Warfarin, an oral anticoagulant originally derived from a plant, is one of the most widely used in oral anticoagulation to reduce the risk of thromboembolic events. It is an affordable medicament, however its drug therapy is complex because it has a narrow therapeutic index and it does not follow standard dose response. The effectiveness of warfarin, is strongly affected by patient characteristics such as age, presence of comorbidities, and the concomitant use of another drug. Warfarin has the potential to interact with many drugs, herbs, and food, which increases the risk of adverse events. The mechanisms of interaction between drugs and herbs are varied because of their complex metabolism. Potential interactions between herbal products and drugs are a safety concern for drugs with a narrow therapeutic index or for patients receiving drug treatment for chronic diseases; both of these apply to warfarin pharmacotherapy.