Anesthesiologists are conducting research to determine exactly how certain herbs and dietary supplements interact with certain anesthetics. They are finding that certain herbal medicines may prolong the effects of anesthesia. Others may increase the risks of bleeding or raise blood pressure. Some effects may be subtle and less critical, but for anesthesiologists anticipating a possible reaction is better than reacting to an unexpected condition. So it is very important to tell your doctor about everything you take before surgery.