A new study backs long-held suspicions that U.S. drug companies and doctors may have contributed to the nation’s ongoing opioid epidemic. The study found that people with family members who were prescribed opioid painkillers were more likely to report an overdose compared with those whose relatives were not prescribed opioids, Vox reports.

The study was published this week in JAMA Internal Medicine. 

For years, two theories for what has driven the nation’s worst addiction and overdose crisis have prevailed. One theory is that the overproduction and overprescription of painkillers have led to a major increase in addiction; the second is that “root causes,” such as mental illness, socioeconomic factors or a general sense of despair, are to blame.

Opioid experts generally agree that all of the above have played a role in the epidemic. However, this latest study sheds new light on the extent to which drug companies and doctors could have factored into the crisis.

For the study, researchers at Harvard University looked at health utilization data from 2004 to 2015 sourced from Optum Clinformatics Data Mart. In this data set, they found more than 2,300 people experienced an opioid overdose and compared their data with 9,200 individuals who didn’t. 

Ultimately, researchers found that people whose family members were prescribed an opioid were nearly three times more likely to have an overdose than those whose relatives were not prescribed such medication. Although the study shows only a correlation, it is very possible that at least in some instances, family members may borrow, buy or steal the drugs from a relative with a prescription.

“The claim that opioid overdose is just about ‘root causes’ rather than drug supply cannot be sustained in light of these findings,” tweeted Kim Humphreys, a drug policy expert at Stanford Unviersity who wasn’t involved in the study.

However, experts say simply removing opioids from the drug supply won’t solve the problem. For one thing, although prescription painkillers used to be the number one cause of overdoses in the U.S., fentanyl and heroin are now more likely to be the cause of an overdose. What’s more, if people addicted to prescription opioids are cut off from the prescription drugs, they could resort to these illegal alternatives, which are generally more dangerous.

Instead, addiction advocates recommend a multipronged approach to the problem, including increasing access to medication-assisted treatment, distributing more of the opioid overdose antidote naloxone and addressing those root causes of addiction.