It is important for the oncologist to appreciate that patients they are treating may be using dietary supplements during their conventional cancer treatment. As patients are often reluctant to divulge this information, it is helpful for the oncologist to take the initiative and ask. Patients use a different hierarchy of evidence to inform their decision making regarding which supplements to utilize, most frequently relying on advice of others who claim to have benefitted from the intervention or the internet. Especially for the patient undergoing active treatment with radiation or chemotherapy, the oncologist needs to know which supplements are being used. Although the patient may assume that the vitamin or botanical supplement is natural and hence safe, potential supplement:drug interactions may occur. The cytochrome p450 isoform 3A4 is involved in the metabolism of many chemotherapy drugs. Botanicals may induce or inhibit the isoform potentially leading to a significant alteration in the concentration, effectiveness and/or toxicity of the cancer drug. Most of these potential interactions are more theoretical than clinically relevant. Similarly, an oxidant:antioxidant interaction is also possible between supplements with significant antioxidant activity in patients receiving radiation or chemotherapy that works by way of generation of oxidative damage to tumor DNA. Again, although greatly feared, such detrimental interactions have not been well-documented other than a single study of vitamin E in head and neck cancer patients undergoing radiation. This session will discuss the rational use of dietary supplements that may be safe and beneficial for cancer patients undergoing active treatment.