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Previous studies of Echinacea have reported success varying from 10% to 50% in the treatment of colds. A few randomised trials have reported only a small effect in preventing colds.
In this randomised, double blind, placebo controlled study the authors report on the effect of 10 days of treatment with dried, encapsulated, whole plant Echinacea starting within 36 hours of onset of symptoms in 142 students reporting common colds (69 Echinacea, 73 placebo). Their primary objective was to measure the severity and duration of reported upper respiratory tract infections. They concluded that there was no statistical difference between the two groups. They do, however, believe this should not be the last word on the use of Echinacea in the treatment of colds because (1) they used whole plant mixture rather than extracts as reported in previous trials, (2) they studied a healthy population of students in whom the clinical effect would be small, and (3) the trial was of modest size and would have missed an effect of 5–10%. Furthermore, they did not confirm infection by serological testing or inflammatory markers and simply based it on reported symptoms. This raises doubt about the exact aetiology of the illness.
This is a well designed study which clearly shows that whole plant Echinacea has no significant clinical effect on the course and severity of the common cold, although it is unlikely that this will end discussion on this subject.