A drug interaction is a situation in which a substance affects the activity of a drug when both are administered together. This action can be synergistic or aggressive or a new effect can be produced. Consequences of drug interactions with food and beverages may include late, decreased, or better absorption of a drug. Food can affect the metabolism, excretion and bioavailability of certain medications. The pharmaceutical interactions that are of special interest to the medical trails are primarily those that have negative effects on an organism. Drug-drug interactions can occur whenever a patient takes two or more drugs. Some interactions are both anticipated and desired, as when we combine drugs to treat diseases. On the other hand there are some interactions are unintended and undesired. It is therefore easy to see the importance of these pharmacological interactions in the practice of medicine. These chemical reactions are also known as pharmacological incompatibilities. The reactions can also occur when two or more drugs are mixed outside the body of the organism for the purpose of combined administration. Usually the interactions are antagonistic and it almost always affects both drugs. There are four basic mechanisms through which drugs can interact: Direct Physical or Chemical Interactions,Pharmacokinetic Interactions,Pharmacodynamic Interactions,Combined Toxicity.