Understanding Herb-Drug Interactions

Author: Constance Grauds, RPh

Herbal remedies have drug-like activity. They are often considered to be ?weak drugs.? Because herbs contain pharmacologically active constituents, they can potentially interact with over-the-counter and prescription medications. Although the list of potential herb-drug interactions is extensive, the following tables focus on the most serious or documented interactions. For further reference, a list of publications that contain extensive herb-drug interaction information is provided.

St. John?s Wort and Medications
St. John?s wort continues to rank as one of the top five best-selling products in the herbal market today. Customers are self-treating their mild-to-moderate depression with this popular herb. The list of drug interactions with St. John?s wort is growing, as science learns more about its ability to induce the cytochrome P450 metabolic pathway. Table 1 lists major prescription drugs that are also metabolized via the cytochrome P450 metabolic pathway (other interactions are as noted).

Herbs and Warfarin
Since even minor bleeding-time changes may be life-threatening to certain patients, it is important to know which herbs may pose a potential risk, as well as which herbs have documented reports of changes in blood clotting. Table 2 provides a list of herbs that cause changes in blood clotting. Consult with patients who are taking any of these herbs while taking warfarin.

Herb-Drug Interaction References
The more popular herbal remedies have become in modern times, the more scientific research and case reports have come to light regarding potential and actual herb-drug interactions. The following references are well researched and serve as good resources for in-depth information about herb-drug interactions:

Safety comes first in product selection and drug treatment. Reports of herb-drug interactions are listed on the FDA?s MedWatch web site at www.fda.gov/medwatch. Report any documented herb-drug interactions to this program at 800-FDA-1088.

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