An event in which foods and drugs consumed at about the same time alter the ability of the body to use one or the other; a side effect caused by the interplay of foods and drugs. Certain foods are known to interact with specific drugs in undesirable ways. For example, grapefruit juice and some drugs used to treat high blood pressure do not mix well; consuming calcium channel blockers and grapefruit juice may lead to headaches and light-headedness. A pharmacist should be consulted about any questions, and notes attached to a prescription drug will mention any known adverse interaction with food.