Researchers from the Mayo Clinic in Minnesota and Arizona collaborated to review the risks of herbal:drug interactions.

The abstract is a bit skimpy on details, but the American Pharmaceutical Association has a nice summary, which will be summarized further here.

First, the details.

  • 16 herbal products are potential problems.

And, the results.

  • St John’s wort
    • Induces cytochrome P450 (CYP)3A4, an enzyme involved in the metabolism of more than 50% of all prescription medications, including many used to treat heart arrhythmias, high blood pressure, and high cholesterol.
  • Motherwort
    • Inhibits the ability of blood to clot and increases the risk of bleeding.
  • Ginseng
    • Potentially toxic to the kidneys
    • May lower or raise blood pressure
    • Interacts with the blood thinner, warfarin (Coumadin), which increases the risk of bleeding
  • Ginkgo biloba
    • Increases the risk of bleeding when used with antiplatelet, anticoagulant, or antithrombotic agents (blood thinners)
  • Garlic
    • Increases the risk of bleeding in patients using anticoagulant or antiplatelet drugs
  • Grapefruit juice and black cohosh
    • Inhibit CYP3A4, which increases blood levels of…
      • Calcium-channel blockers
      • Cyclosporine
      • Statins
      • Midazolam (Versed)
      • Estrogen (Premarin)
      • Terazosin (Hytrin)
  • Hawthorn
    • Enhances the activity of digoxin (Lanoxin), which could cause toxicity
    • Increases the risk of bleeding from thromboxane A2
  • Saw palmetto
    • Increases the antiplatelet effects of warfarin, which increases bleeding risk
  • Danshen
    • Increased antiplatelet effects and bleeding risk
  • Echinacea
    • Increases the risk of liver toxicity from…
      • Statins
      • Fibrates (Atromid, Tricor, Lopid)
      • Niacin (Nicobid)
      • Amiodarone (Cordarone)
      • Tetrandrine (an alkaloid extracted from a Chinese medicinal herb traditionally used o treat high blood pressure)
    • Interferes with calcium channel blockers and may cause liver and/or kidney toxicity
  • Aconite
    • Can cause cardiac arrhythmias, ranging from slow heart rate and low blood pressure to fatal ventricular arrhythmias
  • Yohimbine
    • Decreases the effect of blood pressure drugs, including diuretics
  • Gynura
    • Associated with liver toxicity
    • Decreased activity of angiotensin-converting enzyme
  • Licorice
    • Potentiates the effects of spironolactone (Aldactone) and digoxin
    • Also, a risk of ventricular arrhythmias, including torsades de pointes (sudden death)

The bottom line?

Many drugs used to treat cardiovascular disease have a narrow therapeutic range. In other words, small changes in dosing or drug metabolism can lead to significant side effects.

If you’re a healthcare professional, you need to ask.

If you’re a patient, you need to tell the doctor what you are taking — including herbals.

4/5/10 15:29 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.