Aims: Registries on in-hospital drug use are sparse, especially those that can be linked to nationwide registries. In this study, we present and validate the Electronic Patient Medication module (EPM)—the electronic administrative database on in-hospital drug use covering the Capital Region of Denmark. Methods: The research database (EPM-research) is an adaptation of the database underlying the electronic administrative database for in-hospital drug use (EPM-clinic). The validation study was comprised of two sub-studies. Sub-study 1: Accordance of registration between EPM-clinic and EPM-research was investigated by analyzing randomly chosen retrospective patient records. Sub-study 2: Workflows and real-life registration practices were investigated through visits to three different (two medical and one emergency) departments. An observer followed a nurse while dispensing and administering drugs. This information was compared with EPM-research. The primary endpoint for both sub-studies was accordance of generic name between registrations. Secondary endpoints were exact brand name, dose, and time of each administration. Accordance (proportions) with 95% confidence intervals (CI) using the Clopper-Pearson method were calculated. The study was approved by the Danish Data Protection Agency (BFH-2016-058-04906) and the Danish Patient Safety Authority (3-3013-1884/1/). Results: In sub-study 1 227 retrospective drug administrations were reviewed. Accordance of generic name was 100.0% (CI 98.4%−100.0%). In sub-study 2 176 drug administrations were observed of which 173 were recorded with identical generic name, resulting in 98.3% (CI 95.1%-99.6%) accordance of data. Conclusions: Our validation of the EPM-research showed very high accordance. With detailed information on in-hospital drug use, the EPM-research may be a useful tool in pharmacoepidemiological research.