It used to be common for drugmakers to ply medical students with meals and gifts as a way to curry favor with America's next generation of doctors.

But times are changing.

To curb the influence of drug companies, most U.S. medical schools have now instituted policies that restrict or ban gifts altogether. The policies appear to have a lasting effect.

A study just published in BMJ, the British Medical Journal, finds that policies restricting gifts may reduce how often doctors who were med students when the policies were in force prescribed newly marketed drugs.

The researchers found that physicians who attended U.S. medical schools with policies restricting gifts were less likely to prescribe two brand-name drugs – Vyvanse, for ADHD, and Invega, an antipsychotic — than older, cheaper and similarly effective alternatives. There was no apparent difference in prescriptions for Pristiq, an antidepressant.

These results suggest, though they don't prove, that policies restricting gifts to med students can affect what they prescribe when they become doctors.

That's a good thing, according to Dr. Joseph Ross, associate professor of medicine at Yale University and co-author of the study.

Ross says that gift-giving creates a relationship between physicians and pharmaceutical manufacturers that leads to unnecessary prescribing of newer, pricier — but not necessarily more effective --drugs. "[The pharmaceutical] industry, whose real interest is in promotion and marketing their products, should have no role in the education of physicians ... There's just no reason for it," he says.

Ross has company. In 2007, the American Medical Student Association released its first annual PharmFree scorecard, which evaluates U.S. medical schools on how they regulate medical students' exposure to the pharmaceutical industry. These scorecards have created competition among schools to do better, resulting in more schools adopting policies restricting gifts.

Some new drugs have significant advantages over older ones. These innovative drugs probably wouldn't be hurt by a cutback in physician-targeted marketing, Ross says. "When a new drug comes to the market and it really makes a difference, people are going to be eager to use it," he says.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.