Other than methodological qualities such as allocation concealment or blinding that are known to affect the direction or magnitude of treatment effect [41, 49], we found information on placebo in PIL may be another potential factor for influencing the study outcome by possibly modulating patient expectation in the informed consent process. Therefore, further in-depth studies utilizing both qualitative and quantitative methods are warranted to better understand complicatedly intertwined factors in PILs, blinding, and outcomes of placebo-controlled trials.