Objectives: This study aimed to assess the effect sizes, changes over time, and ethnic differences in placebo effects on urinary function among Japanese patients participating in clinical trials.
Methods: A meta-analysis of 30 Japanese placebo-controlled clinical trials was conducted to determine the placebo effects on three functions: daily urinary frequency, nocturnal urinary frequency, and average urine volume per void.
Results: The I-square heterogeneity values for the basic values of the three functions ranged from 84.5% to 97.9%, with differences among trials. Longitudinal analysis (1 to 12 weeks) indicated an enhanced placebo effect for up to 8 weeks and no consistency among trials on nocturnal urinary frequency (p < 0.01), unlike those on daily urinary frequency and average urine volume per void (p = 1.0). Based on the random-effects model, the mean differences in urinary frequency at 4, 8, and 12 weeks were -0.70 (-0.80; -0.60), -1.06 (-1.16; -0.96), and -1.18 (-1.34; -1.01), respectively. Furthermore, the mean difference (95% confidence interval) in nocturnal urinary frequency and volume of urination per void at 12 weeks was -0.63 (-0.94; -0.31) and 9.67 (7.25; 12.1), respectively.
Conclusions: My findings suggest an increase in the strength of placebo effects over time (up to 8 weeks). A comparison of my results to those published in previous global reports showed no meaningful differences in placebo effects among ethnic groups. The consistent placebo effect size on urinary function could be an external indicator in clinical trials.
Keywords: Japan; ethnicity; overactive urinary bladder; placebo effect; urination.
© 2023 The Japanese Urological Association.