Using heart stents to prop open diseased arteries has little advantage over medicines, exercise, and a better diet, according to researchers who said the devices should be a last resort for most patients.

Stents provided patients an “incremental” benefit in reduced pain and fatigue in a study published online Wednesday by the New England Journal of Medicine. After three years, the devices lost any advantage over a regimen of anti-cholesterol drugs, increased exercise, and a diet plan, the study found. An accompanying editorial said one-third of the 1 million stents implanted in America each year may be unnecessary.

The study poses an obstacle for stent makers led by Johnson & Johnson and Boston Scientific Corp. The devices may generate $5 billion in sales next year in a market still recovering from safety questions, analysts said. Its future depends on whether doctors and insurers embrace the logic of the new data, a Duke University cardiologist who co-wrote the editorial, Eric Peterson, said.

“There are a lot of forces, in terms of payment, the influence of manufacturers, and all the shiny, new devices that are coming on to the market, that are encouraging use,” Mr. Peterson said in a telephone interview. “There is enormous incentive in the medical industry to put things in patients.”

Physicians and insurers are starting to take notice, Mr. Peterson said. A subcommittee of the American College of Cardiology is rewriting its stent guidelines, and Medicare and Medicaid have commissioned a study of the procedure’s value.