A new study reveals that doctors who got a free meal from a pharmaceutical company were more likely to prescribe a medication that the drug company was promoting. The pricier the meals, the more prescribing rates for the drugs went up.

In the study published Monday in the journal JAMA Internal Medicine, researchers looked at government data on pharmaceutical company payments and how they may be correlated with U.S. doctors’ prescriptions choices for heart drugs and an antidepressant. They found that doctors who got even a single meal from a company promoting a certain drug were significantly more likely to prescribe the drug.

The more free meals, the more often the drugs were prescribed. The results showed that compared to doctors who did not take meals from pharmaceutical companies, doctors who got drug company-funded meals on four or more days were 1.8 times more likely to prescribe the statin rosuvastatin, 3.4 times more likely to prescribe the antidepressant desvenlafaxine, 4.5 times more likely to prescribe the blood pressure drug olmesartan and 5.4 times more likely to prescribed the blood pressure drug nebivolol.

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In the trial, 95% of the meals were less than $20, suggesting even small financial exchanges could influence behavior.

The study only found an association between the payments and prescribing behaviors and cannot definitively say whether the free meals definitely explain why a doctor prescribes a particular drug. Still, the study authors write that the findings “support the importance of ongoing transparency efforts in the United States and Europe,” and are supported by smaller, prior studies.

The researchers suggest more research be done to further explore the connection.

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