The huge number of drug interactions makes it impossible to memorize them all. Detecting them and preventing adverse effects requires the use of reference works or databases. There are numerous discordances between the so-called "reference" books and databases. Nonexistent and unconfirmed interactions are published. The wording of the "drug interactions" section of the summary of product characteristics (SCP) sometimes sheds very little light on the risks involved. The delay by AFSSAPS in updating its drug interaction thesaurus may present problems in clinical practice. It is essential to know the limitations of the computerized systems for detecting and reporting drug interactions.