Dangers of Herb-Drug Interactions

When people take herbs in addition to their pharmaceuticals, previously unseen reactions can happen.


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Larry Benton was scared. He had read that Asian ginseng might counteract a prescription drug that helps prevent blood clots, and he had been taking precisely that combination for months. But his doctor wouldn’t talk to him about herbs, and his insurance plan didn’t allow for switching doctors or seeing alternative health-care providers. Benton (not his real name) had difficulty finding information beyond the one report he’d seen, yet he said he needed both the herb, which he felt gave him a much-needed energy boost, and the prescription medication, a blood-thinner called warfarin. Afraid to continue taking the combination and afraid to stop, Benton didn’t know which way to turn.

The Good, the Bad and the Unknown

Benton’s dilemma illustrates a potentially problematic side of herbal remedies: When combining herbs with pharmaceuticals, bad interactions may result. But finding information on the subject is difficult, and medical doctors are often hesitant to offer advice. Part of the problem, some say, is that Western medical doctors are just getting acquainted with herbs. And Western science is just beginning to produce the research reports that doctors rely on to make decisions about their patients’ health care.

“Consumers are not well served by our medical climate,” says Amanda McQuade Crawford, a medical herbalist, president of the National College of Phytotherapy in Albuquerque, and founding member of the American Herbalists Guild.

But McQuade Crawford and others say that herb-drug combinations offer many health benefits—provided they are used and/or prescribed carefully.

Among those who believe that herbs and drugs can be effective partners is Mary Hardy, a medical doctor practicing in California and an Herbs for Health editorial adviser. However, whether it’s smart to prescribe an herb-drug combination depends on the needs of the individual patient, she says.

“It’s about balance,” Hardy says, “and about knowing what goal you’re trying to achieve and putting it in context of that goal.”

Why Combine?

Health-care practitioners who prescribe herb-drug combinations say they do so for many reasons, including using herbs to ease side effects from harsh, though potentially life-saving pharmaceuticals. They also use herbs to strengthen the effects of pharmaceuticals (allowing for a lower dose) and help patients withdraw from addictive or potentially harmful drugs. McQuade Crawford, for example, once helped a client who was taking antiviral drugs and a strong diuretic called Lasix to treat hepatitis C, a viral disease that causes the liver to inflame.

“As the doctors kept increasing his Lasix, he became more frightened and they became more pessimistic in their prognosis,” she says. Along with changes in diet, exercise and stress management, McQuade Crawford recommended that her client add potassium-rich dandelion leaf and silymarin, the active compounds in milk thistle, to his regimen, all in addition to the Lasix and antivirals. In three months, he no longer needed the prescription diuretic, she says, and his doctors’ tests showed improvement in his liver enzymes and viral load.

Donald Brown, a naturopathic doctor and author of Herbal Prescriptions for Better Health (Prima, 1996), says he prescribes herbs to buffer the side effects of strong medical treatments. He has, for example, advised chemotherapy patients to use herbs such as astragalus and Siberian ginseng to help their bone marrow produce white blood cells more efficiently.

But, he adds, “I err on the side of safety...I’m not an advocate of using St. John’s Wort [an herbal antidepressant] with prescription antidepressants or kava [a relaxant] with anti-anxiety medications because we really don’t know what the mechanism of action is for those herbs. We’re getting an idea, but we don’t know yet.”

Others add that careful coordination and supervision are important, especially when switching from drugs to herbal care, such as women who want off of pharmaceutical estrogen replacement therapy (ERT).

“I like removing women from ERT of a chemical nature—I would much rather they take botanicals,” says Steve Morris, a naturopathic doctor in Mukilteo, Washington.

Nonetheless, Morris guides them through a careful transition, taking six months to leave ERT for botanicals such as vitex and black cohosh, slowly shifting the balance from drugs to herbs. If done more quickly, he says, patients may experience hot flashes, vaginal dryness, and irritability.

Cause for Caution

Why are practitioners so cautious? Aren’t herbs safe?

“We’re not using herbs in the traditional way anymore,” Hardy says. “We’re standardizing them and concentrating them to make them stronger, [and] the effects may be stronger.”

When patients take one or more of these modern herbs in addition to their prescription pharmaceuticals, she says, previously unseen reactions can happen, although they’re rare. Of particular concern are herbal and pharmaceutical medications that affect the blood’s ability to clot and those that affect the central nervous system, Hardy and others say.

