Narrative Review for the Use of Kampo Medicine During Pregnancy in Japan

ABSTRACT Background Kampo medicine is commonly prescribed alongside Western pharmaceuticals. Its use during pregnancy has become increasingly common; however, there are concerns regarding safety due to the inclusion of multiple herbal components. Objective We aim to summarize the current evidence on the use and safety of Kampo medicines during pregnancy in Japan. Methods A comprehensive literature review was conducted using nine key studies, including claims database analyses and large birth cohort investigations. These were divided into two main categories: (1) studies describing the prevalence and patterns of Kampo medicine use during pregnancy, and (2) studies investigating safety outcomes such as congenital malformation, birth weight, preterm birth, hospitalization, and live birth rates. Results The proportion of pregnant women using Kampo medicines ranges from 4% to 10%, with common formulations including tokishakuyakusan, shoseiryuto, and kakkonto. Studies from both claims databases and cohort‐based self‐reports confirm widespread use. Regarding safety, multiple observational studies report no significant increase in congenital malformations, low birth weight, or preterm birth associated with Kampo medicine use. Some studies even suggest beneficial effects, such as reduced hospitalization for hyperemesis and increased live birth rates in women with recurrent pregnancy loss. However, caution is warranted for Kampo formulations containing potentially teratogenic substances such as ephedra and rhubarb. Conclusion Kampo medicine is widely used among pregnant women in Japan and appears to have a generally favorable safety profile when prescribed appropriately. Nonetheless, more rigorous prospective studies are needed to confirm safety across various Kampo formulations and patient populations.