Drug interactions and herbal interactions have increasingly become a subject of concern when managing our patients. This presentation will review the science and concepts of drug interactions as they apply to herbal and drug therapy. It will review the concepts of enzyme inducers and inhibitors of the cytochrome P450 systems. The presentation will focus on herbal products and their use when treating individuals who are on anticoagulant therapy and a practical and clinical approach to monitoring patients who are concurrently on both herbal and allopathic medication.