Safety of herbal medicine decoction for facial palsy: Coarsened exact matching analysis of the national health insurance database

Background: Herbal medicine decoctions (HMD) are potential treatments for Bell's palsy (BP), but real-world evidence regarding the safety is limited. This study investigated whether HMD use for BP was associated with risk of adverse events using a nationwide claims-based database in South Korea. Methods: This retrospective cohort study used data from the Korean Health Insurance Review and Assessment database. We applied coarsened exact matching, through which 1627 BP patients who received at least one HMD prescription between November 2020 and February 2022 were matched with 1627 BP patients who did not use HMD. Difference-in-differences logistic regression modeling compared the incidences of safety outcomes between HMD users and non-users. Results: No significant differences were observed in the risk of hepatotoxicity, renal failure, allergic events, hospitalization, and emergency department visits between HMD users and non-users with BP, assessed at 3, 6, 9 and 11 months after HMD prescription. All effect estimates and corresponding 95 % confidence intervals included the null value. Conclusions: There was no significant difference in the risk of safety outcomes between HMD users and non-users with BP. Further research is warranted to understand the safety of specific herbal formulas or individual herbs using broader safety measures.