Polypharmacotherapy, both psychotropic and nonpsychotropic, is widespread in various situations including psychiatric hospitals and general hospitals. As the clinical practice of using more than one drug at a time increase, the clinician is faced with ever-increasing number of potential drug interactions. Although many interactions have little clinical significances, some may interfere with treatment or even be life-threatening. The objective of this review is evaluation for drug-drug interactions often encountered in psychiatric consultation. Drug interactions can be grouped into two principal subdivisions : pharmacokinetic and pharmacodynamic. These subgroups serve to focus attention on possible sites of interaction as a drug moves from the site of administration and absorption to its site of action. Pharmacokinetic processes are those that include transport to and from the receptor site and consist of absorption, distribution on body tissue, plasma protein binding, metabolism, and excretion. Pharmacodynamic interactions occur at biologically active sites. In psychiatric consultation, these two subdivisions of drug interactions between psychotropic drugs and other drugs are likely to happen. We gathered informations of the drugs used in physically ill patients who are consulted to psychiatric department in Korea University Hospital. And we reviewed the related literatures about the drug-drug interactions between psychotropic drugs and other drugs.