Structural Characteristics of Research Ethics Committees in Japan and Their Relevance to Regulatory Science: A Nationwide Descriptive Study

Background Research ethics committees (RECs) and institutional review boards (IRBs) provide independent ethical and scientific oversight of health-related research. In Japan, the Pharmaceuticals and Medical Devices Agency (PMDA) increasingly conducts regulatory science (RS) research, which aims to generate scientific evidence to support regulatory decision-making. However, nationwide REC/IRB structures in Japan, and their alignment with the needs of RS oversight, have not been described. Methods We conducted a nationwide cross-sectional descriptive study using publicly available data from the Research Ethics Review Committee Reporting System of Japan (June 5, 2024). Committee size, gender composition, and members’ professional expertise were analyzed by institution type. We compared these findings with structural requirements in Japanese regulations and guidelines. In addition, we conducted a complementary literature-based analysis of PMDA-affiliated RS research using PubMed. Major Medical Subject Headings (MeSH) terms were examined to identify dominant research areas and to contextualize the REC/IRB structure within the current landscape of RS research. Results A total of 2,604 RECs/IRBs comprising 26,786 members were identified nationwide. The mean committee size was 10.3, exceeding the minimum requirements specified in Japanese regulations. Overall, committees commonly included multiple lay members, with 68.0% of institutions having at least two public representatives. In contrast, a substantial gender imbalance was observed, with 70.1% of committee members being male across all institutional categories. Committee composition varied by institution type. Analysis of MeSH terms in PMDA-affiliated RS research publications showed frequent focus on regulatory review, pharmacovigilance, advanced biomedical technologies, and clinical trial methodology. Conclusions Japanese RECs/IRBs generally exceed minimum structural requirements, including the inclusion of lay members, while gender representation appears uneven. Variations in committee composition reflected institutional differences in research characteristics. In the context of RS research, REC/IRB structures that incorporate relevant expertise alongside diverse perspectives may help inform discussions on ethical review practices.