Real-world data (RWD), such as a health insurance claim database and electronic medical record database, which records daily medical care information, is one of the most important data sources in pharmacoepidemiological studies. In Japan, a post-marketing database study has been added as a new category of post-marketing surveillance since April 2018. It is expected that the post-marketing database studies will be conducted in the actual risk management plan； however, at this point, few have reached the stage of publishing study results. On the other hand, overseas, many database research results using RWD have already been reported. Although it is necessary to keep in mind that there are differences in the characteristics of the databases (e.g., data contents, structures) and the differences in the medical environment between overseas and Japan, we think that critically reviewing these reports has a reference value for the planning, execution, and interpretation of the results in performing post-marketing database studies in Japan. The purpose of this report is to examine the characteristics and cautions of the database studies through a critical review of published articles of overseas RWD studies and to make recommendations that are useful for conducting post-marketing database studies in Japan. We hope this article will become a help in the planning and implementation of future post-marketing database studies.