Taking echinacea had no significant effect on the duration or severity of the common cold, according to the results of a randomized, blinded trial.
The average duration of symptoms was 6.34 days in patients taking echinacea in a blinded fashion and 6.76 days in patients who knew they were receiving the herb, according to Dr. Bruce Barrett of the University of Wisconsin in Madison and colleagues.
There also was no significant difference in cold severity as assessed by the Wisconsin Upper Respiratory Symptom Survey, the researchers reported Dec. 21 in Annals of Internal Medicine.
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"However, the trends were in the direction of benefit, amounting to an average half-day reduction in the duration of a week-long cold, or an approximate 10 percent reduction in overall severity," they noted.
Indigenous peoples of North America used echinacea for numerous illnesses, and it has been used therapeutically for nearly a century in Germany where plant-based medicine has long been widely practiced. Extracts of the plant are thought to boost immunity.
Many studies to date have attempted to clarify echinacea's cold-fighting effects, and although some early trials showed positive results, most were manufacturer-sponsored and their quality was questionable, according to Barrett and colleagues.
More recent trials have yielded conflicting results, and meta-analyses, which review data from multiple studies, have failed to provide clear results or interpretations.
To address whether echinacea extracts could significantly influence the outcome of upper respiratory tract infections, Barrett and colleagues enrolled 719 patients in a trial conducted under the auspices of the National Institutes of Health's National Center for Complementary and Alternative Medicine.
Patients were randomized to four groups: echinacea (10.2 g of dried echinacea root during the first day and 5.1 g per day for four additional day) taken either knowingly or not knowing whether it was echinacea or placebo, placebo, or no treatment at all.
Participants who received placebo had a mean duration of 6.87 symptomatic days, while those who received no treatment had a mean duration of 7.03 days.
Severity scores were 264 in the placebo group and 286 in the no-treatment group.
Despite the fact that trends were seen for some improvement with echinacea, the investigators argued that only about one in four people would consider the degree of benefit they found to be worth the cost and trouble.
Barrett and colleagues concluded that echinacea is likely to have only "a small beneficial effect" for treating colds, basing this conclusion on their data as well as "a reasonably substantial body of scientific evidence."
While they found no statistically significant evidence for effect of echinacea, the authors said clinically meaningful benefits in some can't be ruled out.
"Individual choices about whether to use echinacea to treat the common cold should be guided by personal health values and preferences, as well as by the limited evidence available," they reported.