The information about a drug interaction is specified as a section which should be printed on the package insert in Japan, the U.S. and the U.K. In Japan, the information on drug metabolizing enzymes is described in the precautions for use in the package insert of many pharmaceutical agents following the incidence of the harmful effects of sorivudine. Since many elderly people suffer from two or more diseases as a result of aging and multiple pharmaceuticals are prescribed for them, the risk of drug interactions is increased. The therapeutic category where the most statements regarding drug metabolizing enzyme were in the package inserts, is hypnotics and sedatives, and anxiolytics; 100 out of 306 drugs include a statement about drug metabolizing enzymes. In the elderly aged 75 and over, regardless of whether the medicine is received in the hospital or by pharmacy preparation, in about 70 percent of the patients, three or more types of pharmaceutical agents are prescribed. Thus, although the information about the drug metabolizing enzyme is provided to the medical staff, in order to properly utilize the information, it is necessary to check whether the information about the same drug metabolizing enzyme is described in the package insert of the other pharmaceuticals that the patient is concurrently receiving. A means by which to quickly and easily retrieve the information about the drug metabolizing enzyme printed in the package is necessary and such a tool will be developed in the near future.