Complementary alternative medicines (CAMs), including food supplements, are taken widely by patients, especially those with cancer. Others take CAMs hoping to improve fitness or prevent disease. Physicians (and patients) may not be aware of the potential side-effects and interactions of CAMs with conventional treatment. Likewise, their known physiological effects could interfere with radiopharmaceutical kinetics, producing abnormal treatment responses and diagnostic results. Nuclear medicine physicians are encouraged to question patients on their intake of CAMs when taking their history prior to radionuclide therapy or diagnosis. The potential effect of CAMs should be considered when unexpected therapeutic or diagnostic results are found.