The first and most likely explanation is that the drug is too old. The focus of the IDdb is on drugs that are in research and development, so that drugs which were already widely marketed at that time the IDdb began in 1994 were not included in the database, unless they were undergoing continuing development for additional novel indications.

Another potential reason is that the drug or compound does not fit the inclusion criteria for the database. Drug development programs will be registered once they have have reached the lead optimization stage, provided there is evidence of commercial involvement. Formulations of known drugs are included only if they are considered to provide significant therapeutic advantage over existing formulations of the drug, such as improved bioavailability or a more convenient route of administration. Furthermore, imaging agents are only registered if in development for internal use.