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Get a Handle on Herb-Drug Combinations

What’s safe, what’s not? We help you sort out your medicine chest.
By Michael Castleman
November/December 2005
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Lately, some scary headlines have warned that simultaneous use of medicinal herbs and common drugs can be dangerous. Well, yes and no. Herb users should certainly understand the potential risks of botanical medicines and take care to avoid some herbs before surgery and while taking certain pharmaceuticals. But despite the nerve-rattling headlines, the problem of herb-drug interactions is a minor issue compared with the problems caused by prescription drug side effects.

In 2004, a team of research pharmacists at the University of Pittsburgh surveyed 458 Veterans Administration (VA) hospital patients in Pittsburgh and Los Angeles about their use of drugs and supplements (vitamins and herbs). Almost half of the respondents said they took supplements while also taking prescription medications. Most VA patients are older men. Their most common herbs included garlic (Allium sativum), ginkgo (Ginkgo biloba), Asian ginseng (Panax ginseng) and saw palmetto (Serenoa repens), the best herb for preventing and treating prostate enlargement. The researchers noted that about half of those mixing drugs and supplements faced potentially risky interactions. However, of the herb-supplement interactions they analyzed, a whopping 94 percent were not found to be serious.

Contrast this with what University of Toronto researchers discovered in a 1998 review of serious drug side effects among U.S. hospital patients spanning 30 years (1966 to 1996). This study did not look at drug overdoses or prescribing errors but serious side effects from drugs taken as prescribed. The researchers estimated that more than 2 million hospital patients a year suffered serious drug side effects; these side effects killed 106,000 patients annually, making drug side effects the nation’s fifth leading cause of death.

These two studies clearly show that from a public health perspective, pharmaceuticals are the problem, not herbs or herb-drug interactions. That said, however, herbs should be used carefully and safely — and herb users should understand interactions that might cause problems.

The Main Problem: Anticoagulant Herbs Before Surgery

The woman had breast cancer, and surgeons at the University of Colorado Health Sciences Center in Denver performed a mastectomy that should have been routine. But shortly after she was sewn up, this woman hemorrhaged and required additional surgery — traumatic and expensive — to close the bleeding blood vessels in her chest. Why did she bleed so unexpectedly and so profusely? Prior to surgery, she’d taken ginkgo, ginseng and dong quai (Angelica sinensis) — without knowing that all three herbs impair blood clotting, and without telling her doctors.

At M.D Anderson Cancer Center in Houston, a man had surgery to remove a brain tumor. Afterward, he bled profusely and required two additional surgeries to stop the bleeding. The surgical team could not figure out why the man bled. Then, during a follow-up appointment, the patient’s wife casually mentioned that her husband drank a lot of ginseng tea, which is anticoagulant. All of the trauma, time and expense of those additional surgeries could have been avoided if someone had asked him about his herb use — and told him to stop using ginseng two weeks before surgery.

These cases, both culled from recent medical journals, are unusually serious. But they point to a real problem. Many people take herbs shortly before surgery. A recent survey at Texas Tech University in Lubbock showed that 43 percent of people awaiting surgery took garlic supplements and 32 percent used ginkgo — both are anticoagulants that might contribute to excessive bleeding. A University of Colorado Health Sciences Center survey showed that 27 percent of people scheduled for surgery consumed herbs that might trigger bleeding.

“Better safe than sorry,” says Jessica A. Alexander, M.D., a professor of anesthesiology at the University of Texas Health Sciences Center in San Antonio. “Stop taking anticoagulant herbs at least two weeks before scheduled surgery.”

If you or a loved one require unscheduled surgery, make sure to inform the hospital staff about any herbs or supplements you are taking.

Among the current 20 bestselling herbs, those with anticoagulant action include garlic, ginkgo, ginseng, eleuthero (Eleutherococcus senticosus), evening primrose (Oenothera biennis) oil, grape seed extract and ginger (Zingiber officinale).

