AMERICA’S health authorities are desperate for solutions to the country’s growing opioid scourge. Every day more than 90 Americans die from overdoses. About 2m have a drug addiction related to opioids prescribed by doctors for pain relief. Many turn to heroin and other illicit drugs as a result. It is now clear that stopping doctors from prescribing opioids too readily is essential if addictions and deaths are to be curbed.

A new study by Molly Schnell and Janet Currie from Princeton University crunched data on all opioid prescriptions written in America in 2006-14. They found a striking link: doctors trained in higher-ranked medical schools wrote far fewer opioid prescriptions than those trained in lower-ranked schools (or, surprisingly, osteopaths, whom you might expect to avoid using pharmaceuticals whenever possible).

This pattern held when the researchers compared doctors in the same speciality who practised in the same county—which suggests that the pattern is not caused by graduates from better schools seeing patients with medical problems that are less likely to require opioids. Nor does it appear to be simply a matter of graduates from more selective schools being generally more diligent: as these schools became more selective over time, their alumni did not grow more parsimonious with painkillers relative to peers from less prestigious institutions. This suggests that training plays a role.

The link with school rank was particularly striking for general practitioners, who write about half of all opioid prescriptions. The authors calculate that if all GPs had prescribed opioids at the same rate as those who graduated from Harvard, the top-ranked medical school (whose graduates are also the least enthusiastic prescribers), there would have been 56% fewer prescriptions and 9% fewer deaths resulting from overdoses.

There is no single solution to stopping America’s opioid epidemic. But training doctors to avoid unnecessary prescriptions is a good place to start.