It’s a new drug. And it’s a killer. Known on the street as “flakka,” the synthetic concoction is hitting hard in Florida, Tennessee, Kentucky, Ohio and other parts of the country. It’s causing a rash of emergency room visits and overdose deaths. In one highly publicized Florida case, a man reportedly high on flakka gnawed on and disfigured another man’s face before he was shot to death by police. Another user tried to break down the door of a police station in Fort Lauderdale, and a few weeks later, a man impaled himself while trying to climb a fence around...