CHICAGO  Two widely prescribed cholesterol-lowering drugs, Vytorin and Zetia, may not work and should be used only as a last resort, The New England Journal of Medicine said in an editorial published on Sunday.

The journal’s conclusion came as doctors at a major cardiology conference in Chicago saw for the first time the full results of a two-year clinical trial that showed that the drugs failed to slow, and might have even sped up, the growth of fatty plaques in the arteries. Growth of those plaques is closely correlated with heart attacks and strokes.

Merck and Schering-Plough, the companies that make Vytorin and Zetia, said on Sunday that despite the results of the trial, they would continue to promote their medicines as first-line treatments for high cholesterol.

The medicines are among the top-selling drugs in the world, with total sales of about $5 billion last year. About four million Americans take them.