All pharmaceutical marketers had to do was show up at a doctor’s office and promise a meal or cash for a speaking engagement. The more they did that, the more opioid painkillers the doctors prescribed — and the more people died of drug overdoses, according to a new study.

By cross-referencing a cache of county-level, publicly available interactions between drug marketers and physicians with mortality and prescription data, researchers at Boston Medical Center’s Grayken Center for Addiction and New York University School of Medicine discovered that more marketing visits were associated with an increase in overdose mortality one year later. The researchers examined 434,754 payments from Aug. 1, 2014, to Dec. 31, 2015.

“Our findings suggest that direct-to-physician opioid marketing may counter current national efforts to reduce the number of opioids prescribed and that policymakers might consider limits on these activities as part of a robust, evidence-based response to the opioid overdose epidemic in the United States,” researchers wrote in the first-of-its-kind analysis, published Friday in the journal JAMA Network Open.

Researchers in the study cautioned that drugmakers may have marketed more in areas with already-high opioid prescription rates, which could partially explain the increased mortality rates in those areas. Still, it’s “potentially concerning that physicians in such counties would receive further marketing for opioids,” according to the researchers.

The drug reps didn’t bombard these physicians with high-level marketing or glossy advertisements. The doctors referenced in the study instead experienced what's referred to as “direct-to-physician” marketing, like sales representatives showing up at their local practice with free samples, lunch for the office, or pledges to pay speaker fees and cover travel costs to an event.

Drugmakers spent $39.7 million marketing drugs to nearly 68,000 physicians across the U.S. between August 2013 and December 2015, according to the study. But the amount they spent on marketing didn’t necessarily make a difference on prescription rates; what mattered more was that drug reps continued to show up and multiple interactions with doctors.

“In the midst of the opioid epidemic, it is critical to address what may be contributing to people misusing and overdosing on prescription opioids, and our study indicates that, across the country, marketing to doctors may strongly influence these outcomes,” Scott Hadland, a physician and lead author of the study, said in a news release.

In another study, published in May 2018, researchers at Boston Medical Center found that in 2014, the doctors who received some level of opioid drug marketing, like meals or consulting fees, increased their opioid prescriptions by 9 percent the next year, compared to doctors who didn’t receive the same marketing. In that study, the drugmakers that doled out the most cash to physicians were INSYS Therapeutics, the maker of a fentanyl painkiller called Subsys; Teva Pharmaceuticals; and Janssen Pharmaceuticals. In August, INSYS reached a $150 million settlement deal with the U.S. Department of Justice to resolve an investigation into allegations that its marketers paid doctors kickbacks to prescribe Subsys.

Prescriptions for opioid painkillers have steadily declined in tandem with a growing awareness of their impact on a nationwide epidemic of drug overdose deaths. Even so, drug overdose deaths remain at a record high as former prescription drug users move on to more potent — and illegal — opioids, like heroin and fentanyl. For that reason, opioid makers and distributors are tied up in a bevy of civil lawsuits across the country that blame them for a crisis that killed more than 70,000 Americans in 2017.