It is the process in which a drug affects the activity of a drug when both are administered together. This process can either increase the drugs effect or my decrease the drug activity. In other words it is the action of one drug upon the effectiveness or toxicity of another. Drug interaction is the interaction shown by a substance which affects the activity of the administered drug. The substance which is affecting a drug activity can be another drug when both are administered together. This can also be studied as drug-drug interaction. This interaction can be synergistic or antagonistic in nature thereby causing either an increased or decreased drugs effect. Also there may be a condition in which new a new effect can be produced that is neither produced on its own. However, the interactions may also exist between drug and food called drug-food interactions. There are cases where a particular food should not be taken when a particular drug is under administration as it may result in severe crisis within the system. These accidents usually occur as a result of misuse or due to lack of knowledge about the active ingredients involved in its composition. The study of these interactions therefore seems to be important from the point of practice of medicine.