The bones in people taking the drugs were showing microscopic cracks, researchers at Imperial College London discovered when they examined patients who had suffered a hip fracture.
Bisphosphonates are designed to slow the body's processes of removing ageing or damaged bone—but doctors have been concerned that patients were still suffering fractures even after taking the drugs a long time.
The researchers took samples from 16 hip-fracture patients who had been taking the drugs and compared them to samples from people of a similar age but who weren't prescribed bisphosphonates.
The bone samples from those taking the drugs were showing cracks that made the bones more fragile and liable to fracture.
The drugs are routinely given to treat osteoporosis and bone loss from chemotherapy in cancer patients.