclasts, bone-degrading cells, and osteoblasts, bone-building cells. Teriparatide is the only FDA-approved treatment for osteoporosis that increases osteoblast activity and lifespan. Medical researchers now report that teriperatide treatment also stimulates the formation of new osteoblasts. However, their findings also show that unexpected adverse effects can develop after treatment stops.