The federally funded study was what fans and foes of such substances say they have long needed rigorous, scientific testing. It found that patients who took an echinacea plant extract fared no better than those who took a dummy treatment.

"Our study . . . adds to the accumulating evidence that suggests that the burden of proof should lie with those who advocate this treatment," wrote Dr. Ronald Turner of the University of Virginia School of Medicine, who led the study, which appeared in Thursday's New England Journal of Medicine.

Echinacea, or purple coneflower, is sold over-the-counter in pills, drops and lozenges. With reported annual sales of more than $300 million, echinacea is one of the most popular medicinal herbs used by people to treat colds.

Dr. Wallace Sampson, an emeritus clinical professor of medicine at Stanford University School of Medicine, questioned why the government is wasting tax dollars on funding alternative medicine studies, some of which have turned out to be nothing but snake oil.

"Research into implausible remedies rarely produces useful information," wrote Sampson, who was not connected to the study.