A randomized controlled trial of the effect of fluid extract of Echinacea purpurea on the incidence and severity of colds and respiratory infections.

PURPOSE: Fluid extracts of Echinacea purpurea are widely used for the prevention and treatment of colds and respiratory infections, although the clinical efficacy of this agent has not been proven.

PATIENTS AND METHODS: A total of 109 patients with a history of more than 3 colds or respiratory infections in the preceding year were randomly assigned to receive 4 mL fluid extract of Echinacea purpurea or 4 mL placebo-juice twice a day in a double-blind manner. (One patient withdrew his consent before taking the first dose of the allocated medication; thus, only 108 patients were included for analysis.) The incidence and severity of colds and respiratory infections were determined during 8 weeks of follow-up, based on patient reported symptoms together with findings on physical exam. The severity of each infection was graded by the investigators. Relative risks (RR) and 95% confidence intervals (CI) were estimated.

RESULTS: During the 8-week treatment period, 35 (65%) of 54 patients in the Echinacea group and 40 (74%) of 54 patients in the placebo group had at least one cold or respiratory infection [RR = 0.88; 95% CI (0.60, 1.22)]. The average number of colds and respiratory infections per patient was 0.78 in the Echinacea group, and 0.93 in the placebo group [difference = 0.15; 95% CI (-0.12, 0.41), P = 0.33]. Median duration of colds and respiratory infections was 4.5 days in the Echinacea group and 6.5 days in the placebo group (95% CI: -1, +3 days; P = 0.45). There were no significant differences between treatment groups in the number of infections in each category of severity. Side effects were observed in 11 patients (20%) of the Echinacea group and in seven patients (13%) of the placebo group (P = 0.44).

CONCLUSION: Treatment with fluid extract of Echinacea purpurea did not significantly decrease the incidence, duration or severity of colds and respiratory infections compared to placebo.