At their best, hospitals are places where doctors bring babies safely into the world and bring gravely ill people back from the brink of death. But at their worst, they are dangerous places where patients are vulnerable to hospital-acquired infections and a host of harmful medical errors. A recent analysis grading more than 2,500 US hospitals on safety gave more than 1,000 of them a C or worse. One way to make hospital care much safer and somewhat less expensive is to reduce the number of medicines people are on when they are in the hospital.