Illegal drugs like heroin and illicit fentanyl cause thousands of deaths each year in the United States, but legally prescribed opioids were responsible for over 40 percent of the more than 40,000 opioid overdose deaths in 2016. Given concerns about the pharmaceutical industry’s role at the beginning of the opioid crisis, it’s only natural that public health researchers would ask what role pharmaceutical companies play in the current state of affairs. New research published Monday in the Journal of the American Medical Association detailing their findings suggest that some members of the industry are making things much worse.

In the research letter, first-authored by Dr. Scott E. Hadland of the Grayken Center for Addiction in Boston, the team show evidence that doctors who are paid for “non-research” activities by pharmaceutical companies prescribe more opioids. It’s no surprise that companies do this: Doctors are known to be paid for being brand ambassadors or “thought leaders,” occasionally receiving honorary fees in addition to meals, travel budgets, consulting fees, or education for speaking at conferences. Doctors that receive payments from drug companies often argue that they only prescribe the drugs patients need and strictly represent companies whose science gives patients the best care. But the trends presented in the paper suggest a much murkier situation.

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INSYS Therapeutics, which makes the sublingual fentanyl spray Subsys, has paid doctors over $4.5 million in speaker fees and other perks.

The researchers point to evidence they gathered by comparing a list of physicians who prescribed opioids under Medicare Part D with numbers from the US Open Payments databases, which tracks money that drug and medical device companies pay to doctors and hospitals. By examining the prescribing and payments records for 369,139 doctors, they found that a small number of doctors who prescribe opioids in 2015 had received payments from drug companies in 2014 and that the more those doctors were paid, the more opioids they prescribed.

“Of physicians who prescribed opioids under Medicare Part D, seven percent received non-research payments related to opioid products in 2014,” they write. “These payments were associated with greater opioid prescribing in 2015.” The payments issued by one company, INSYS Therapeutics, was shown to have accounted for more than 50 percent of all the money paid to doctors by pharmaceutical companies during the study period. There’s an obvious conflict of interest when doctors’ influence is up for sale, and in the case of INSYS, the US government has intervened.

According to federal prosecutors, these payments were more than just the usual marketing gigs. They were kickbacks in a racketeering scheme that led to the arrest of the company’s founder and prison time for a doctor. On May 2, The New York Times Magazine covered the scandal, showing that INSYS sales reps specifically targeted doctors that needed cash.

As drug companies’ roles in fueling the opioid epidemic become clearer, state, local, and federal authorities have begun holding them responsible for deceptive marketing. Alabama, for instance, is suing Purdue, the company that makes Oxycontin. This study, showing evidence that many long-held suspicions about the industry are true, is likely just one of many such papers to show how the deep pockets of drug companies can influence public health crises.