The investigation was centered on doctors who were prescribing unnecessary opioids, as well as medical facilities that were “[preying] on addicts” to fork over cash for treatments that worsened their state, according to authorities.

NBC News reports:

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“Some doctors wrote out more prescriptions for controlled substances in one month than entire hospitals were writing,” Acting FBI Director Andrew McCabe told reporters. “To opioid addicts, these prescriptions escalate their dependence on drugs. They are a death sentence, plain and simple.”

The scams resulted in more than $1 billion in false billing uncovered in what Attorney General Jeff Sessions called “the largest health care fraud takedown operation in American history.” Much of that came out of the government’s pocket by illegally billing Medicare and Medicaid.

Among those charged were a fake Florida rehab facility that is alleged to have used gift cards and strip club visits to recruit addicts, and a Houston doctor who sold thousands of opioid prescriptions for cash.