A drug interaction can be defined as an interaction between a drug and other drugs that prevent the drug from performing as expected. These processes may include alterations in the pharmacokinetics of the drug, such as modulations in the absorption, distribution, metabolism, and elimination (ADME) of a drug. Alternatively, drug interactions may be the result of the pharmacodynamic characteristics of the drug: the concomitant medication of a receptor antagonist and an agonist for the same receptor. The following interaction may increase or decrease the effectiveness of the drugs or the adverse drug reactions of the drugs. The possibilities of drug interactions should increase as the number of drugs being taken increases in patients. Therefore, patients taking several drugs simultaneously are at the greatest risk for interactions. Drug interactions can contribute to the increasing cost of healthcare because of the costs of medical care that are required to treat problems caused by changes in effectiveness or adverse drug reactions. The drug utilization review (DUR) system has been defined as a structured, ongoing initiative that interprets patterns of drug usage in relation to predetermined criteria and attempts to prevent or minimize inappropriate prescribing. The primary objectives of DUR are to improve the quality of health care for healthcare members and to assist in containing health care costs. In order to achieve these goals, prescription claims must be reviewed both prospectively and retrospectively. The DUR system supplies information to prohibit co-dispensing of contraindicated drugs which increases the risk of drug interactions properly to all the healthcare professionals participating in the care of the patients. In this article, we suggest the importance of DUR in relation to the contraindication of co-medication drugs.