Other herbs that can impair blood clotting include andrographis (Andrographis paniculata), bilberry (Vaccinium myrtillus), celery, dong quai (also known as Chinese angelica), feverfew (Tanacetum parthenium), green tea (Camellia sinensis), horse chestnut (Aesculus hippocastanum), kava (Piper methysticum), pau d’arco (Tabebuia spp.) and turmeric (Curcuma longa).

There’s another less serious risk from mixing anticoagulant herbs, vitamins and drugs — bruising. Everyday mishaps — bumping into things, for instance — can rupture the tiny capillaries in the skin. But clotting typically happens quickly so bruises usually don’t appear. However, if you mix anticoagulants — any combination of the herbs just mentioned with aspirin or such medications as warfarin (Coumadin) — minor bleeds take longer to clot, and noticeable amounts of blood might pool under your skin. That’s a bruise. If you notice you’re bruising unusually easily, assess the drugs and herbs you take, and consider cutting back. When in doubt, be sure to check with your physician or pharmacist — or with an alternative medicine practitioner, who may well know more than mainstream health professionals about herb- drug interactions.

St. John’s Wort and the Hazards of “Doubling Up”

St. John’s wort (Hypericum perforatum) is the best herbal option for depression. Many studies have shown that it’s as effective as several popular pharmaceuticals, among them, Prozac, Paxil and Zoloft.

The problem is that illness, especially depression, can cloud judgment. Antidepressant medications, both St. John’s wort and pharmaceuticals, often take several weeks to start elevating mood. For people suffering depression, those weeks can drag on and on — and people in the throes of depression might be tempted to supplement one of the drugs with the herb, or vice versa. This is a potentially fatal mistake.

Both St. John’s wort and the Prozac family of antidepressants, the SSRIs (selective serotonin reuptake inhibitors), affect the body’s levels of a compound called serotonin. Combining the herb and any SSRI can boost serotonin to toxic levels, a condition known as “serotonin syndrome.” Symptoms include intoxication, euphoria, drowsiness, clumsiness, loss of consciousness and possibly death. Serotonin syndrome also is possible if you mix St. John’s wort and certain migraine drugs, such as Imitrex, Zomig, Maxalt and Amerge.

The risk of serotonin syndrome from combining St. John’s wort and antidepressants is a particularly hazardous example of the dangers of “doubling up,” simultaneously taking an herb and drug that have the same effects on the body. Don’t double up. If you take aspirin for pain, inflammation or fever, don’t take white willow bark (Salix spp.), which is essentially herbal aspirin. That’s like taking an overdose of the drug. If you take valerian (Valeriana officinalis) as a sleep aid, don’t take pharmaceutical sleeping pills. If you take anxiety medication, be careful with herbal tranquilizers: chamomile (Matricaria recutita), passionflower (Passiflora incarnata) and hops (Humulus lupulus).

A large number of medications are prescribed to treat diabetes, a condition that affects millions of Americans. Diabetes involves abnormally high levels of sugar (glucose) in the blood. Diabetes medications reduce blood glucose levels — they’re “hypoglycemic.” Many herbs are also hypoglycemic. In general, hypoglycemic herbs are beneficial, because it’s best to prevent abnormal elevation of blood glucose. But if diabetics whose condition is controlled by medication also take hypoglycemic herbs, this is a form of doubling up that might reduce blood sugar to levels below what’s desirable. Herbs with hypoglycemic action include ginkgo, ginseng, eleuthero, horse chestnut and yohimbe (Pausinystalia johimbe). If you’re diabetic, you don’t have to stop taking these herbs. But your dosages of insulin and other diabetes medications might have to be reduced. If you’re a diabetic herb user, test your blood glucose frequently, and discuss the potential interactions of diabetes medications and hypoglycemic herbs with your primary-care physician or endocrinologist.

Don’t Take “Opposites”

If you take any medication for a chronic condition, don’t take herbs that have the opposite effect. For example, if you take anxiety medication, don’t take large doses of herbs or other products containing caffeine that can increase anxiety, among them coffee, tea and cola soft drinks. Ginseng and ephedra (Ephedra sinica, also known as ma huang) also have stimulant action.

