Echinacea is a herbaceous plant native to North America. This member of the daisy family (Asteraceae) is native to the central United States. It was widely used by the Plains Indians for a variety of indications ranging from snakebite to wound infection. Echinacea was introduced into mainstream medicine in the late 1800’s and into Europe in the early 1900’s. Today, various preparations of Echinacea enjoy widespread popularity in Europe, with over 2.4 million prescriptions written in Germany in1994. Echinacea is used for both the prevention and treatment of viral upper respiratory infections, as an adjunct to antibiotic therapy, and in the treatment of eczema, psoriasis, and herpes simplex.

The German experience with Echinacea is with dosage forms prepared from fresh above-ground portions of the plant and intended for either topical or parenteral administration. Considerable controversy exists over the relative value of orally administered Echinacea-containing products. The rationale for its use is based on its immunomodulatory effects. Echinacea does possess non-specific immunostimulatory effects. Activation of T- lymphocytes, phagocytic macrophages and natural killer cells have all been proposed as mechanisms. Increases in circulating fibroblast, beta-2 interferon and TNF have been noted in in vitro studies. Aficionados of Echinacea have suggested that its main immunostimulatory effects occur in the lymphatic tissue in the oral cavity. If this is in fact the mechanism, powdered encapsulated forms of Echinacea would not be expected to be active.

Unfortunately, there may be considerable variability in the constituents of Echinacea products. Similarly-labeled products may contain constituents of the leaf, roots or both from any one of the three most commonly harvested species (E. purpurea, E. pallida or E. angustifolia), with extraction processes ranging from cold pressing to alcohol extraction. A single active constituent has not been identified to account for the pharmacologic action of Echinacea. Standardization of dose is difficult as a result. This makes the evaluation of clinical studies a challenge, to say the least.

For a compound with as widespread a use, both in Europe and the United States, there is a paucity of well-constructed clinical trials. A computerized review of the English language literature only identified 15 citations. A literature review, published in 1994, identified 26 controlled clinical trials in the world’s literature. The authors’conclusion was that there appeared to be some evidence for an immunostimulatory effect of Echinacea. Since this review, the results of several randomized clinical trials comparing Echinacea preparations to placebo in both the prevention of viral upper respiratory tract infection and reduction in symptoms have been published.

Melchart and colleagues published the results of a randomized clinical trial comparing orally administered extracts of two Echinacea species and placebo. Three hundred two subjects, without signs or symptoms of viral upper respiratory tract illness, were entered into this three-arm trial and evaluated on an intention-to-treat basis. Time to first upper respiratory tract infection was the primary outcome measure.

Ninety-six study subjects contracted a total of 113 upper respiratory tract infections. The time to the first upper respiratory tract infection was 66 days (95% CI, 61-72 days) in those taking Echinacea angustifolia extract, 69 days (95% CI, 64-74 days) in the Echinacea purpurea subjects and 65 days (95% CI, 59-70 days) in the placebo group. There were no significant differences in the onset, severity, number or duration of upper respiratory tract infections. Interestingly, the authors administered a quality-of-life questionnaire. Although no differences were noted in this undefined questionnaire, those subjects receiving Echinacea preparations believed that they benefited from taking the medication as compared to those taking placebo.

In February of this year, Grimm and colleagues published the results of a randomized controlled trial of an extract of Echinacea purpurea. One hundred nine patients were randomized to either a standardized extract of Echinacea or placebo extract. The number and severity of colds and respiratory tract infections were noted over the 8-week duration of the study. Thirty-five of the 54 Echinacea-treated subjects and 40 of the 54 placebo-treated subjects contracted at least one cold during the trial period (Echinacea relative risk =0.88; 95% CI 0.6, 1.22). The median duration of illness was 4.5 days in the Echinacea group as compared to 6.5 days in the placebo group. The difference in the incidence of colds and the duration of illness was not statistically significant.

These most recent studies published in the US literature appear to be consistent with previous study results published in Europe. The results suggest that the administration of Echinacea at the onset of symptoms may, in some cases, reduce the duration of a common cold. The authors of Rational Phytotherapy suggest that only liquid preparations or buccal tablets should be used.

Echinacea is not, however, without negative effects. Cross-reactivity to other members of the Asteraceae family (including ragweed) is a theoretical risk. Severe allergic reactions have been noted, especially in patients with a history of asthma or allergic rhinitis. Such patients should be cautioned against consumption of Echinacea products.

Selected Bibliography:

1. Tyler VE. The Honest Herbal. A sensible guide to the use of herbs and related remedies. 3rd ed. Binghamton, NY: Pharmaceutical Products Press, 1993.

2. Schulz V, Hansel R, Tyler VE. Rational Phytotherapy. A physicians’ guide to herbal medicine. 3rd ed.Berlin Heidelberg: Springer-Verlag, 1998.

3. Melchart D, Walther E, Linde K, et al. Echinacea root extracts for the prevention of upper respiratory tract infections: A double-blind, placebo-controlled randomized trial. Arch Fam Med 1998; 7(6):541-545.

4. Grimm W, Muller H-H. A randomized controlled trial of the effect of fluid extract of echinacea purpurea on the incidence and severity of colds and respiratory infections. Am J Med 1999;106(2):138-143.