University of Michigan
Department of Pediatrics
Evidence-Based Pediatrics Web Site

Question

• Do Echinacea root extracts have preventative effects for upper respiratory tract infections?

Clinical Bottom Lines

1. This study was unable to demonstrate a prophylactic effect of Echinacea on decreasing time to first upper respiratory infection (URI) in adults.  Also, there was no significant difference in percentage of occurrences of URI's in placebo vs. control groups.¹
2. There was a significant proportion of the population receiving Echinacea who subjectively felt that there was a positive impact on their health.

Summary of Key Evidence

1. In a three arm randomized double blind placebo-controlled trial, 302 adult volunteers were given E. angustifolia, E. purpurea, or placebo.  Population studies included European adults in military settings.  Some URI's were documented retrospectively.  The results were analyzed on the basis of intent to treat.  There were 13 patients not included in the intent to treat analysis.  The patients excluded were either accidentally unblinded or dropped out in the enrollment period.  A further 45 patients dropped out during the study, but were included in the intent to treat analysis.  In the twelve-week period, the time until occurrence of first URI was 66 days, 69 days, and 65 days respectively.  Occurrence of infection was 32%, 29.3%, and 36.7% respectively.  These differences were not statistically significant.
2. The power of the study was insufficient.  For adequate statistical power, approximately 1000 participants would have been required.

Additional Comments

• Forty-five percent of the participants had used an Echinacea product at least prior to participation in the study.  The herb has a distinct taste and likely double blinding was unsuccessful.

• A greater number of patients felt subjectively that they received a positive impact on their health in the treatment groups than in the placebo.  The reason for this could be the distinctive taste of Echinacea.  Patients who believe there is a benefit to the herb may have had a placebo effect.  Another possibility is that there was an unmeasured positive effect on health or mood.

• Study did not include pediatric population.  Further studies unlikely to be funded by small herbal pharmaceutical groups secondary to costs.

• I am not convinced that there is a beneficial effect to the use of Echinacea for prevention of URI's, but my search revealed no indication of toxicity associated with the use of the herb.  For my patients who wish to use Echinacea, I would say it is likely safe in the non-pregnant woman, and likely this can be extrapolated to treatment of children as well.  Further studies would be helpful.

Citation

1. Melchart D, Walther E, Kinde K, et al.  Echinacea root extracts for the prevention of upper respiratory tract infections.  Archives of Family Medicine 1998; 7:541-545

CAT Author: Leslie A. Caren, MD

CAT Appraisers: John Frohna, MD

Date appraised: April 19, 1999