Herbs: Toxicities and Drug Interactions

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Medical Author:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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Medical Editor:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Any conventional medication can have side effects. These side effects are described and reported after drug trials and research studies have been conducted. Side effects are further reported and evaluated after the marketing of the medication. Information about drug components, interactions, usage in pregnancy, nursing and childhood, and dosing limits are outlined and made available in standard references for doctors treating patients. Furthermore, the formulations of the drugs must satisfy strict quality control standards to ensure conformity. These medications regularly contain virtually uniform quantities and ratios of substances.

In contrast to conventional medications, unconventional treatments (such as herbs) have little or no actual scientific basis so doctors can guide their patients regarding proper usage or potential toxicity. There are no standardized references and most of the herbal formulations have not been analyzed, are not uniform, and have not been quality controlled. One batch can be very different from the next.

Moreover, even if a given herb has a known toxicity, the manufacturer may or may not warn consumers. Manufacturers are not required to alert consumers to known dangers.

The point is that these "supplements" are not sanctioned, regulated, or supervised by any agency.

Data is coming, although slowly. Dr. Lucinda Miller of Texas Tech University Health Sciences reviewed known herb-drug interactions. Her review was published for doctors in the medical journal Archives of Internal Medicine. The list that follows is derived from this article and includes summaries of various herbs with particular focus on potential herb-drug interactions.

Keep in mind that the information in the "Uses" section is for the most part unsupported by verification of scientific studies. It should be noted that simply because herbs are "natural" treatments, they are not necessarily free from side effects.

• Chamomile
• Echinacea
• St. John's Wort
• Garlic
• Feverfew
• Ginkgo Biloba
• Ginseng
• Ginger
• Saw Palmetto

Chamomile

Uses: Chamomile is often used in the form of a tea as a sedative.

Reactions: Allergic reactions can occur, particularly in persons allergic to ragweed. Reported reactions include abdominal cramps, tongue thickness, tightness in the throat, swelling of the lips, throat and eyes, itching all over the body, hives, and blockage of the breathing passages. Close monitoring is recommended for patients who are taking medications to prevent blood clotting (anticoagulants) such as warfarin (Coumadin).

Echinacea

Uses: Largely because white blood cells in the laboratory can be stimulated to eat particles, Echinacea has been touted to be able to boost the body's ability to fight off infection.

Reactions: The most common side effect is an unpleasant taste. Echinacea can cause liver toxicity. It should be avoided in combination with other medications that can affect the liver [such as ketaconazole (Nizoral, Extina, Xolegel, Kuric), leflunomide (Arava), methotrexate (Rheumatrex), isoniazid (INH, Nydrazid, Laniazid)].

St. John's Wort

Uses: St. John's Wort is popularly used as an herbal treatment for depression, anxiety, and sleep disorders. It is technically known as Hypericum perforatum. Chemically, it is composed of at least 10 different substances that may produce its effects. The ratios of these different substances varies from plant to plant (and manufacturer).