Objectives: To review the evidence regarding the effectiveness of orally ingested Echinacea extracts in reducing the incidence, severity, or duration of acute upper respiratory infections (URIs).
Search strategies: Information from a wide range of sources was used as background material. More than 100 articles, books, and book chapters were reviewed for content and further references. Database searches, bibliographic reviews, and conversations with experts were carried out iteratively from January 1997 to February 1999.
Selection criteria: Published or unpublished reports of all blinded placebo-controlled randomized trials of any Echinacea formulation used as a treatment or for the prevention of URIs.
Data collection and analysis: Review considerations included randomization, blinding, power, validity and clinical relevance of outcome measurements, inclusion and exclusion criteria, indistinguishability of treatment and placebo, and appropriateness of conclusions for the data presented. MAIN RESULTS. Nine treatment trials and 4 prevention trials fitting the selection criteria were found. Eight of the treatment trials reported generally positive results, and 3 of the prevention trials reported marginal benefit. Methodologic quality of the majority of the trials was modest.
Conclusions: Evidence from published trials suggests that Echinacea may be beneficial for the early treatment of acute URIs. The influence of publication bias on those results is unknown. Echinacea preparations vary widely in composition, and are often found in combination with other potentially active constituents, making specific dose recommendations problematic. There is very little evidence supporting the prolonged use of Echinacea for the prevention of URIs.