The U.S. government will pay for a large study measuring whether safe injection sites can make a dent in the nation’s overdose epidemic. The grant, announced Monday, will study three sites where people can use heroin and other drugs and be revived if they take too much. The award is expected to provide more than $5 million over four years to New York University and Brown University. Researchers will study two sites operating in New York City and one opening next year in Providence, Rhode Island. Such sites are not universally accepted. Opponents are worried that they encourage drug use.