Current issues of ACP Journal Club are published in Annals of Internal Medicine


Therapeutics

Review: Heterogeneous studies show that Echinacea may be effective for preventing and treating the common cold

ACP J Club. 1999 July-Aug;131:19. doi:10.7326/ACPJC-1999-131-1-019


Source Citation

Melchart D, Linde K, Fischer P, Kaesmayr J. Echinacea for the prevention and treatment of the common cold. Cochrane Review, latest version 16 November 1998. In: The Cochrane Library. Oxford: Update Software.


Abstract

Question

Are Echinacea extracts effective for preventing and treating the common cold?

Data sources

Studies were identified by searching MEDLINE (1966 to 1998), EMBASE/Excerpta Medica (1991 to 1998), the Cochrane Acute Respiratory Infections Review Group and Complementary Medicine Field databases, and Phytodok (Munich) with the truncated term Echinac; bibliographies of relevant articles; and proceedings of phytomedicine congresses. Manufacturers and researchers in the field were contacted.

Study selection

Studies were selected if they were randomized or quasi-randomized trials of Echinacea extracts for preventing or treating unspecific viral upper respiratory tract infections (URTIs).

Data extraction

Independent reviewers assessed the quality of study methods and extracted data on participants, methods, interventions, outcomes, results, dropouts, and side effects. Authors and manufacturers were contacted to obtain additional information.

Main results

16 studies (n = 3396) met the inclusion criteria. 5 heterogeneous, placebo-controlled prevention studies (n = 1272) with acceptable methodologic quality compared different Echinacea preparations with placebo. 2 of these studies showed a lower incidence of infection for Echinacea than for placebo (relative risk reductions [RRRs] 33%, 95% CI 3% to 54%; and 49%, CI 22% to 67%), and 3 showed a trend in favor of the treatment group (RRRs 12%, CI -13% to 32%; 14%, CI -2% to 28%; and 16%, CI -18% to 41%). 3 additional prevention studies with a no-treatment control group and quasi-random allocation (n = 1139) showed that Echinacea combined with other herbs led to a greater reduction in URTI in children than did no treatment (weighted RRR 42%, CI 19% to 58% { P < 0.001}*). 8 heterogeneous treatment studies (n = 985) compared different Echinacea preparations with placebo; only 1 study had a clearly predefined main outcome measure. In 5 of these trials, Echinacea was more effective than placebo for reducing the duration of illness, improving symptom scores, or reducing the incidence of running nose. 1 trial had statistically significant results for a subgroup only, and 2 trials found no difference between Echinacea and placebo.

Conclusions

Heterogeneous studies used different preparations of Echinacea extracts and show that Echinacea may be effective for treating and preventing the common cold. More rigorous studies are needed to determine which preparations are most effective.

Sources of funding: Karl und Veronica Carstens Foundation; National Institute for Arthritis and Musculoskeletal and Skin Diseases; Erich Rothenfusser Foundation.

For correspondence: Dr. K. Linde, Münchener Modell—Centre for Complementary Medicine Research, Technical University/Ludwig-Maximilians-University, Kaiserstrasse. 9, Munich 80801, Germany. FAX 49-89-393484.

* P value calculated from data in article.


Commentary

The common cold is the most common viral infection and is the main cause of absence from work or school. In the United States, the incidence in children and adults is 6 to 8 and 2 to 3 infections per person-year, respectively (1). Bacterial infections (mainly otitis media or sinusitis) may complicate about 3% to 4% of cases (1). An effective cure would therefore be of great importance.

Patients with a common cold do not usually consult family physicians until they have been ill for ≥ 3 days, which is when they may have possible bacterial complications or need sick leave. Most nonantibiotic medications, such as zinc lozenges, ipratropium, colostrum, and Echinacea preparations, are provided over the counter.

Melchart and colleagues' meta-analysis evaluates the effect of Echinacea preparations. Most of the available studies report positive results for prevention or reduction of illness duration, symptom scores, or running nose. However, the studies have several methodologic weaknesses: They are heterogeneous, they do not define disease, and the outcome measures lack validity and reliability. Moreover, Echinacea products on the market differ more in their biochemical composition than do other plant extracts because different Echinacea species, plant parts, and extraction methods are used. Thus, the results from the trials may not apply to the product that a person receives. Publication bias may also exist.

In 4 of the 5 placebo-controlled prevention studies, participants used Echinacea daily for 8 to 12 weeks. The 5th study was a combination of prevention and treatment because therapy with the medication began at the onset of symptoms. The prevention studies in children showed a 23% absolute reduction in incidence with daily use for 6 weeks, which results in a number needed to treat of 5. Side effects were similar for Echinacea and placebo.

What would I recommend to patients? I would say that Echinacea might have a moderate effect in the treatment of the common cold. It may shorten the duration of illness by 1 to 3 days and may reduce symptoms. 5 patients must use Echinacea for several weeks to prevent 1 additional episode of the common cold. Medication is probably most effective when therapy is started at symptom onset.

Morten Lindbaek, MD, PhD
University of OsloOslo, Norway


Reference

1. Gwaltney JM Jr. Rhinoviruses. In: Evans AS, Kalow RA, eds. Viral Infections of Humans: Epidemiology and Control. 4th ed. New York: Plenum; 1997.