OBJECTIVE To investigate whether Japanese Kampo medicines, including Sho-hange-kabukuryou-to, Touki-syakuyaku-san, and Hange-kouboku-to, are safe for fetuses, and whether these medicines reduce hospitalizations and medical costs in pregnant women with hyperemesis gravidarum. METHODS We used the Japan Medical Data Center database to extract data for pregnant women (aged ≥19 years) admitted to obstetric clinics or hospitals for delivery between January 1, 2005, and December 31, 2016. Eligible patients were classified into three groups: Kampo medicines for hyperemesis gravidarum, other medicines for hyperemesis gravidarum, and without hyperemesis gravidarum. Safety outcome measures were neonatal outcomes (congenital anomalies, low birthweight, and preterm birth), and effectiveness measures were mother's unplanned hospitalization for hyperemesis gravidarum and total medical costs within 20 weeks of gestation. RESULTS We identified 121 287 eligible mothers. No significant differences in the safety measures were observed among the groups. The Kampo medication group had a significantly lower proportion of mothers with unplanned hospital admission (odds ratio 0.80, 95% confidence interval [CI] 0.69-0.92) and lower total costs (coefficient [US$] 12.8, 95% CI -23.2 to -2.4) than the other medication group. CONCLUSIONS Kampo medicines may reduce unplanned admissions and medical costs among pregnant women with hyperemesis gravidarum. UMIN Clinical Trials Registry: R000037298 UMIN000032706.