Since 2000, deaths from opioid overdoses in the United States have gone up by 200 percent. While heroin is a significant part of that, according to the Centers for Disease Control and Prevention, “natural and semisynthetic opioids, which include the most commonly prescribed opioid pain relievers … continue to be involved in more overdose deaths than any other opioid type.”

These addictive pain relievers are increasingly accessible. Sales of prescription opioids have gone up by 300 percent since 1999, and according to a new study in Annals of Internal Medicine, even people who’ve previously overdosed often have an easy time obtaining the drugs.

The study looked at 3,000 patients who overdosed on prescription opioids, but didn’t die. Researchers at Boston Medical Center and Harvard University followed each one for two years, or until they overdosed again, left their insurance, or turned 65, whichever came first. (Some of the patients who enrolled towards the end of the study were followed for a shorter amount of time.)

During this period, 91 percent of the patients got opioid-painkiller prescriptions at least one more time after their overdoses. And 7 percent of them overdosed again, with overdoses becoming likelier the higher the dosage they’d been prescribed. But it wasn’t that patients were jumping from doctor to doctor to keep getting the drugs—70 percent of people who got new prescriptions got them from doctors who’d treated them before the overdose.

The researchers don’t know why these doctors continued to give opioids to such at-risk patients, but speculate that they just didn’t know about the overdose. In an editorial accompanying the study, Jessica Gregg, a physician at the Portland social-services agency Central City Concern, cites the difficulties of pain management as one possible reason. It’s hard to tread the line between treatment and addiction enablement—only patients truly know how much pain they’re in.

Flawed health systems may also play a role. “As noted by the authors, there are currently no widespread systems in place, either within health plans or through governmental organizations, for notifying providers when overdoses occur,” Gregg writes. “Until such systems exist, providers will be left to act with dangerously limited knowledge.”