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SELECTION CRITERIA: Published or unpublished reports of all blinded placebo-controlled randomized trials of any Echinacea formulation used as a treatment or for the prevention of URIs.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.
Clinical question
Are orally ingested Echinacea extracts effective in reducing the incidence, severity, or duration of acute upper respiratory infections?
Upper respiratory infection (URI), usually viral, with its common variants rhinosinusitis and pharyngitis, is the highest-incidence acute illness in the developed world.1-3 According to estimates, the average adult in the United States has 2 to 4 colds per year; the average schoolchild has 6 to 10.4 Although patients with complications, such as bacterial sinusitis, otitis media, streptococcal pharyngitis, bronchospasm, or pneumonia may benefit from antibiotic or inhaler treatment, medical science has little to offer for uncomplicated infections.5-10 Nevertheless, antibiotics are frequently prescribed, despite convincing evidence of little or no benefit.11-17 Clearly, there is great need for effective, safe, and affordable treatment.
Botanical extracts from plants of the genus Echinacea are among the most widely used herbal medicines throughout Europe and North America and are most commonly used for the prevention or treatment of URIs. Echinacea extracts are believed to affect URIs through “immunostimulating” activity. Symptom reduction through immunomodulation holds some theoretical and empirical promise.18,19 If effective, such treatment could have an impact on the morbidity and loss of productivity associated with URIs, and the overuse of antibiotics and the effects of their sequelae in terms of costs, adverse effects, and antibiotic resistance.
Background
Echinacea was first used by Native Americans as a remedy for a wide variety of illnesses. It was mentioned in the Flora Virginica in 1762, the Eclectic Dispensatory of the United States of America in 1852, and the National Formulary of the United States from 1916 until 1950.20,21 A 1909 editorial in the Journal of the American Medical Association stated that Echinacea was “deemed unworthy of future consideration,” and it subsequently fell into many decades of disuse in the United States.22 In Europe, however, Echinacea grew in popularity from its introduction in the 1920s to the present. Extracts from the leaves, flowers, and roots of Echinacea purpurea and its cousins E pallida and E angustifolia are currently sold under hundreds of brand names throughout Europe and North America. In Germany, Echinacea has been approved by the German regulatory Commission E for treating respiratory and urinary tract infections.23 More than 3 million physician prescriptions for Echinacea preparations are written each year.24,25 More than 400 scientific studies, mostly German, have detailed Echinacea’s botany, chemistry, pharmacology, and clinical effects.26-29
In the United States, perhaps because of the regulatory climate,30 herbal medicines are usually used without the advice or knowledge of a physician. Although precise estimates of the scope of Echinacea use in the United States are not available, several indicators point toward a large and growing pattern of use. Eisenberg and colleagues,31 using a randomized national telephone survey, estimated that in 1990 34% of Americans had used some type of unconventional medicine, and 10% had seen a provider of herbal therapy. Using the same methods, these researchers32 put the 1997 estimates at 42% and 15%, respectively. Another randomized national telephone survey in 1997 estimated that 17% of Americans used some type of herbal therapy.33 A Gallup poll in 1997 estimated that 32% of Americans used herbal medicines, and a Harris poll in 1998 placed the figure at 37%.34 According to recent market surveys, Americans spend close to $4 billion a year on herbal supplements.34 Several surveys have indicated that Echinacea preparations are the leading botanical medicines in the United States, with close to 10% of the total herbal market.34,35 Given its current popularity and reputation as scientifically justified, Echinacea will likely continue to be widely used.