More than 60 percent of people killed by opioid overdoses were driven to the addictive pills by a chronic pain condition, according to a major report.
The number of opioid-related deaths quadrupled between 1999 and 2015, from around 8,000 to more than 33,000.
The Columbia University study - the largest ever on opioid deaths - analyzed the prescriptions of 13,000 victims through Medicaid to find almost two-thirds of them had been diagnosed with chronic pain, and a significant proportion of them also suffered depression and anxiety.
Around a third of victims had been diagnosed with their pain condition within 12 months of their death.
Mark Olfson, MD, professor of psychiatry at the university's medical center and lead investigator of the study, said the data provide a clear picture of the American healthcare system: big on pills, vague on alternative methods.
'The frequent occurrence of treated chronic pain and mental health conditions among overdose decedents underscores the importance of offering substance use treatment services in clinics that treat patients with chronic pain and mental health problems,' he said.