Effects of echinacea on the frequency of upper respiratory tract symptoms: a randomized, double-blind, placebo-controlled trial.
BACKGROUND
Upper respiratory tract infection symptoms are a common cause of morbidity. Herbal preparations of the plant Echinacea purpurea have immune-enhancing properties.


OBJECTIVE
To compare the frequency of upper respiratory tract symptoms in individuals receiving E. purpurea capsules and those receiving placebo to evaluate the preventive efficacy of echinacea.


METHODS
In a randomized, double-blind clinical trial, 90 volunteers recruited from hospital personnel were randomly assigned to receive 3 capsules twice daily of either placebo (parsley) or E. purpurea for 8 weeks during the winter months. Upper respiratory tract symptoms were reported weekly during this period.


RESULTS
Fifty-eight individuals were included in the final data analysis: 28 in the echinacea group and 30 in the placebo group. Individuals in the echinacea group reported 9 sick days per person during the 8-week period, whereas the placebo group reported 14 sick days (z = -0.42; P = .67). Mild adverse effects were noted by 8% of the echinacea group and 7% of the placebo group (P = .24).


CONCLUSIONS
Prophylactic treatment with commercially available E. purpurea capsules did not significantly alter the frequency of upper respiratory tract symptoms compared with placebo use.
O'Neil
Joelle
J
University of California San Francisco Fresno Family Medicine Residency, 93701-2302, USA.
Hughes
Susan
S
Lourie
Andrea
A
Zweifler
John
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D004311:Double-Blind Method; D020900:Echinacea / Q000737:chemistry / Q000276:immunology*; D006801:Humans; D008875:Middle Aged; D028321:Plant Preparations / Q000276:immunology / Q000627:therapeutic use*; D012141:Respiratory Tract Infections / Q000276:immunology / Q000517:prevention & control*
D028321:Plant Preparations