A U.S. federal agency says the number of deadly heroin overdoses in the country have more than quadrupled from 2010 to 2015. According to the National Center for Health Statistics, there were almost 13 thousand overdose deaths involving heroin in 2015, compared with a little over three thousand of such fatalities five years earlier. The center's research was based on death certificate data and did not examine underlying causes. A study by the Centers for Disease Control and Prevention found that the declining price of heroin and its increasing purity might be causing more people to use it. The latest stats come as America's struggle with opioid and heroin crises.