A recent study of opioid-related deaths in Massachusetts underlines this crucial point, finding that prescription analgesics were detected without heroin or fentanyl in less than 17 percent of the cases. Furthermore, decedents had prescriptions for the opioids that showed up in toxicology tests just 1.3 percent of the time.

Alexander Walley, an associate professor of medicine at Boston University, and five other researchers looked at nearly 3,000 opioid-related deaths with complete toxicology reports from 2013 through 2015. “In Massachusetts, prescribed opioids do not appear to be the major proximal cause of opioid-related overdose deaths,” Walley et al. write in the journal Public Health Reports. “Prescription opioids were detected in postmortem toxicology reports of fewer than half of the decedents; when opioids were prescribed at the time of death, they were commonly not detected in postmortem toxicology reports….The major proximal contributors to opioid-related overdose deaths in Massachusetts during the study period were illicitly made fentanyl and heroin.”

The study confirms that the link between opioid prescriptions and opioid-related deaths is far less straightforward than it is usually portrayed. “Commonly the medication that people are prescribed is not the one that’s present when they die,” Walley told Pain News Network. “And vice versa: The people who died with a prescription opioid like oxycodone in their toxicology screen often don’t have a prescription for it.”