The new findings are based on a trial of 120 adults, who took 300 milligrams of an echinacea juice preparation daily at the first sign of a cold.
The results, reported in the Archives of Internal Medicine (164:1237-1241) this week, show that the herbal remedy had no effect on severity of symptoms and the time taken to recover from a cold compared to those given placebo.
The findings support the results of a study in children last year. This trial , published in the Journal of the American Medical Association, found that echinacea did not reduce the severity or duration of infections although it did appear to cut the number of respiratory tract infections in the children.
Echinacea is thought to stimulate the immune response and is widely sold as a cold remedy. However it is available in different forms, made from both the above-ground herb and/or root portions depending upon the species used. The product tested in both the new and JAMA study used the fresh-pressed juice of the above-ground part of the Echinacea plant.
The researchers from the US-based Marshfield Clinic concluded that "further studies using different preparations and dosages of E purpurea are necessary to validate previous claims."
It is not clearly understood which of echinacea's many chemical components are responsible for its effects.
