Speaker: Mark Blumenthal. Recent surveys suggest that about 30% of adults who employ herbal dietary supplements are also simultaneously taking nonprescription and/or prescription drugs. Since herbal teas and supplements obviously contain pharmacologically active compounds, it is reasonable that numerous health professionals have raised questions regarding the potential risks that may ensue if herbal supplements compromise the effects of various pharmaceutical drugs. This phenomenon is clearly seen with the popular herbal dietary supplement St. John's wort (SJW), which has demonstrated to increase the activity of various isozymes in the cytochrome P450 enzyme system. This and other interactions are discussed.