The line at Dr. Abdelrahman Mohamed's pain clinic snaked down the hall, out the door and sometimes into the parking lot, full of patients with cash in fists.

Federal agents knew Mohamed, the owner of Hamblen Neuroscience Center in Morristown, as the "drive-through doctor" who signed an average of 60 prewritten prescriptions for pain pills per day. Sales reps for Endo Pharmaceuticals knew him as a Grade A customer and saw nothing wrong.

When suspicious local pharmacists stopped filling the prescriptions, Mohamed's Endo rep stepped in to help.

"This is my top writer," the rep wrote in an email. "He is having a hard time getting Opana for his current patients and now switching them over to other medications."

Red flags ignored

Mohamed wrote thousands of prescriptions before he headed to federal prison last year for health care fraud. Endo reps pushing Opana ER, their flagship painkiller, dropped in routinely on sales calls at his and other pill mills across Tennessee for a decade from 2007 to 2017 and looked the other way amid glaring signs of fraud and drug-dealing, Tennessee Attorney General Herbert Slatery says in a lawsuit against the company.

"Endo's sales representatives and district managers observed and ignored red flags for abuse or diversion of opioids," Brant Harrell, an assistant state attorney general, wrote.

The lawsuit, initially filed under seal in Knox County Circuit Court, became public last week after the Knoxville News Sentinel filed a motion arguing taxpayers deserve to know who's at fault for the opioid epidemic that's swept the state. A similar lawsuit filed last year targeted Purdue Pharma, maker of OxyContin.

Extended-release painkillers like Opana ER, introduced in 2006, and rival OxyContin, introduced a decade before, were meant to offer relief from chronic pain for the elderly, the aching, the injured and the dying. But addicts soon figured out how to crush the pills, then snort or inject them for an instant high.

Children in Tennessee are born dependent on drugs, most commonly opioids, at a rate 10 times the national average. The state reported 1,268 overdose deaths in 2017 alone — 69% higher than the national rate.

The loyalist club

Endo executives pinned the sales strategy for Opana ER on aggressive approaches to doctors and a tracking system that awarded letter grades to top prescribers, according to Slatery's complaint. By 2011, the East Tennessee sales district reported more Opana ER prescriptions than any other in the U.S. Nationwide Opana sales reached $384.3 million that year.

Mohamed, who prescribed an estimated 604,379 Opana ER pills from 2007 to 2014 alone, held an A grade, as did 168 other Tennessee physicians. Endo later declared him an Opana "loyalist."

An Endo sales rep visited Mohamed's office at least 45 times in a single year, according to the lawsuit — an average of every eight days. That rep would have seen patients passing out in the waiting room, employees filling out prescription pads in advance, a parking lot full of out-of-county and out-of-state license plates, and a doctor whose appointments lasted two minutes at most, according to the lawsuit.

More:Opioid crisis: Some providers named in state's Opana suit disciplined, others still practicing

When local pharmacists started refusing Mohamed's prescriptions, Endo "sprang into action" and "actively worked to find pharmacies willing to fill the obscene volume of Dr. Mohamed's Opana prescriptions," Harrell wrote.

Sales reps in Middle Tennessee similarly ignored red flags in visits to Dr. Samson Orusa's office in Clarksville, Harrell wrote. Orusa's clinic was housed in a run-down trailer with signs pasted to the door that welcomed walk-ins, offered a 24-hour phone number for prescription renewal and encouraged cash payment.

Orusa, who saw an average of 60 or more patients per day, faces a federal indictment on charges of illegal distribution of prescription drugs, health care fraud and money laundering.

Story of the stats

Endo executives tracked their sales figures in real time down to the pill and knew their drug — touted as "abuse-resistant" — had soared in popularity among addicts, according to the lawsuit. The company sold nearly a million more Opana ER pills in Knoxville from 2007 to 2014 than in New York City, Los Angeles and Chicago combined.

Corporate culture encouraged sales reps to avoid asking questions. A district sales manager spoke up in 2007 with concerns about Dr. Frank McNiel of Bearden Healthcare Associates in Knoxville. McNiel, one of the top pain pill prescribers in the U.S., accounted for one out of five opioid products prescribed in the Knoxville area, according to court records.

"He has a full staff and his office is always packed," the manager wrote. "I spoke to the local pharmacist and he stated that a lot of Dr. McNiel's patients pay cash. ... Dr. McNiel prescribes almost three times what the average (primary-care physician) writes and I am not sure how legitimate his practice appears to be. As an example, Dr. McNiel has written 3,800 scripts of OxyContin (Opana's top rival) through September of this year, which seems almost impossible even for a pain clinic."

Endo's top ethics and compliance officer, not identified by name in the lawsuit, brushed off the warning.

"Thanks for your note," the executive replied. "We actually looked into Dr. McNiel earlier this year and didn't find any evidence of suspected diversion."

McNiel surrendered his medical license last year after a series of sanctions by the state Board of Medical Examiners. He denied any wrongdoing.

Endo pulled Opana from the market in 2018 under pressure from the U.S. Food and Drug Administration. The lawsuit, which seeks unspecified damages, argues Opana caused more harm in Tennessee than any other state.

The company's lawyers have yet to file a response.