Doctors in the US were paid to prescribe fentanyl to patients whether they needed it or not, it's been alleged.
NBC News reports an indictment has been filed against five doctors in Manhattan, who allegedly received $800,000 from a pharmaceutical company to prescribe the opioid painkiller.
Fentanyl is up to 100 times stronger than heroin, and has been linked to tens of thousands of deaths - including that of pop singer Prince and rocker Tom Petty.
Gordon Freedman, Jeffrey Goldstein, Todd Schlifstein, Dialecti Voudouris and Alexandru Burducea all pleaded not guilty.
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It's alleged the money was earmarked as "speaker's fees", but prosecuters say the fees were actually kickbacks from drugmaker Insys Theapeutics.
The events the doctors were speaking at were just social gatherings, they say.
"These prominent doctors swore a solemn oath to place their patients' care above all else," said Geoffrey Berman, US attorney for the Southern District of New York. "Instead, they engaged in a malignant scheme to prescribe fentanyl, a dangerous and potentially fatal narcotic 50 to 100 times more potent than morphine, in exchange for bribes in the form of speaker fees."
Insys founder and former chief executive John Kapoor is already facing charges over dodgy fentanyl prescriptions the New York Times reports.