An interaction is a generally unwanted result of combining two or more chemicals within the body. Sometimes it involves the result of direct chemical interactions (such as when two chemicals combine to create a third and unplanned chemical) and sometimes it relates to the impact on the body caused by treatment with more than one drug at a time, such as two drugs affecting the same system, even though the drugs don’t themselves combine to create yet another drug. Drug interactions are very common and while many have only minor effects they can be quite dangerous, even lethal.
Drug interactions are usually characterised by one of two general effects. One involves the drugs enhancing their effects (that is potentiating or working together to have a stronger action). For example, drugs that are used to thin the blood and reduce the possibility that the blood will clot (anticoagulants) are commonly affected by this problem. Combined treatments will work together and the blood could become so thin that bleeding could occur and it would be difficult for the blood to form a clot to stop the bleeding. One example would be taking aspirin while being treated with heparin since both are known anticoagulants. There are also herbs that have an anticoagulant effect and these can interact with medical anticoagulants. These herbs include cayenne and ginger which are specific herbal anticoagulants. There are other herbs and vitamins that have an anticoagulant effect – these include ginkgo biloba, garlic and vitamin E. The other general effect of course is just the reverse. This involves the drugs working against each other causing them to be less effective.