September 2008
One-minute consult: Herbs that change drug effects
By Bill J. Gurley, Ph.D.
Bill J. Gurley, Ph.D., professor of pharmaceutical sciences, College of Pharmacy, University of Arkansas for Medical Sciences.
Q How significant is the risk of mixing drugs and herbs?
A It can be very significant. When we first started studying drug-herb interactions about 10 years ago, we learned of a couple of patients who rejected their kidney transplants. At the time they were taking St. John's wort along with their antirejection drug, cyclosporine. In our subsequent research, we found that St. John's wort was a potent inducer of certain enzymes in the liver and intestines that process many medications. So if more enzymes are produced, the medicine gets processed more quickly and less of it reaches the bloodstream. You may be taking a certain dose, but not enough is absorbed to produce the desired pharmacologic response. St. John's wort may render birth-control pills ineffective, as well as cholesterol-lowering drugs, certain chemotherapy drugs, blood-pressure drugs, anti-HIV medications, blood thinners, and many others.
Q Any other herbs to be wary of?
A Goldenseal is another one to be careful with. It's often packaged with echinacea to treat colds and gastrointestinal problems. Its effect is opposite that of St. John's wort. It inhibits the two most important drug-metabolizing enzymes, meaning that it may allow certain medications to reach unusually high concentrations—at times even toxic levels—in your bloodstream. It has the potential to affect about 75 percent of all medications, including antidepressants, antipsychotics, beta-blockers, and calcium channel blockers. I study Civil War medicine as a hobby. At a recent conference on the topic, a presenter mentioned that in those days goldenseal was often given with quinine to prolong its effects. Now I know why.
Q What's your advice to consumers?
A Many people don't tell their doctors they're taking supplements because they're afraid they're going to get chastised. But it's important for your doctor to know because of the potential for interactions. If you're taking medications long-term to treat things such as high cholesterol or high blood pressure, you should seriously consider avoiding botanical supplements completely. Though most are likely not going to be a problem, we've only scratched the surface in evaluating them.
This article first appeared in the September 2008 issue of Consumer Reports on Health.
A It can be very significant. When we first started studying drug-herb interactions about 10 years ago, we learned of a couple of patients who rejected their kidney transplants. At the time they were taking St. John's wort along with their antirejection drug, cyclosporine. In our subsequent research, we found that St. John's wort was a potent inducer of certain enzymes in the liver and intestines that process many medications. So if more enzymes are produced, the medicine gets processed more quickly and less of it reaches the bloodstream. You may be taking a certain dose, but not enough is absorbed to produce the desired pharmacologic response. St. John's wort may render birth-control pills ineffective, as well as cholesterol-lowering drugs, certain chemotherapy drugs, blood-pressure drugs, anti-HIV medications, blood thinners, and many others.
Q Any other herbs to be wary of?
A Goldenseal is another one to be careful with. It's often packaged with echinacea to treat colds and gastrointestinal problems. Its effect is opposite that of St. John's wort. It inhibits the two most important drug-metabolizing enzymes, meaning that it may allow certain medications to reach unusually high concentrations—at times even toxic levels—in your bloodstream. It has the potential to affect about 75 percent of all medications, including antidepressants, antipsychotics, beta-blockers, and calcium channel blockers. I study Civil War medicine as a hobby. At a recent conference on the topic, a presenter mentioned that in those days goldenseal was often given with quinine to prolong its effects. Now I know why.
Q What's your advice to consumers?
A Many people don't tell their doctors they're taking supplements because they're afraid they're going to get chastised. But it's important for your doctor to know because of the potential for interactions. If you're taking medications long-term to treat things such as high cholesterol or high blood pressure, you should seriously consider avoiding botanical supplements completely. Though most are likely not going to be a problem, we've only scratched the surface in evaluating them.
This article first appeared in the September 2008 issue of Consumer Reports on Health.
