The common cold is characterized by upper respiratory symptoms and caused by many different viruses. An effective treatment for community-acquired colds has not been discovered yet. Preparations and extracts from echinacea plants are widely used, with many scientific studies noting clinical benefits. Randomized controlled studies looking at preventive or treatment benefits of echinacea have noted varying results. The highest-quality study looking at prevention noted a 10 to 15 percent reduction in relative risk. The treatment studies have demonstrated reductions in symptom severity and duration, but these studies had major limitations that potentially affected the conclusions. Barrett and associates conducted a randomized, double-blind, placebo-controlled, community-based trial to measure the efficacy of encapsulated whole-plant echinacea preparations used early in the course of a cold.

Undergraduate student participants with early cold symptoms were randomly assigned to receive the trial treatment or placebo. Each participant was instructed to take 1 g of echinacea six times on the first day, followed by1 g three times daily on subsequent days until symptoms resolved or for a maximum of 10 days. Prospective participants who had symptoms for more than 36 hours or were using some other agent to treat their cold symptoms were excluded. Primary outcomes included severity and duration of self-reported symptoms, with all participants completing a daily self-assessment.

Of 148 enrolled participants, 142 completed the protocol. Overall adherence was 92 percent based on pill counts. There was no detectable difference in cold duration or symptom severity between the echinacea and placebo groups. Adverse effects also were not significantly different between the two groups.

The authors conclude that there is no benefit in using echinacea to treat common cold symptoms. This result is contrary to results of other studies that have shown some positive effects. More studies are needed to provide a final answer about the efficacy of echinacea in common cold treatment.

In an editorial in the same journal, Turner points out the difficulty in evaluating plant products because of variability in the phytochemical compositions between preparations and even among varying lots from the same manufacturer. The active ingredient, mechanism of action, dosing, pharmacokinetics, and bioavailability remain to be defined. To be more convincing, future studies will need to scientifically characterize the substance being used and the way the substance is affecting pathophysiologic processes.

editor's note: Alternative and complementary treatments are becoming more mainstream, and physicians need to know about regimens in common use. Echinacea is one of the most frequently used herbs in the Western world and is considered to be an enhancer of the immune system. American Family Physician initiated a series on alternative and complementary medicine with an article on echinacea (Kligler B. Echinacea. Am Fam Physician 2003;67:77–80,83). In this article, Kligler points out the lack of data supporting a positive prophylactic effect and the modest data demonstrating a positive treatment effect of echinacea in upper respiratory infections. Adverse effects are rare, and dosing depends on the specific preparation used. Kligler concludes that the lack of standardization of echinacea products makes its use difficult, but patients who choose this treatment for their upper respiratory symptoms can be supported in their decision. Better constructed trials are needed to provide a definitive recommendation. A Cochrane review of the efficacy of echinacea in the management of the common cold, last updated in 1998, supports these conclusions.—r.s.