Herbs: Toxicities and Drug Interactions

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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, while breastfeeding, for pediatric patients, 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.


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).


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 (izoral, Extina, Xolegel, Kuric), leflunomide (Arava), methotrexate (Rheumatrex, Trexall), 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).