Comparison of Labeled Dosages Between Japan and the United States for Drugs Approved in Japan from 2020 to 2025

Abstract Introduction Although approved doses in Japan have generally been lower than in Western countries, these differences have been diminished with global drug development. Studies evaluating dose differences between Japan and the United States (US) using post-2010 data are limited, and none have focused on the 2020s. Methods This study characterized labeled dosage differences between Japan and the US for new molecular entities approved during 2020 – 2025. Major differences were defined as a ≥2-fold difference in the maintenance or maximum dose; all others were classified as minor differences. Results Of 187 comparable drugs, 38 (20.3%) had dosage differences between Japan and the US: seven drugs (3.7%) showed major differences (three with higher doses in Japan and four with higher doses in the US), and 31 drugs (16.6%) showed minor differences. Common minor differences included initial-dose differences and body weight-based subgroup differences. Nervous system drugs showed the highest proportion of dosage differences (50.0%), followed by alimentary tract and metabolism (31.3%) and cardiovascular system drugs (22.2%). In contrast, dermatological (11.1%), antineoplastic (10.7%), and systemic anti-infective drugs (8.3%) showed lower proportions. No large differences were observed across assessed factors such as dosing types (fixed dose, per body weight) and administration routes. Conclusions Approximately 20% of drugs approved in Japan during 2020 – 2025 had dosage differences from those in the US. The proportion of drugs with dosage differences varied across therapeutic areas. Only 3.7% had major differences. These findings may reflect progress in the international harmonization of labeled drug dosages between Japan and the US.