Marketed and studied medicinal products contain different species (E. purpurea, E. angustifolia, E. pallida), different organs (roots and herbs) and different preparations (extracts and expressed juice). Their chemical compositions are very different.[5][6]
Multiple scientific reviews and meta-analyses have evaluated the published peer reviewed literature on the immunological effects of Echinacea. Reviews of the medicinal effects of Echinacea are often complicated by the inclusion of these different products.[7] Evaluation of the literature within the field suffers generally from a lack of well-controlled trials, with many studies of low quality.[7][8][9][10]
A 2007 study by the University of Connecticut combined findings from 14 previously reported trials examining Echinacea and concluded that Echinacea can cut the chances of catching a cold by more than half, and shorten the duration of a cold by an average of 1.4 days.[8][11] However, Dr. Wallace Sampson, an editor of Scientific Review of Alternative Medicine and a Stanford University emeritus clinical professor of medicine, says that the referenced trials lack the similarities necessary to provide definitive results when combined into one report. "If you have studies that measure different things, there is no way to correct for that. These researchers tried, but you just can’t do it."[12]
A 2003 controlled double-blind study from the University of Virginia School of Medicine and documented in the New England Journal of Medicine[13] stated that echinacea extracts had "no clinically significant effects" on rates of infection or duration or intensity of symptoms. The effects held when the herb was taken immediately following infectious viral exposure and when taken as a prophylaxis starting a week prior to exposure. In a press release, Dr. Michael Murray, the Director of Education for Factors Group of Nutritional Companies, a manufacturer of Echinacea-related products, calls the study "faulty and inaccurate."[14] According to Dr. Murray, none of the three extracts used on the 399 study participants contained all three of the components of Echinacea responsible for its immune-enhancing effects: polysaccharides, alkylamides and cichoric acid. In addition, Dr. Murray said "the standard dosage for dried Echinacea angustifolia root is normally three grams per day or more and this study used less than one gram."
An earlier University of Maryland review based on 13 European studies concluded that echinacea, when taken at first sign of a cold, reduced cold symptoms or shortened their duration.[15] The review also found that three of four published studies concluded that taking echinacea to prevent a cold was ineffective.
The European Medicines Agency (EMEA) assessed[16] the body of evidence and approved the use of expressed juice and dried expressed juice from fresh flowering aerial parts of Echinacea purpurea for the short-term prevention and treatment of the common cold. According to their recommendations:
It should not be used for more than 10 days. The use in children below 1 year of age is contraindicated, because of theoretically possible undesirable effect on immature immune system. The use in children between 1 and 12 years of age is not recommended, because efficacy has not been sufficiently documented although specific risks are not documented. In the absence of sufficient data, the use in pregnancy and lactation is not recommended.[17]