Echinacea, which is derived from the purple coneflower, was used by Native Americans to ward off a wide variety of disorders and has been endorsed by the World Health Organization for treatment of the common cold.

The federally funded research was undertaken because more than 200 smaller studies had provided inconclusive and conflicting results about the benefits of the herb, which is derived from a common backyard plant, the purple coneflower.

Reporting in Wednesday's issue of the New England Journal of Medicine, researchers said volunteers who took an extract of Echinacea augustifolia and were exposed to a cold virus developed about the same number and severity of colds as those who did not take it.

"This is really a good, definitive study in terms of saying that echinacea doesn't work," said Dr. Viju T. John of Rush University Medical Center, who was not involved in the research.

Study Adds to Accumulating Evidence

Echinacea is widely touted as a treatment for viral and respiratory diseases and is the fourth best-selling herb in the United States, with sales estimated around $300 million a year, according to MarketResearch.com.

The plant was used by Native Americans to ward off a wide variety of disorders and has been endorsed by the World Health Organization for treatment of the common cold.

In the study published Wednesday, a total of 339 healthy volunteers were split into two groups. One was further divided into subgroups that received three different doses of the echinacea extract. The second group received an inactive placebo. Five days later, both groups were exposed to a rhinovirus through a nasal spray.

Most common colds are caused by rhinoviruses. The researchers used a strain identified as rhinovirus type 39, which is routinely used to study colds.

Among those receiving the herb, 81 to 92 percent caught colds, compared with 85 to 92 percent of those given the placebo.

"Our study ... adds to the accumulating evidence that suggests that the burden of proof (that echinacea works) should lie with those who advocate this treatment," wrote Dr. Ronald B. Turner of the University of Virginia School of Medicine, who headed the study.

No Effective Antiviral Cold Therapies

The results seem unlikely to convince those who swear by the herb. Managers at several Chicago health food stores noted that the study only tested one species of echinacea plant.

"They must have used the wrong kind," said Joyce deLuca, a manager at Southtown Health Foods. "It's a natural antibiotic and kills bacteria and viruses, as well as building the immune system."

At Bonne Sante Health Foods, which sells echinacea chews, pills, teas, drops and even enhanced water, manager Vivica Valcy said she chews the root of the plant to prevent colds.

When cold season starts, she said, people rush the store's supplement aisle.

"Oh wow. I couldn't really count how many," Valcy said. "That's one of our main sellers in the fall."

Kevin Park, manager at Life Spring Health Foods and Juice Bar, said the study would not discourage him from selling echinacea.

"Customers keep coming back and telling me good things," Park said. "I don't think it's a gimmick product. I think it's for real."

Microbiologist Dr. Kenneth Thompson, a University of Chicago researcher who studies antiviral compounds, said it is highly unlikely that echinacea of any kind could work.

Humans, he said, don't have the enzymes to utilize the active compound in the herb, so it does not reach blood vessels in the nasal cavity where cold viruses first infect a person.

Unfortunately, there are still no effective antiviral therapies that work on the common cold, Thompson said, which makes unproven remedies appealing to many cold sufferers.

'Advocates Often Dismiss Disproof'

John of Rush University Medical Center said that because the study failed to show any effect of echinacea on the immune system, it is unlikely that the compound would be of benefit in any kind of viral illness.

The National Center for Complementary and Alternative Medicine funded the study because of the growing popularity of the herbal remedy, Dr. Wallace Sampson wrote in a commentary that accompanied Turner's article.

Sampson, an emeritus professor of medicine at Stanford University and editor of the Scientific Review of Alternative Medicine, suggested it might be time for the federal government to stop wasting money on studies of unproven remedies that are not supported by scientific rationality.

Since 1999 the National Institutes of Health has spent almost $1.5 billion in grants for research into alternative methods, Sampson said. The alternative medicine center has spent almost half that amount and found no evidence that those methods work, he added.

Even when studies show complementary or alternative therapies don't work, such "disproof rarely leads the supplement industry to reduce production or the public to decrease use," Sampson said. "In fact, advocates often dismiss disproof."

"What is needed," he said, "is knowledge-based medicine, with randomized clinical trials of treatments with histories that indicate some reasonable chance of efficacy."