Doctors from the lowest-ranked U.S. medical schools are three times as likely to prescribe opioids as those trained at Harvard, the top-ranked U.S. school, according to a new research paper.

Why it matters: The authors argue that doctor training is an overlooked driver of the American opiate epidemic.

Expand chart Data: National Bureau of Economic Research; Chart: Andrew Witherspoon / Axios

In a paper published Monday with the National Bureau of Economic Research, Princeton economists Molly Schnell and Janet Currie find a "striking relationship" between the frequency of prescriptions and medical school attended: doctors trained at top-ranked medical schools like Harvard, Johns Hopkins, Penn, Stanford and Washington University in St. Louis "are less likely to write any opioid prescriptions," they write. And such doctors who do prescribe opiates do so at a lower rate than the typical MD.

How the study was done: The paper is based on a cross-referencing of prescription data from 2006 to 2014 and medical school rankings by U.S. News and World Report.

The authors considered the possibility that their study reflected a propensity of elite medical students to develop a conservative approach to prescribing opiates, rather than their education at these institutions. They also considered the possibility that doctors from less elite schools are systematically more likely to see more patients in need of opiates.

But the authors batted away the first point by showing that the difference in prescription rates between elite and lower-ranked schools has shrunk over time, even as the top schools have become more selective. They argue this shows a diffusion of good educational methods from top institutions to the rest.

If the difference in prescription rates were about the type of students at elite institutions, they said, the difference would have grown over time.

The study also finds the difference in prescription rates is maintained when you control for the doctor's speciality and place of practice.

The GP Problem: Another important finding was general practitioners accounted for 48% of opioid prescriptions, even though they were just 27% of the doctors studied.

General practitioners were less likely to be from elite schools, but when they were trained at Harvard, they averaged 180 opioid prescriptions a year; when they were from the lowest-ranked schools, they handed out an average of 550 opioid prescriptions a year.

"If all GPs prescribed like those from [Harvard], we would have had 56.5% fewer opioid prescriptions and 8.5% fewer deaths over the period 2006 to 2014," they wrote, making outreach to this type of doctor critical.

What should policymakers do: This paper argues that training matters, but it doesn't investigate what elite institutions are specifically doing to produce more restrained prescribers. That said, the authors point to data showing that the effect of a pedigree is lessened when the doctor — regardless of medical school — is in a practice requiring specialized pain management training. They argue this could be reason to require all MDs to take classes as well, and the Trump Administration's Chris Christie- led opiate commission recommended that such training be mandated.