A major scientific review of studies on Echinacea concludes that it does help prevent and limit the duration of colds:

"In the latest twist, a review of more than 700 studies has concluded that echinacea has a substantial effect...The paper, published in the July issue of The Lancet Infectious Diseases, used statistical techniques to combine the results of existing studies and reach conclusions based on the larger sample that resulted. The researchers selected only those trials that used randomized and placebo-controlled techniques: 14 studies involving 1,356 participants for the number of colds and 1,630 for the prevention of colds. The studies varied in the dosages of the herb, the duration it was taken and the species of echinacea used, and the number of participants ranged from 40 to more than 300.

The analysis concluded that echinacea reduced the risk of catching a cold by 58 percent. It also found that the herb significantly shortened the duration of a cold, but there was no general agreement about the magnitude of this effect.

"Our analysis doesnt say that the stuff works without question," said Dr. Craig I. Coleman, an assistant professor of pharmacy practice at the University of Connecticut, and the senior author of the paper. "But the preponderance of evidence suggests that it does."...Dr. Bruce P. Barrett, an associate professor of family medicine at the University of Wisconsin who was not involved with the review, said he was not convinced of the value of combining the studies in a single analysis.

"If youÂre testing the same intervention on the same population using the same outcome measures, then meta-analysis is a very good technique," Dr. Barrett said. "But here every one of those things fails." One of Dr. BarrettÂs papers on echinacea was included in the analysis.

Other experts also expressed skepticism...(a 2005 study in the New England Journal of Medicine found no benefit, leading the head of the NIH's complementary medicine division to conclude that echinacea was worthless as a cold preventative/remedy)...Dr. Barrett said there was probably little harm in using echinacea, and he was cautiously optimistic that the herb does have a very small positive effect.

"ThereÂs some danger of kids getting a rash, and it would be inadvisable to give it to women in the early stages of pregnancy," he said. "But if adults believe in echinacea, theyÂre going to get benefits  maybe from placebo  but theyÂll get benefits."

Dr. Coleman, who described himself as "not much of a pill taker," hedged a bit when asked if he planned to use echinacea himself. "IÂll probably consider taking it if I feel a cold coming on," he said. "These results have pushed me toward the idea. Whether IÂm actually going to take it, well, weÂll see."

http://www.nytimes.com/2007/07/24/health/24echi.html?ex=1187323200&en=2ca8c5f5055ce1dc&ei=5070

http://www.nytimes.com/2005/07/28/health/28cold.html?ex=1187323200&en=f5c123a36afe93a7&ei=5070

Maybe it's just a placebo effect, but I think I may have had some luck in preventing colds via echinacea (difficult as it is to be sure you were actually exposed), though one odd effect at times seems to be that I wind up getting the cold, only much delayed.

It would now be nice to have solid evidence on just which of the many Echinacea preparations on the market have good active ingredients...