I've read a few coherent accounts of what happened here in the US, and several of them blame changing Medicare/Medicaid quality-of-care guidelines. Specifically

I've read a few coherent accounts of what happened here in the US, and several of them blame changing Medicare/Medicaid quality-of-care guidelines. Specifically, that at one point one of the guidelines -- which factor into how much various entities in the system get paid -- changed from measuring whether pain was appropriately managed, to measuring whether pain was being eliminated. Which in turn led to an explosion of prescriptions of high-strength pain medications in order to hit the measure. Having some experience with Medicare's version of the guidelines, most of them are sensible and do directly relate to whether someone's being treated in a way that will lead them to be healthy and happy in the long term. But it appears that one was a major mistake.