Long‐Term Effect of the Japanese Herbal Kampo Medicine Extracts on Renal Function: A Single Center Propensity Score Analysis

ABSTRACT Background Since the role of traditional herbal medicine for chronic kidney disease (CKD) remains uncertain, we aimed to determine the long‐term effect of Kampo extracts on renal function. Methods In this single center, retrospective observational study, records were reviewed from January 2004 to September 2024 for 234 patients with daily administration of Kampo extracts for more than 5 years. 1:1 propensity score methods were used to match Kampo cohorts. Exclusion criteria were use of diuretics except for mineralocorticoid receptor antagonists and estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m 2 . Results After propensity score matching, we identified 148 pairs of Kampo users and nonusers (mean ages 68.8 and 68.9 years, mean eGFR 68.3 and 68.2 mL/min/1.73 m 2 , respectively) including 39.9% CKD and 25.7% diabetes mellitus. Following 9 years of Kampo administration, the differences in mean eGFR slope (mL/min/1.73 m 2 /year) between Kampo users and nonusers were 1.07 (95% confidence interval [95% CI] 0.68–1.46) for all patients and 1.48 (95% CI 0.75–2.22) for CKD patients. The mean changes in eGFR (mL/min/1.73 m 2 ) from baseline to 9 years were +1.54 for Kampo users and −7.59 for nonusers (difference 9.13; 95% CI 6.14–12.13) among all patients, and among CKD patients +2.25 for Kampo users and −10.14 for nonusers (difference 12.40; 95% CI 6.99–17.80). No individual formula or formula category was independently associated with the renoprotective effect. Conclusions Long‐term administration of Kampo extracts may slow eGFR decline in patients with and without CKD, although causal conclusions cannot be drawn due to the observational and non‐randomized nature of this study.