Echinacea (Echinacea spp.), astragalus (Astragalus membranaceus), garlic and ginseng help stimulate the immune system and generally are celebrated as aids to the treatment of all manner of illness. But those who have had organ transplants must take anti-rejection medication, which is immune-suppressing. Immune-boosting herbs can negate this effect and raise the risk of organ rejection. Anyone taking medication for autoimmune conditions, such as lupus, also should avoid immune-boosting herbs because immune stimulation may aggravate those diseases.

Herbs and Birth Control Pills

St. John’s wort may interfere with the action of birth control pills. If you take it, consider using another contraceptive method. Some research also suggests that large doses of garlic may interfere with the Pill.

Meanwhile, birth control pills slow clearance of caffeine from the body. If you take the Pill, expect an extra buzz from coffee, tea and colas.

Herbs, Drugs and the Cytochrome P450 System: A Complicated Issue

Finally, a great many drugs and herbs affect the body’s cytochrome P450 system. This system, little known outside of professional medicine, involves a group of enzymes that participate in the metabolism of many drugs — and some medicinal herbs. When drugs and herbs that both affect the cytochrome P450 enzyme system are taken simultaneously, potentially problematic interactions are possible.

Space does not permit us to list all cytochrome P450 herb-drug interactions. However, here is list of popular herbs that affect this enzyme system and some of the drugs with which they may interact. If you take any of these herb-drug combinations, discuss potential interactions with your physician, pharmacist or alternative medical practitioner.

• Garlic can interfere with the effectiveness of some allergy medications (Allegra), some antifungal drugs (Nizoral), some pain medications (Sublimaze, Alfenta), calcium channel blocker blood pressure medications (Cardizem) and some cancer chemotherapy drugs (Taxol).

• Ginkgo can interact with Tylenol, Valium, some antidepressants (Prozac, Desyrel), estrogen, some asthma medications (theophylline), some antifungal drugs (Nizoral, Sporanox), some blood pressure medications (Inderal, Lopressor), some cholesterol-lowering drugs (Mevacor) and some narcotic pain relievers (Demerol, Ultram).

• Asian ginseng can interfere with the action of antidepressants (Prozac, Desyrel), narcotics (codeine, Demerol, Sublimaze, Ultram) and some blood pressure medications (Lopressor).

• St. John’s wort also can interfere with the effectiveness of some antidepressants (Prozac), some allergy medications (Allegra), some antifungal drugs (Nizoral), some pain medications (Sublimaze, Alfenta) and some cancer chemotherapy drugs (Taxol).

• Valerian might increase blood levels of many medications, among them the antihistamine Allegra, the antifungal Nizoral (ketoconazole), the cholesterol-lowering drug Mevacor and the cancer chemotherapy drug Taxol. If you take valerian with any of these drugs, your dose might have to be reduced.

The Bottom Line

Now back to those scary headlines. Herb-drug interactions can, indeed, be harmful. But these interactions are nowhere near as hazardous as pharmaceutical drug side effects. Observe these simple precepts and you shouldn’t have problems: Stop taking anticoagulant herbs two weeks before surgery. Don’t supplement drugs with herbs that have the same effect. Don’t mix herbs and drugs that have opposite effects. If you take the Pill, don’t take St. John’s wort or doses of garlic larger than what you’d use in food. And if you use garlic, ginkgo, ginseng, St. John’s wort or valerian, check with your physician or pharmacist to make sure you’re not taking any drugs linked to the cytochrome P450 enzyme system.


San Francisco-based health writer Michael Castleman, a frequent contributor to Herbs for Health, is the author of The New Healing Herbs (Rodale, 2001).

The reference list for this article is extensive. If you would like a copy, please send a self-addressed, stamped envelope to “Herb-Drug Interactions,” Herbs for Health, 1503 SW 42nd St., Topeka, KS 66609; or e-mail us at editor@Herbs ForHealth.com.


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