Herb-Drug Interactions

What herb-drug combinations should I avoid?

Herbal supplements are popular these days, but very few people have given up on mainstream medicine. Most of us still pop aspirin, see our physicians regularly, and pick up prescriptions from the pharmacy. Mixing herbs with traditional medicines can be the best of two worlds — as long as you mix wisely.

Many popular natural remedies can clash with prescription and non-prescription drugs, sometimes with severe consequences. Dangerous interactions between herbs and medications appear to be on the rise, largely because doctors are in the dark about their patients’ use of supplements. Of the roughly 100 million Americans who use herbal remedies every year, only 18 million mention it to their doctors. For your own protection, be sure to tell your doctor about any herbal supplements you’re taking, especially before you start a new prescription. And take a close look at the list below. You may find that your favorite supplement doesn’t get along with its neighbor in your medicine chest.

Those who take prescription drugs for migraines may want to be especially careful about taking certain herbs at the same time. Researchers at the University of Utah Health Sciences Center reported that ginkgo biloba, ginseng, echinacea, St. John’s wort, and large quantities of garlic could interact toxically with triptans and other migraine medications, as well as with tricyclic antidepressants, also used to treat migraines.

According to a report in the Archives of Internal Medicine, these common herbs can all interact with medications:

Feverfew. This herb can help to prevent the pain and nausea of migraine headaches when taken daily, but it also thins the blood. Specifically, feverfew interferes with the action of platelets, the cells that clump together to form blood clots. If combined with warfarin or other blood thinners (warfarin is generally used to reduce the risk of blood clots and heart attack), feverfew could potentially lead to severe bleeding. So, do not use feverfew if you have a condition of active bleeding, such as an ulcer. Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen may increase any risk of bleeding, and they may also block feverfew’s actions against migraines.

Ginkgo biloba. Like feverfew, this popular memory booster can thin the blood by keeping platelets from sticking together. Therefore, it shouldn’t be mixed with warfarin, regular doses of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDS), or other blood thinners: According to Pharmacist’s Letter, such a combination could trigger a bleeding stroke in certain people. There’s also some possibility that the herb hampers the effectiveness of anti-seizure medications such as carbamazepine, phenytoin, or phenobarbital. Ginkgo may also alter the effects of insulin and therefore should not be used in someone suffering from diabetes.

According to the Natural Medicines Comprehensive Database, ginkgo can increase blood pressure if used in combination with thiazide diuretics (drugs generally prescribed for treatment of edema due to congestive heart failure, kidney problems, cirrhosis of the liver, or other conditions in which you need to eliminate excess water). It may also be risky if combined with antidpressants known as monoamine oxidase inhibitor (MAOIs). On the positive side, taking ginkgo extract with certain antidepressants, including the selective serotonin reuptake inhibitors (SSRIs) fluoxetine (Prozac) and sertraline (Zoloft) can reverse impotence and some other types of sexual problems caused by the SSRIs.

Saint-John’s-wort. This herb seems to ease mild to moderate depression, but scientists don’t know exactly how it works. Such uncertainly calls for caution, and several potentially harmful drug interactions have been cited, so be sure to consult with your doctor before taking this supplement. Saint-John’s-wort may mildly mimic MAOI drugs and should not be used when taking antidepressent medication such as phenelzine. On the other hand, its effect may duplicate that of SSRIs such as Prozac and Zoloft. If so, Saint-John’s-wort could cause headache, sweating, dizziness, and agitation when taken in combination with SSRIs. It can also interfere with certain seizure medications as well as lithium. Saint-John’s-wort may intensify the effects of sedatives and diabetes medications.

Research from the National Institutes of Health (NIH) has shown that the herb interacts with, and could limit the effectiveness of, some drugs used to treat HIV (such as indinavir) and cancer (such as irinotecan), as well as with drugs like cyclosporine used to help prevent the body from rejecting transplanted organs. Theoretically, Saint-John’s-wort may increase sun damage if taken at the same time with photosensitizing drugs such as tretinoin (Retin-A). Saint-John’s-wort can also interfere with many medications used to treat high cholesterol, high blood pressure, and other heart conditions such as angina. It may also decrease the effectiveness of oral contraceptives.

