Echinacea for preventing and treating the common cold

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Abstract
Background Echinacea plant preparations (family Compositae) are widely used in Europe and North America for common colds. Most consumers and physicians are not aware that products available under the term Echinacea differ appreciably in their composition, mainly due to the use of variable plant material, extraction methods and the addition of other components. Objectives To assess whether there is evidence that Echinacea preparations are 1) more effective than no treatment; 2) more effective than placebo; 3) similarly effective to other treatments in the prevention and treatment of the common cold. Search methods We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2007, Issue 3); PubMed (1997 to September 2007); EMBASE (1998 to April 2007); AMED (to August 2005) and the Centre for Complementary Medicine Research (1988 to September 2007). Selection criteria Randomized controlled trials (RCTs) comparing mono‐preparations of Echinacea with placebo, no treatment, or another treatment for prevention or treatment of common colds. Trials on combinations of Echinacea and other herbs were excluded. Data collection and analysis At least two review authors independently assessed eligibility and trial quality, and extracted data. Outcomes of interest in prevention trials were numbers of individuals with one or more colds, and the severity and duration of colds. In treatment trials outcomes were total symptom scores, nasal symptoms, and duration of colds. Main results Sixteen trials including a total of 22 comparisons of Echinacea preparations and a control group (19 placebo, 2 no treatment, 1 another herbal preparation) met the inclusion criteria. All trials except one were double‐blinded. The majority had reasonable to good methodological quality. Three comparisons investigated prevention; 19 comparisons investigated treatment of colds. A variety of different Echinacea preparations were used. None of the prevention trials showed an effect over placebo. Comparing an Echinacea preparation with placebo as treatment, a significant effect was reported in nine comparisons, a trend in one, and no difference in six. Evidence from more than one trial was available only for preparations based on the aerial parts of Echinacea purpurea (E. purpurea). Authors' conclusions Echinacea preparations tested in clinical trials differ greatly. There is some evidence that preparations based on the aerial parts of E. purpurea might be effective for the early treatment of colds in adults but the results are not fully consistent. Beneficial effects of other Echinacea preparations, and Echinacea used for preventative purposes might exist but have not been shown in independently replicated, rigorous RCTs.