To this cautionary list, McQuade Crawford adds cardiac glycosides—compounds found in some plants that act on the heart muscle—and synthetic diuretics, especially when both are combined with licorice, which can increase edema and even lead to arrhythmia.

What to Do

Dealing with the potential danger of herb-drug interactions requires, above all, open communication, McQuade Crawford says—even if your medical doctor isn’t open to herbal remedies.

“I have never had one single herb-drug interaction in thirteen years of ­practice,” she says, “and I’ve seen many patients who continue under their physician’s primary care. This isn’t because I’m so clever—this is because the herbs are safe when we understand [how they function] and work within ethical guidelines and monitor our patients or clients so that we can catch problems before they develop.”

Additionally, patients and their health-care providers need to scrutinize information before panicking, she says. In North America, there’s a “tremendous, fearful bias” against natural compounds, McQuade Crawford says, and both medical journals and mainstream publications tend to focus on single incidents of harmful herb-drug interactions. Larry Benton’s fears, for example, aren’t unfounded, but they may be based on what is turning out to be faulty information. On examination, the report of an adverse reaction between warfarin and Asian ginseng turned out to be poorly reported, McQuade Crawford says, because other research shows that ginseng compounds have exactly the opposite effect, although this is still being researched.

The point, she says, is that people need to read widely and keep up with the research as best they can. Then they should work with their health-care provider step by step, both to keep informed and to monitor their health. McQuade Crawford adds that in Europe, where adverse drug reporting is better established, members of both the government and medical community understand that interactions are unusual, and something to watch out for rather than fear.

Individual Action

To make sure that an herb-drug combination is safe, you can take a few steps on your own, experts say. For example, if you’ve added something new to your regimen, look for a change, Hardy says. If you had been fine, then experienced some discomfort, whatever you did differently may be causing the problem. Brown adds that herbal remedies often send out gentle signals that all isn’t well.

“The great thing about herbs is that minor gastrointestinal upset is usually first,” he says. “Many herbs have a built-in safety net; the symptoms are more mild in nature.” Strong herbs such as ephedra, however, need to be treated with more respect, he says (for more about herbs and their possible effects when combined with pharmaceuticals, see the chart on page 41).

Working with your doctor, especially if you use a lot of medication, is critical, Hardy says.

“The more medication you take and the stronger medication you take,” she says, “the more you need your doctor to be your partner” because the doctor and the patient each hold a piece of the puzzle: The doctor knows drugs and their ­actions, and patients know what they’re taking and why.

“There are a lot of ways that the drugs you take can affect your herbs,” she continues. “You can’t really think about them all. The bottom line is partnering with your physician. If he or she won’t [work with you], find a pharmacist or a nurse who will . . . you need that medical advice.”

Keep in mind, too, that the popularity of herbs has introduced a new, often unfamiliar element into the arena of conventional health care—one with which many medical doctors struggle.

“There’s very little education [about herb-drug interactions] in medical schools,” says Hardy, who conducts seminars at hospitals and medical schools to teach medical professionals how to give advice about herbal remedies. “Pharmacy schools used to have a course called pharmacognosy, which is about how plants are made into drugs, but it’s not really herbalism.”

However, she says, more and more physicians want to learn. Brown adds that large pharmaceutical companies are beginning to take interest in herbal remedies, so health-care professionals’ awareness will increase as these companies launch educational campaigns. For now, McQuade Crawford says, the best approach may be to encourage your doctor to forge a partnership with an herbalist, naturopath, or other alternative health-care provider.

“How can busy doctors be expected to stop what they’re doing and learn herbs for two years?” she asks. “The important thing is to work in concert for the best interest of the patient.”

Erika Lenz is assistant editor of Herbs for Health. 

Additional reading

American Herbal Products Association. Botanical Safety Handbook. Edited by Michael McGuffin, Christopher Hobbs, Roy Upton, and Alicia Goldberg. New York: CRC Press, 1997. 

Brinker, Francis. Herb Contraindications & Drug Interactions. Sandy, Oreg.: The Eclectic Institute, 1997. 

Newall, Carol, Linda Anderson, and J. David Phillipson. Herbal Medicines: A Guide for Health-Care Professionals. London: The Pharmaceutical Press, 1996. 

The Complete German Commission E Monographs—Therapeutic Guide to Herbal Medicines. Edited by Mark Blumenthal, Werner R. Bussey, Alicia Goldberg, Jorg Greenwald, Tara Hall, Chance W. Riggins, and Robert S. Rister (S. Klein, trans.). Austin, Texas: American Botanical Council, 1998.