The drug interaction database system was originally developed at Songklanagarind Hospital. Data sets of drugs available in Songklanagarind Hospital comprising standard drug names, trade names, group names, and drug interactions were set up using Microsoft® Access 2000. The computer used was a Pentium III processor running at 450 MHz with 128 MB SDRAM operated by Microsoft® Windows 98. A robust structured query language algorithm was chosen for detecting interactions. The functioning of this database system, including speed and accuracy of detection, was tested at Songklanagarind Hospital and Naratiwatrachanagarind Hospital using hypothetical prescriptions. Its use in determining the incidence of drug interactions was also evaluated using a retrospective prescription data file. This study has shown that the database system correctly detected drug interactions from prescriptions. Speed of detection was approximately 1 to 2 seconds depending on the size of prescription. The database system was of benefit in determining of incidence rate of drug interaction in a hospital.