American doctors prescribe - a lot
Unlike most European countries, the US does not have universal healthcare paid for by taxes.
Instead, Americans must get their own insurance - usually via an employer or the government.
"Most insurance, especially for poor people, won't pay for anything but a pill," says Professor Judith Feinberg from the West Virginia University School of Medicine.
"Say you have a patient that's 45 years old. They have lower back pain, you examine them, they have a muscle spasm.
"Really the best thing is physical therapy, but no one will pay for that. So doctors get very ready to pull out the prescription pad.
"Even if the insurance covers physical therapy, you probably need prior authorisation (from the insurer) - which is a lot of time and paperwork."
The CDC says opioid prescriptions have fallen by 18% from their peak in 2010. But the total is still three times higher than in 1999.
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In 2016, a study looked at the link between doctors, the free meals they received from drug companies, and the medication they prescribed.
The study found receiving free meals was "associated with an increased rate of prescribing the promoted brand-name medication".
Pharmaceutical companies say their reps are merely sharing information with doctors. But Professor Humphreys says there is a "corrupting" influence.
"We need a pharma industry, it's not that it's wrong," he says. "But you can't let the fox guard the hen house.
"I would create completely clear blue water between the people that manufacture drugs and all the training and operation of the healthcare system."
http://www.bbc.com/news/world-us-canada-41701718