Ann Intern Med. 2002 Dec; 137(12): 939-46.

Treatment of the common cold with unrefined echinacea. A randomized, double-blind, placebo-controlled trial.

Barrett BP, Brown RL, Locken K, Maberry R, Bobula JA, D'Alessio D.

Department of Family Medicine, University of Wisconsin-Madison, 777 South Mills, Madison, WI 53715, USA.

BACKGROUND: Echinacea preparations are widely used to treat the common cold. OBJECTIVE: To assess the efficacy of dried, encapsulated, whole-plant echinacea as early treatment for the common cold. DESIGN: Randomized, double-blind, placebo-controlled community-based trial. SETTING: University of Wisconsin-Madison, Madison, Wisconsin. PARTICIPANTS: 148 registered students with common colds of recent onset. INTERVENTION: An encapsulated mixture of unrefined Echinacea purpurea herb (25%) and root (25%) and E. angustifolia root (50%) taken in 1-g doses six times on the first day of illness and three times on each subsequent day of illness for a maximum of 10 days. MEASUREMENTS: Severity and duration of self-reported symptoms of upper respiratory tract infection. RESULTS: No statistically significant differences were detected between the echinacea and placebo groups for any of the measured outcomes. Trajectories of severity over time were nearly identical in the two groups. Mean cold duration was 6.01 days in both groups as a whole, 5.75 days in the placebo group, and 6.27 days in the echinacea group (between-group difference, -0.52 day [95% CI, -1.09 to 0.22 days]). After controlling for severity and duration of symptoms before study entry, sex, date of enrollment, and use of nonprotocol medications, researchers found no statistically significant treatment effect (adjusted hazard ratio, 1.24 [CI, 0.86 to 1.78]). Multivariable regression models assessing severity scores over time failed to detect statistically significant differences between the echinacea and placebo groups. CONCLUSION: Compared with placebo, unrefined echinacea provided no detectable benefit or harm in these college students who had the common cold.