Licorice. Large quantities of pure licorice (not to be confused with the common red or black candy sticks) may ease stomach ulcers, inflammation of the upper respiratory tract, and other ailments, but licorice can also interfere with many medications. Like feverfew and ginkgo biloba, licorice can interfere with the action of platelets and should not be used with nonsteroidal anti-inflammatory drugs (NSAIDs), warfarin, or other blood thinners. The herb may offset the actions of immunosuppressive drugs, including corticosteroids (prescribed for a wide range of disorders, from asthma to cancer). Licorice may also reverse the effects of blood-pressure medications and worsen the adverse side effects of the heart medication digoxin. It should not be taken in combination with diuretics because it may cause potassium depletion.

Ginseng. This all-purpose herb, touted as a source of energy and stamina as well as a remedy for many diseases, may block the action of warfarin. In addition, ginseng has been known to cause headaches, tremors, and manic episodes in patients taking the MAOI phenelzine, which is used to treat depression . Theoretically, American ginseng (as opposed to Chinese ginseng) could interfere with antipsychotic drugs, hormone therapy, MAOIs, and stimulant drugs, according to Pharmacist’s Letter. To stay on the safe side, you should avoid mixing ginseng with heparin or aspirin, ibuprofen, or any other other type of NSAID. If you are an insulin-dependent diabetic, check with your doctor — ginseng could reduce the amount of insulin you need to take.

Ginger. A gram or so of powdered ginger can help ease nausea, but it can also interfere with platelet action. Of course, this means ginger shouldn’t be taken with aspirin, warfarin, or other blood thinners. Pharmacist’s Letter cautions that the spice, if taken in large quantities, could theoretically interfere with cardiac, diabetes, or blood pressure drug therapy.

Garlic. Often used to help rein in high blood pressure and high cholesterol, garlic or garlic pills taken in large doses also thins the blood. Not surprisingly, people taking warfarin, regular doses of aspirin, or other blood thinners should not use garlic for anything other than seasoning.

Researchers have also found that garlic can cause potentially harmful side effects when combined with the anti-HIV drug saquinavir, a protease inhibitor. According to the study in the journal Clinical Infectious Diseases, doctors and patients should be cautious about using garlic supplements during HIV therapy. Garlic may also cause hypoglycemia and should be used cautiously with diabetes medications.

Valerian. A proven sleep aid, valerian may trigger extreme drowsiness if mixed with barbiturates or medications for insomnia or anxiety; it’s also unwise to mix the herb with alcohol. According to the Pharmacist’s Letter, valerian may exacerbate drowsiness and other side effects of antihistamines (often prescribed for allergies), and should not be used in combination with tranquilizers, opioid analgesics, or other drugs that have sedative properties.

Kava. Kava is purported to have calming effects for people suffering from anxiety. The herb can amplify the effects of other sedatives, so should never be taken in combination with benzodiazepines, barbiturates, or any other sedative drugs. Kava can interfere with antipsychotic and Parkinson’s medications and should never be used in combination with them. It should also never be used with alcohol. Kava can cause thinning of the blood and should not be taken with blood thinning medications. Because kava has been associated with liver problems, the U.S. Food and Drug Administration cautions against using kava if you have a liver condition or are taking any drug that affects the liver.

This list is by no means comprehensive. Consult with your doctor or pharmacist first before taking herbal supplements. For more information on herb-drug interactions, you may want to contact the Pharmacist’s Letter, which publishes the Natural Medicines Comprehensive Database, providing reliable data on 1,000 herbs and nonherbal products, including common uses, safety, effectiveness, and interactions with drugs, foods, and other herbs and supplements. The database is available both in print and on the Web. For more information, please contact the Pharmacist’s Letter, Box 8190, Stockton, CA 95208 (phone 209/472-2240).


Sorting Out the Worst Offenders Among Herbal Supplements, Darves, Bonnie ACP Internist, October 2009

Garlic Supplements Can Impede HIV Medication, National Institutes of Health, December 5, 2001.

St. John’s Wort and the Treatment of Depression, National Center for Complementary and Alternative Medicine.

Herbs, Headache Meds, Could be Dangerous Combination, HealthDay, June 19, 2003.

FDA Consumer Advisory Kava-Containing Dietary Supplements May Be Associated With Severe Liver Injury March 25, 2002

Melanie Johns Cupp. Herbal Remedies: Adverse Effects and Drug Interactions. American Family Physician. March 1, 1999. American Academy of Family Physicians.

American Cancer Society. Understanding Dietary Supplements.

University of Texas-El Paso/Austin Cooperative Pharmacy Program. How Popular Is Herbal Medicine in the United States?

University of Michigan Health System. Selected Herb-Drug Interactions.

© HealthDay

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