The herbal remedy turns out to be no more effective than a placebo, said the study, which is published in Thursday's "Journal of Medicine".
Echinacea, also known as purple coneflower, is recommended by the World Health Organization as a treatment for the common cold.
The study, led by Ronald Turner of the University of Virginia, tested echinacea on 399 volunteers to determine whether any of three preparations had an active ingredient that reduced the risk of infection or symptoms if an infection took hold, according to Reuters.
Although researchers tested the echinacea species originally used by Native Americans in the Midwest and endorsed by WHO, the treatment was as effective as a placebo.
There are many types of echinacea preparations, so it would be difficult to test them all, Turner says.
"Our study, however, adds to the accumulating evidence that suggests that the burden of proof should lie with those who advocate this treatment," he adds.
