For most patients with diabetes and clogged arteries who have not had a heart attack, treatment with drugs and lifestyle changes are as effective at reducing death as immediate bypass surgery or angioplasty, researchers said Sunday.

For diabetics with a more severe form of heart disease requiring immediate surgery, bypass surgery is more effective than angioplasty at reducing heart attacks and strokes but not deaths, researchers reported at a meeting of the American Diabetes Association in New Orleans.

The findings are a second major blow to companies that manufacture the stents that are inserted into arteries after angioplasty to keep them open, a process that is now performed at least 1.24 million times each year in the United States.