For months, a simple generic drug has been saving lives on America’s battlefields by slowing the bleeding of even gravely wounded soldiers.

Even better, it is cheap. But its very inexpensiveness has slowed its entry into American emergency rooms, where it might save the lives of bleeding victims of car crashes, shootings and stabbings — up to 4,000 Americans a year, according to a recent study.

Because there is so little profit in it, the companies that make it do not champion it.

However, the drug is edging slowly closer to adoption as hospitals in New York and other major cities debate adding it to their pharmacies. The drug, tranexamic acid, has long been sold over the counter in Britain and Japan for heavy menstrual flow. After a groundbreaking 2010 trial on 20,000 hemorrhaging trauma patients in 40 countries showed that it saved lives, the British and American Armies adopted it. The World Health Organization added it to its essential drugs list last year, and British ambulances now carry it.

But outside Britain, it is used in very few civilian hospitals, though almost six million people around the world die each year of trauma — 400,000 of them in hospitals. A study published March 1 in BMC Emergency Medicine estimated that the drug could save up to 128,000 of those lives a year, 4,000 of them in the United States.