For years, advocates, researchers and government officials have worried about the overuse of antipsychotic medications that can put elderly patients into a stupor and increase their risk of life-threatening falls. A national initiative helped reduce the use of such drugs among long-term nursing home residents by 20 percent between the end of 2011 and the end of 2014. But the dangers of the widely used Coumadin have drawn relatively little scrutiny, perhaps because the drug has clear benefits. Still, improper use has caused some patients incalculable suffering and, in some cases, greatly hastened deaths.