Effects of echinacea on the frequency of upper respiratory tract symptoms: a randomized, double-blind, placebo-controlled trial

Ann Allergy Asthma Immunol. 2008 Apr;100(4):384-8. doi: 10.1016/S1081-1206(10)60603-5.


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).

Conclusion: Prophylactic treatment with commercially available E. purpurea capsules did not significantly alter the frequency of upper respiratory tract symptoms compared with placebo use.

Publication types

  • Randomized Controlled Trial
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Double-Blind Method
  • Echinacea / chemistry
  • Echinacea / immunology*
  • Humans
  • Middle Aged
  • Plant Preparations / immunology
  • Plant Preparations / therapeutic use*
  • Respiratory Tract Infections / immunology
  • Respiratory Tract Infections / prevention & control*


  • Plant Preparations