A review of more than 700 previous studies concluded that echinacea does have a substantial effect in preventing colds and limiting their duration.

The analysis found that echinacea reduced the risk of catching a cold by 58 percent, and that the duration of a cold was significantly reduced.

The issue of whether echinacea is effective in the treatment of colds or not, has wavered back and forth, with some studies showing great effectiveness and others drawing the opposite conclusion. This review took a different approach to the issue and used statistical techniques to combine the results of existing studies, including only randomized and placebo-controlled trials.

But other experts are still skeptical about the technique used to reach their conclusions, holding fast to their own, less optimistic, findings.

Dr. Coleman, senior author of the paper, points out that there are several reasons why even a carefully devised study might fail to show an effect that actually does exist. Since there are more than 200 species of cold viruses, a study might be using a species against which echinacea happens to be ineffective. But that doesn‘t mean it won‘t work for other strains. Additionally, some studies may not use large enough doses of the herb, and others may be using less potent types of echinacea.

New York Times July 24, 2007

The Lancet Infectious Diseases; 7(7):473-80 July, 2007