Placebo Effects and the Common Cold: A Randomized Controlled Trial

Abstract

PURPOSE We wanted to determine whether the severity and duration of illness caused by the common cold are infl uenced by randomized assignment to openlabel pills, compared with conventional double-blind allocation to active and placebo pills, compared with no pills at all. METHODSWe undertook a randomized controlled trial among a population with new-onset common cold. Study participants were allocated to 4 parallel groups: (1) those receiving no pills, (2) those blinded to placebo, (3) those blinded to echinacea, and (4) those given open-label echinacea. Primary outcomes were illness duration and area-under-the-curve global severity. Secondary outcomes included neutrophil count and interleukin 8 levels from nasal wash at intake and 2 days later. RESULTSOf 719 randomized study participants, 2 were lost and 4 exited early. Participants were 64% female, 88% white, and aged 12 to 80 years. Mean illness duration for each group was 7.03 days for those in the no-pill group, 6.87 days for those blinded to placebo, 6.34 days for those blinded to echinacea, and 6.76 days for those in the open-label echinacea group. Mean global severity scores for the 4 groups were no pills, 286; blinded to placebo, 264; blinded to echinacea, 236; and open-label echinacea, 258. Between-group differences were not statistically signifi cant. Comparing the no-pill with blinded to placebo groups, differences (95% confi dence interval [CI]) were -0.16 days (95% CI, -0.90 to 0.58 days) for illness duration and -22 severity points (95% CI, -70 to 26 points) for global severity. Comparing the group blinded to echinacea 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, respectively by group, were 30 pg/mL and 1 cell for the no-pill group, 39 pg/mL and 1 cell for the group binded to placebo, 58 pg/mL and 2 cells for the group blinded to echinacea, and 70 pg/mL and 1 cell for the group with open-label echinacea, also not statistically signifi cant. Among the 120 participants who at intake rated echinacea's effectiveness as greater than 50 on a 100-point scale for which 100 is extremely effective, illness duration was 2.58 days shorter (95% CI, -4.47 to -0.68 days) in those blinded to placebo rather than no pill, and mean global severity score was 26% lower but not signifi cantly different 95% CI,. In this subgroup, neither duration nor severity differed signifi cantly between the group blinded to echinacea and the open-label echinacea group.CONCLUSIONS Participants randomized to the no-pill group tended to have longer and more severe illnesses than those who received pills. 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 fi ndings support the general idea that beliefs and feelings about treatments may be important and perhaps should be taken into consid...

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