United States prosecutors on Thursday charged over 400 people in connection with a healthcare fraud worth $1.3 billion, AFP reported. The Justice Department said 120 of the 412 defendants had been charged with opioid-related scams. Opioids are a class of drugs used to relieve pain.

Attorney General Jeff Sessions (pictured above) called the action the “largest healthcare fraud takedown operation in American history”. “While today is a historic day, the department’s work is certainly not finished. In fact, it is just beginning,” Sessions said.

He said some doctors, nurses and pharmacists had chosen to violate their oaths and put greed ahead of their patients. “They seem oblivious to the disastrous consequences of their greed,” Session said, according to the Chicago Tribune. “Their actions not only enrich themselves, often at the expense of taxpayers, but also feed addictions and cause addictions to start.”

Six Michigan doctors used to prescribe opioids without any reason, according to the prosecutors. Sessions said a clinic in Houston allegedly sold prescriptions for opioids in exchange for cash.