As I understand it, a combination of a few things.
One was a change to quality-of-care measurements. Lots of entities in the US health care system are evaluated on metrics around patient outcomes, and some of those look at management of physical pain. Changes to metrics for pain effectively pushed doctors toward a target of zero pain, and doctors began prescribing more medication to achieve that target.
Another is the allegation that pharmaceutical companies downplayed the risks of their newer formulations for pain medication, or even outright lied. Purdue, Endo, Allergan, Johnson & Johnson, Teva and others all are facing or have faced lawsuits over this. To take an example: Purdue marketed OxyContin as a breakthrough long-acting drug -- they claimed 12 hours of effectiveness -- which would reduce the risk of addiction. In reality, patients reported the effects wore off after as little as 4 hours, and Purdue's marketing and sales arms pushed doctors to prescribe more and higher doses. This naturally led to... addiction and overdoses.
Still another factor is that pharmaceutical companies seem to have been perfectly willing to overlook obvious abuse in order to move product and make money. It's not terribly hard to spot the patterns; there were cases of small (couple thousand people) towns where the local pharmacy would handle millions of doses of hydrocodone or oxycodone. And there have been lawsuits over that, too, with the drug companies mostly trying to reach settlements and avoid trials.
One was a change to quality-of-care measurements. Lots of entities in the US health care system are evaluated on metrics around patient outcomes, and some of those look at management of physical pain. Changes to metrics for pain effectively pushed doctors toward a target of zero pain, and doctors began prescribing more medication to achieve that target.
Another is the allegation that pharmaceutical companies downplayed the risks of their newer formulations for pain medication, or even outright lied. Purdue, Endo, Allergan, Johnson & Johnson, Teva and others all are facing or have faced lawsuits over this. To take an example: Purdue marketed OxyContin as a breakthrough long-acting drug -- they claimed 12 hours of effectiveness -- which would reduce the risk of addiction. In reality, patients reported the effects wore off after as little as 4 hours, and Purdue's marketing and sales arms pushed doctors to prescribe more and higher doses. This naturally led to... addiction and overdoses.
Still another factor is that pharmaceutical companies seem to have been perfectly willing to overlook obvious abuse in order to move product and make money. It's not terribly hard to spot the patterns; there were cases of small (couple thousand people) towns where the local pharmacy would handle millions of doses of hydrocodone or oxycodone. And there have been lawsuits over that, too, with the drug companies mostly trying to reach settlements and avoid trials.