The study, by researchers at the University of Washington and Bastyr University in the US, was conducted on 524 children aged two to 11 and is one of the largest clinical trials on echinacea published to date.
In a finding that was not part of the trial's primary outcomes, children in the echinacea group experienced significantly fewer second and third upper respiratory tract infections (URIs) than children in the placebo group in the four-month trial.
But for primary outcomes - duration and severity of symptoms and adverse events recorded by parents - as well as secondary outcomes including peak severity of symptoms, number of days of peak severity and overall number of days of fever, the herb Echinacea purpurea, a type of echinacea used for medicinal purposes, produced no effect.
Upper respiratory tract infections (URIs) are a significant health burden in childhood, according to the authors. The average child has six to eight colds each year, each lasting seven to nine days, but there is little evidence that decongestants, antihistamines, and cough suppressants reduce symptoms in children younger than 12 years.
In total, parents reported 707 cases of URIs in the study, in 407 children. This included 337 cases treated with echinacea and 370 with placebo, showing a small benefit from the herb.
"It is conceivable that echinacea stimulated an immune response in study children that was too late to modify the URI for which it was given but provided a window of protection against another URI in the child," write the authors.
The echinacea or placebo was started at the onset of symptoms and continued for a maximum of ten days. Of the children with at least one URI, 64.4 per cent of those receiving placebo had more than one URI compared with 52.3 per cent of children receiving echinacea. The median duration of the URIs was nine days.
The authors note there was no difference in the rate of adverse events reported in the two treatment groups. However, rashes occurred during 7.1 per cent of the upper respiratory tract infections treated with echinacea and 2.7 per cent of those treated with placebo.
Mark Blumenthal, executive director of the American Botanical Council (ABC), said such an effect is not normally associated with the use of most echinacea products. He speculated that the rashes reported in this study might be due to allergic reactions to pollens in the echinacea preparation, since the product used contained the fresh-pressed juice of the above-ground part of the echinacea made in Germany.
Nevertheless, the authors concluded: "Given its lack of documented efficacy and an increased risk for the development of rash, our results do not support the use of echinacea for treatment of URIs in children two to 11 years old. Further studies using different echinacea formulations, doses, and dosing frequencies are needed to delineate any possible role for this herb in treating colds in young patients."
In a release from the ABC however, Dr Rick Kingston, associate professor of Experimental and Clinical Pharmaocology at the College of Pharmacy at the University of Minnesota, comments: "Although there was a statistically higher incidence of rash in the echinacea group compared to the placebo group, the overall occurrence was relatively low in both groups. This should not necessarily preclude the use of echinacea as the potential benefit of reducing subsequent URIs is significant."
Previous studies on echinacea preparations have found the herb to improve immune system function.
The study is published in JAMA (290(21):2824-30).