Open-label placebo vs double-blind placebo for irritable bowel syndrome: a randomized clinical trial.

ABSTRACT: It is commonly believed that blinding to treatment assignment is necessary for placebos to have an effect. However, placebos administered without concealment (i.e., open-label placebos [OLP]) have recently been shown to be effective in some conditions. This study had two objectives: first, to determine whether OLP treatment is superior to no-pill control (NPC) in irritable bowel syndrome (IBS); and second, to compare the efficacy of OLP against double-blind placebo (DBP). In a six-week, three-arm, randomized clinical trial, participants were randomized in equal proportions to three arms: OLP, DBP or NPC. 262 adults (72.9% women), mean age 42.0 (SD=18.1) participated in the primary study. The mean improvement on the IBS Severity Scoring System (IBS-SSS) from baseline to the 6-week endpoint was significantly greater in OLP compared to NPC (90.6 vs. 52.3, p=0.038). OLP and DBP did not differ significantly on IBS-SSS improvement (100.3 vs. 90.6, p=0.485). Standardized effect sizes were moderate for OLP vs. NPC (d=.43), and small for OLP vs DBP (d=.10). Participants treated with OLP reported clinically meaningful improvements in IBS symptoms that were significantly greater than NPC. OLP and DPB had similar effects that did not differ significantly, suggesting that blinding may not be necessary for placebos to be effective, and that OLP could play a role in the management of refractory IBS patients.