Echinacea Fails To Block Cold Virus Infection

Researchers administered either echinacea or a placebo to 48 people for seven days before nasally inoculating them with a cold virus. The volunteers then continued to take echinacea or the placebo for another week. More than 90 percent of volunteers in both the echinacea and the placebo groups became infected with the cold virus, according to laboratory tests.

This result is consistent with other echinacea studies, said Steven Sperber, MD, lead author. "Although echinacea is widely used, a number of well-designed studies show it not to be effective in preventing the common cold," he said.

Echinacea purpurea, or purple coneflower, is one of the most popular herbal therapies in the United States for warding off colds. Echinacea capsules, juices, teas, and extracts line the aisles of health food stores. But if echinacea can not stop a cold virus from infecting a person, might the herb suppress the symptoms of a cold after a person is infected?

On this question, the results of the CID study were less clear cut. Not everyone in the CID study who was infected came down with a cold. In fact, actual cold symptoms developed in only 58 percent of those who received echinacea, compared with 82 percent of the placebo group. While this difference is suggestive, it can not be counted as statistically significant because of the small number of people in the study, Dr. Sperber explained.

Of the scientific studies that found evidence in favor of echinacea, most examined the herb's ability to treat cold symptoms rather than prevent colds from happening, Dr. Sperber noted. He speculated that the difference between the echinacea and placebo groups in his study might be the result a treatment benefit from echinacea, but this study was not designed to look specifically at treatment. "And many well-designed studies have found no treatment effect," he said.

Efforts to determine whether echinacea can foil the common cold suffer in part from the variety of echinacea products available, making it difficult to compare study results, Dr. Sperber added. "The medications may not be standardized from one brand to another. The particular components of the plant and the amounts of active ingredients may not be the same," he said. "Echinacea is not regulated by the Food and Drug Administration the same as an approved drug."

Nevertheless, interest in echinacea will probably continue to be strong, both for patients and physicians. "The cold is an illness that affects everybody, and for which there is no scientifically proven cure," Dr. Sperber said. "If echinacea were proven to be effective in well-conducted studies, I think it would likely be embraced. While many studies have already been conducted, there is a need for additional well-conducted studies in order to definitively answer the question about the role of echinacea in the management of colds."

Founded in 1979, Clinical Infectious Diseases publishes clinical articles twice monthly in a variety of areas of infectious disease, and is one of the most highly regarded journals in this specialty. It is published under the auspices of the Infectious Diseases Society of America (IDSA). Based in Alexandria, Va., IDSA is a professional society representing more than 7,500 physicians and scientists who specialize in infectious diseases. For more information, visit www.idsociety.org.