Echinacea root extracts for the prevention of upper respiratory tract infections: a double-blind, placebo-controlled randomized trial.
OBJECTIVE
To investigate the safety and efficacy of 2 extracts of echinacea for preventing upper respiratory tract infections.


METHODS
Three-armed, randomized, double-blind, placebo-controlled trial.


METHODS
Four military institutions and 1 industrial plant.


METHODS
Three hundred two volunteers without acute illness at time of enrollment.


METHODS
Ethanolic extract from Echinacea purpurea roots, Echinacea angustifolia roots, or placebo, given orally for 12 weeks.


METHODS
Time until the first upper respiratory tract infection (time to event). Secondary outcome measures were the number of participants with at least 1 infection, global assessment, and adverse effects.


RESULTS
The time until occurrence of the first upper respiratory tract infection was 66 days (95% confidence interval [CI], 61-72 days) in the E angustifolia group, 69 days (95% CI, 64-74 days) in the E purpurea group, and 65 days (95% CI, 59-70 days) in the placebo group (P = .49). In the placebo group, 36.7% had an infection. In the treatment groups, 32.0% in the E angustifolia group (relative risk compared with placebo, 0.87; 95% CI, 0.59-1.30) and 29.3% in the E purpurea group (relative risk compared with placebo, 0.80; 95% CI, 0.53-1.31) had an infection. Participants in the treatment groups believed that they had more benefit from the medication than those in the placebo group (P = .04). Adverse effects were reported by 18 subjects in the E angustifolia group, 10 in the E purpurea group, and 11 in the placebo group.


CONCLUSIONS
In this study a prophylactic effect of the investigated echinacea extracts could not be shown. However, based on the results of this and 2 other studies, one could speculate that there might be an effect of echinacea products in the order of magnitude of 10% to 20% relative risk reduction. Future studies with much larger sample sizes would be needed to prove this effect.
Melchart
D
D
Center for Complementary Medicine Research, Technische Universität, Munich, Germany. Muenchener.Modell@lrz.uni-muenchen.de
Walther
E
E
Linde
K
K
Brandmaier
R
R
Lersch
C
C
D000328:Adult; D004311:Double-Blind Method; D005260:Female; D005858:Germany; D006801:Humans; D008297:Male; D008875:Middle Aged; D008517:Phytotherapy; D010936:Plant Extracts / Q000627:therapeutic use; D018517:Plant Roots / Q000627:therapeutic use; D010946:Plants, Medicinal / Q000009:adverse effects / Q000627:therapeutic use*; D012141:Respiratory Tract Infections / Q000517:prevention & control*; D013997:Time Factors; D016896:Treatment Outcome; D014838:Volunteers
D010936:Plant Extracts