Many Americans use dietary supplements, including herbal products, in the belief that they are natural and safe. Patients with cancer use them often to enhance the effects or to reduce the adverse reactions of cancer treatments. However, few herbs have been thoroughly studied in humans. Therefore, their interactions with prescription drugs and the clinical relevance, remain undetermined. These interactions could be pharmacokinetic in nature when an herb alters the absorption, metabolism, or excretion of other drugs, or pharmacodynamic in which it affects the mechanism of action of other drugs when consumed together. Following are a few relevant herb-drug interactions encountered in the oncology setting.