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).

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