Factors associated with high placebo response in clinical studies of hot flashes: a meta-analysis

Importance: High placebo response can often mask the evaluation of active treatment in clinical studies for women with hot flashes and potentially undermine the evaluation of new treatments. Objective: The aim of this meta-analysis was to determine the factors associated with high placebo response (defined as the reduction in the mean number of hot flash frequency from baseline) in randomized, controlled, double-blind studies enrolling women with hot flashes. Evidence Review: To identify eligible studies, Embase, MEDLINE, and BIOSIS Previews were searched for English-language articles published between April 1975 and August 2020. Placebo-controlled, double-blind, randomized studies that assessed changes in hot flash frequency were included if they satisfied the defined criteria. We conducted univariate and multivariate analyses using categorical and numerical data. Categorical data included the following variables and levels in brackets: active treatment type (hormone therapy /non- hormone therapy / complementary and alternative medicine), administration route (oral/non-oral), study region (in/excluded the US), breast cancer population (in/excluded), entry criteria of hot flash severity (moderate to severe only/all included), parallel or crossover study, placebo run-in period before treatment (yes/no), and menopausal status (postmenopausal only/include perimenopausal/include premenopausal). Numerical data included published year, pretreatment period duration, treatment period duration, number of sites, number of total participants, number of placebo participants, number of treatment arms, mean age, BMI, and hot flash frequency at baseline. Findings: Forty-three of the 802 identified publications were included in the review. Multivariate analysis identified three individual factors associated with high placebo response: treatment period duration, number of treatment arms, and BMI. Conclusions and Relevance: We identified several factors associated with high placebo response in clinical studies of women with hot flashes. Knowing these factors may enable proactive implementation of operational and analytic strategies that further aid in determining the true treatment effect of an intervention.