Placebo Effects Modest in Treating the Common Cold

Laurie Barclay, MD

July 11, 2011

July 11, 2011 — Placebo effects are modest in treating patients with the common cold, according to the results of a parallel-group, randomized controlled trial reported in the July/August issue of the Annals of Family Medicine.

"We wanted to determine whether the severity and duration of illness caused by the common cold are influenced by randomized assignment to open-label pills, compared with conventional double-blind allocation to active and placebo pills, compared with no pills at all," write Bruce Barrett, MD, PhD, from the University of Wisconsin, Madison, and colleagues.

In this study, 719 participants with new-onset common cold were randomly assigned to 1 of 4 groups. Patients in group 1 received no pills, those in group 2 were blinded to placebo, those in group 3 were blinded to echinacea, and those in group 4 received open-label echinacea. Illness duration and global severity (measured by area under the curve) were the main study endpoints, and neutrophil count and interleukin 8 levels from nasal wash at enrollment and 2 days later were secondary endpoints.

Two of the randomized participants were lost to follow-up, and 4 left the study early. Age range was 12 to 80 years, 64% were women, and 88% were white. Participants randomly assigned pills reported colds that were on average 0.16 to 0.69 days shorter and 8% to 17% less severe than the colds of patients in the no-pill group. Mean illness duration was 7.03 days in the no-pill group, 6.87 days in the group blinded to placebo, 6.34 days for the group blinded to echinacea, and 6.76 days for those receiving open-label echinacea.

There were no statistically significant between-group differences in mean global severity scores. For the no-pill group compared with the blinded to placebo group, differences were −0.16 days (95% confidence interval [CI], −0.90 to 0.58 days) for illness duration and −22 severity points (95% CI, −70 to 26 points) for global severity. For the group blinded to echinacea compared with the open-label echinacea group, differences were 0.42 days (95% CI, −0.28 to 1.12 days) and 22 severity points (95% CI, −19 to 63 points). Median change in interleukin 8 concentration and neutrophil cell count were not statistically significantly different between groups.

There were 120 participants who at enrollment rated the efficacy of echinacea as greater than 50 on a 100-point scale (on which 100 represented extremely effective). In this subgroup, illness duration was 2.58 days shorter (95% CI, −4.47 to −0.68 days) in those blinded to placebo compared with no pill, and mean global severity score was 26% lower, but this was not a significant difference (−97.0 points; 95% CI, −249.8 to 55.8 points). In this subgroup, duration and severity were not significantly different between the group blinded to echinacea and the open-label echinacea group.

Limitations of this study include those related to statistical testing and interpretation of multiple outcomes, and changing expectations over time regarding the efficacy of echinacea, which may have influenced the placebo effect of echinacea.

"Participants randomized to the no-pill group tended to have longer and more severe illnesses than those who received pills," the study authors write. "For the subgroup who believed in echinacea and received pills, illnesses were substantively shorter and less severe, regardless of whether the pills contained echinacea. These findings support the general idea that beliefs and feelings about treatments may be important and perhaps should be taken into consideration when making medical decisions."

The National Center for Complementary and Alternative Medicine at the National Institutes of Health sponsored this study. Dr. Barrett was supported by the National Center for Complementary and Alternative Medicine and by the Robert Wood Johnson Foundation Generalist Physician Faculty Scholars Program. Leadership at the University of Wisconsin School of Medicine and Public Health provided resources to complete the project when funds ran out. The Australian firm MediHerb provided the echinacea and placebo tablets used in this trial.

Ann Fam Med. 2011;9:312-322.