Heterogeneity of placebo effects on urinary incontinence in overactive bladder syndrome: A meta‐analysis of Japanese placebo‐controlled clinical trials

Objectives The effect sizes, changes over time, and heterogeneity of placebo effects on frequency of urination for voiding disorders in Japanese clinical trials have been published. This study evaluated the characteristics of placebo effects on overall and urge incontinence in overactive bladder patients. Methods A meta‐analysis of Japanese placebo‐controlled clinical trials was conducted to determine placebo effects on the daily frequency of overall ( n = 16) and urge ( n = 11) incontinence and identify factors that should be considered in clinical trials. Results The between‐study heterogeneity variance of placebo effects for overall and urge incontinence at 8 weeks was estimated as I 2 = 70.3% and 64.2%, and the prediction interval for the ratio of means ranged from g = 0.31–0.91 and 0.32–0.81, respectively. Subgroup analysis using the random‐effects model showed placebo effects in overall incontinence ( p = 0.08) and urge incontinence ( p < 0.0001). The ratio of means (95% confidence interval) of urge incontinence frequency from baseline to 4 ( n = 10), 8 ( n = 10), and 12 ( n = 7) weeks were 0.65 (0.57, 0.74), 0.51 (0.42, 0.62), and 0.48 (0.36, 0.64), respectively, for the random‐effects model. Regression analysis did not reveal any significant factors that influenced placebo effects. Conclusions This meta‐analysis confirmed the characterization of placebo effects on overall and urge incontinence, which demonstrates heterogeneity between trials. The impact of population, follow‐up period, and endpoints on placebo effects should be considered when designing clinical trials for overactive bladder syndrome.