NEW YORK (Reuters Health) - People looking to shorten a bout with the common cold or reduce their symptoms by popping capsules of echinacea may not find relief, new study findings suggest.

Echinacea, derived from the purple coneflower, is an herb sold over the counter as an immune-system strengthener and cold remedy.

Despite a few studies that found the herb made a difference for cold sufferers, "there is no clear consensus about whether echinacea can benefit human health," lead author Dr. Bruce P. Barrett and colleagues write in the December 17th issue of the Annals of Internal Medicine.

To investigate, Barrett and a team of researchers at the University of Wisconsin in Madison compared the effects of echinacea in capsule form with a placebo pill in college students who believed they were coming down with a cold.

To participate in the study, the students had to report at least 2 of 15 listed cold symptoms. Participants were excluded if they reported having any of the symptoms for more than 36 hours or if they were taking antibiotics, antihistamines or decongestants.

The investigators did not detect a difference in cold duration between the echinacea and placebo groups, nor did they find any difference between the two groups in symptom severity, according to the report.

Colds lasted an average of 6 days for people in both groups, the report indicates.

Nonetheless, the authors note that echinacea is sold in a variety of forms and that just because the form of echinacea they tested had no health benefit doesn't necessarily mean that other forms will not help cold sufferers.

"Because (plant) chemical constituents vary among botanical species, growing conditions, plant part and extraction method, it is possible that one preparation would provide benefit while another would not," Barrett and colleagues write.

Barrett's team is calling for more research on echinacea's cold-fighting potential.

The echinacea capsules used in the current study contained a combination of whole unrefined plant material, including roots from Echinacea angustifolia and herb and root from Echinacea purpurea.

The students took four tablets six times for the first day and four tablets three times a day until cold symptoms resolved or for 10 days.

SOURCE: Annals of Internal Medicine 2002;137:939-946.

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