Echinacea May Be No More Effective Than Placebo for the Common Cold

Laurie Barclay, MD

December 20, 2010

December 20, 2010 — Echinacea may be no more effective than placebo for treatment of the common cold, according to the results of a randomized controlled trial reported in the December 21 issue of the Annals of Internal Medicine.

"Echinacea is a popular nonprescription treatment for the common cold," write Bruce Barrett, MD, PhD, from the University of Wisconsin in Madison, and colleagues. "The efficacy of echinacea in this regard continues to be debated after hundreds of studies."

The study goal was to evaluate the potential benefits of echinacea to treat patients with the common cold. In Dane County, Wisconsin, 719 patients, aged 12 to 80 years, with new-onset common cold were randomly assigned to 1 of 4 parallel groups. Patients in these groups received no pills, placebo pills in blinded fashion, echinacea pills in blinded fashion, or echinacea pills in unblinded, open-label fashion. In the echinacea groups, patients were given the equivalent of 10.2 g dried echinacea root during the first 24 hours and 5.1 g daily for the next 4 days, whereas patients in the placebo group received indistinguishable tablets containing only inert ingredients.

The main study endpoint was the area under the curve for global severity, and secondary endpoints were interleukin 8 levels and neutrophil counts from nasal wash, measured at study entry and 2 days later. The Wisconsin Upper Respiratory Symptom Survey, short version, was used twice daily to determine severity based on self-report.

The study protocol was completed by 713 of the 719 patients enrolled, of whom 64% were women and 88% were white. Mean age was 33.7 years. Mean global severity was 236 for the blinded echinacea group, 258 for the unblinded echinacea group, 264 for the blinded placebo group, and 286 for the no-pill group.

There was a nonsignificant, 28-point trend toward benefit for echinacea between the 2 blinded groups (95% confidence interval [CI], −69 to 13 points; P = .089). In the blinded and unblinded echinacea groups, mean illness duration was 6.34 and 6.76 days, respectively, vs 6.87 days in the blinded placebo group and 7.03 days in the no-pill group.

In the blinded groups, there was a nonsignificant benefit of echinacea (0.53 day; 95% CI, −1.25 to 0.19 days; P = .075). There was no statistically significant difference in median change in interleukin 8 levels and neutrophil counts (30 ng/L and 1 cell/high-power field [hpf] in the no-pill group, 39 ng/L and 1 cell/hpf in the blinded placebo group, 58 ng/L and 2 cells/hpf in the blinded echinacea group, and 70 ng/L and 1 cell/hpf in the open-label echinacea group).

Limitations of this study included lack of generalizability to other geographic areas or racial/ethnic groups, lack of diagnostic confirmation of the causal virus, and higher-than-expected variability, resulting in limited power to detect small benefits. In addition, the findings could not be generalized to other echinacea formulations or doses.

"Illness duration and severity were not statistically significant with echinacea compared with placebo," the study authors write. "These results do not support the ability of this dose of the echinacea formulation to substantively change the course of the common cold."

The National Center for Complementary and Alternative Medicine, National Institutes of Health, supported this study, along with a Patient-Oriented Career Development Grant and the Robert Wood Johnson Foundation Generalist Physician Faculty Scholars Program. MediHerb provided the placebo and echinacea tablets used in this trial and conducted the phytochemical assays, all free of charge. Disclosures of the study authors can be viewed on the journal's Web site.

Ann Intern Med. 2010;153:769-777.