I was reading up on this the other day, quoting from a previous Insys employee on the subject of their fentanyl product 'subsys':
“It's only FDA approved for cancer patients with breakthrough cancer pain. If you don't have cancer, and breakthrough cancer pain, no insurance company is going to pay for this medication,” whistleblower Patty Nixon told us.

But most -- 90 percent -- of the patients referred to Nixon and her colleagues for Subsys sales were cancer-free, she said. “When 10 percent of the patients’ charts that came over or less were cancer patients, that's not a lot of money. Nobody's going to get rich off of that,” she said.

“But you have this whole other world of everybody. That ‘my back hurts’ money, ‘my knee hurts’ money,” said Nixon. The solution, she said, was for company reps to tell insurance companies that patients had cancer when they did not."

Source:
http://interactive.fusion.net/death-by-fentanyl/intro.html