Researchers believe some of the most common herbal products might prolong the sedative effect of anesthesia, increase bleeding during surgery and cause fluctuations in blood pressure.

Patients should tell their surgeons about all herbal products they use, along with prescriptions and over-the-counter remedies, to avoid dangerous interactions, said Dr. Charles McLeskey, an anesthesiologist at Scott & White Memorial Hospital in Temple.

At a conference this week in Dallas of the American Society of Anesthesiologists, McLeskey presented results of a survey of 979 presurgical patients. Seventeen percent said they take one of more herbal products.

The most common herbs listed were gingko biloba, garlic, ginger and ginseng -- all of which may prevent blood clots from forming and lead to excess blood loss in surgery. Two other popular herbs -- St. John's wort, an antidepressant, and kava-kava, a relaxant -- may prolong the sedative effect of anesthesia, McLeskey said.

The ASA suggests that patients stop taking herbal products at least two weeks before elective surgery and keep their doctors informed.

A spokeswoman for the Council for Responsible Nutrition, which represents makers of dietary supplements, said patients should try to bring the bottles with them anytime they visit a doctor or hospital.

"Anytime they are taking a dietary supplement they should mention that to their doctor," Cathy Fomus said. "They can interact with food, with each other and other prescription drugs."