Am Fam Physician. 2011;84(9):1050-1057
Background: Echinacea is believed to enhance immune response by macrophage activation and cytokine expression; however, its effectiveness at treating the common cold remains debatable. Although early industry- sponsored trials reported statistically significant benefits, subsequent randomized trials, reviews, and meta-analyses have yielded conflicting results. Barrett and colleagues conducted a randomized controlled trial to determine the benefits of echinacea as a treatment for the common cold.
The Study: A total of 719 patients with cold symptoms were randomized to one of four study groups: no treatment, placebo (blinded), echinacea (blinded), or echinacea (unblinded). The type of echinacea used was a root-based, alkamide-rich preparation containing the equivalent of 675 mg of Echinacea purpurea root and 600 mg of Echinacea angustifolia root, each standardized to 2.1 mg of alkamides, which is believed to be more effective than the nonroot portions of echinacea.
Eligible patients had developed at least one cold symptom (i.e., nasal discharge, nasal obstruction, sneezing, or sore throat) within 36 hours of enrollment. Patients receiving other upper respiratory treatments (e.g., antibiotics, vitamin supplements, nonprescription cold treatments) were excluded, as were patients with a history of allergic rhinitis or asthma. The primary outcome was global severity, with duration and symptom severity assessed twice daily. Secondary outcomes included self-report on psychosocial questionnaires and biomarkers of immune response and inflammation.
Results: Both echinacea groups had lower mean severity scores than the control groups, although this did not reach statistical significance. Mean illness duration was also shorter in the echinacea groups (6.34 versus 6.76 days for the blinded and unblinded groups, respectively) than in the control groups (6.87 versus 7.03 days for placebo and no-pill groups, respectively). However, this was not statistically significant. A subgroup analysis of patients enrolled within 24 hours of their first symptoms showed similar, albeit nonsignificant, trends for lower severity and illness duration in the echinacea groups. Immune response markers (i.e., nasal neutrophil counts and interleukin-8 levels in nasal wash) also increased faster in the echinacea groups, but this was not statistically significant. Adherence rates and the incidence of adverse effects were similar across all groups.
Conclusion: Although there were trends toward decreased illness severity, decreased duration, and enhanced immune response among patients treated with echinacea, they did not reach statistical significance. The effect was not large, amounting to about half a day's reduction in illness duration and a 10 percent reduction in overall illness severity. The authors conclude that it is likely that echinacea has only a small beneficial effect in persons with the common cold.