Previous studies have found a link between the condition and pain pills.

That's one reason why labels on over-the-counter pain pills advise users to see their doctor within a few days.

Critics say that doctors were urged to prescribe pain pills during the 1990s to patients who may not have needed them.

Doctors who prescribed the most pain pills were taken on all-expenses-paid retreats.

Additional transcripts revealed that he had prescribed pain pills to at least one patient with whom he'd had an affaira clear conflict of interest.