How to Avoid Bad Herb and Drug Interactions

Mixing the two can be a dangerous combination

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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 that combination for months. But his doctor wouldn’t talk about herbs, and his insurance plan didn’t allow for switching doctors or seeing alternative health care providers. Benton (not his real name) felt he needed both the herb, which gave him a much-needed energy boost, and the prescription medication, a blood thinner called warfarin. Afraid to continue and afraid to stop, he didn't know which way to turn.

Benton’s dilemma illustrates a potentially problematic side of herbal remedies: Combining herbs with pharmaceuticals may result in bad interactions. But finding information is difficult, and medical doctors are often hesitant to offer advice. Part of the problem is that Western science is just beginning to produce the research that doctors rely on to make such health care decisions.

“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. Yet herb-drug combinations offer many benefits—provided they are prescribed and used carefully.

Health care practitioners prescribe herb-drug combinations 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 inflames the liver.

“As the doctors kept increasing his Lasix, he became more frightened, and they became more pessimistic in their prognosis,” she says. Along with exercise, stress management, and changes in diet, McQuade Crawford recommended that her client augment his drug regimen with potassium-rich dandelion leaf and silymarin, the active compounds in milk thistle. In three months, he no longer needed the prescription diuretic, and medical tests showed his condition had improved.

Donald Brown, a naturopathic doctor and author of Herbal Prescriptions for Better Health (Prima, 1996), prescribes herbs to buffer side effects of strong medical treatments. He has, for example, advised chemotherapy patients to use 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 in switching from drugs to herbal care. “I like removing women from estrogen replacement therapy (ERT) of a chemical nature—I would much rather they take botanicals,” says Steve Morris, a naturopathic doctor in Mukilteo, Washington. He guides them through a careful six-month transition, slowly shifting the balance from drugs to herbs such as vitex and black cohosh. A faster change, he says, might bring on hot flashes, vaginal dryness, and irritability.

Practitioners are cautious because herbs are not used in traditional ways anymore. “We're standardizing them and concentrating them to make them stronger, [and] the effects may be stronger,” says Mary Hardy, a medical doctor practicing in California.

Although previously unseen reactions are rare, they can happen. Of particular concern are medications that affect the blood's ability to clot and those that affect the central nervous system. McQuade Crawford also urges special caution with certain other drugs: cardiac glycosides—compounds found in 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.

Dealing with the potential danger of herb-drug interactions above all requires open communication. Patients and health care providers also need to scrutinize information before panicking. McQuade Crawford cites North America’s “tremendous, fearful bias” against natural compounds; both medical journals and mainstream publications tend to focus on single harmful incidents.

Larry Benton’s fears, for example, aren’t unfounded, but may be based on faulty information. The account of an adverse reaction between warfarin and Asian ginseng turned out to be poorly reported, McQuade Crawford says; other research shows that ginseng compounds have the opposite effect. She cautions people to read widely, keep up with research, and work with health care providers to stay informed and monitor changes.

You can take a few steps on your own. If you’ve added something new to your regimen, look for changes: Herbal remedies often send gentle signals that all isn’t well.

“The great thing about herbs is that minor gastrointestinal upset is usually first. Many herbs have a built-in safety net,” says Brown, noting that herbal side effects tend to be milder than those caused by pharmaceuticals. Strong herbs such as ephedra, however, need to be treated with more respect. And working with your doctor is critical. Everyone holds a piece of the puzzle: Doctors know drugs and their actions, and patients need to know what they’re taking and why.

“There are a lot of ways that the drugs you take can affect your herbs,” says Hardy. “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.”

Hardy conducts seminars to teach medical professionals about herbal remedies, something they weren’t taught in medical school but want to learn. “Pharmacy schools used to have a course called pharmacognosy, which is about how plants are made into drugs, but it’s not really herbalism,” she says. Large pharmaceutical companies are beginning to take an 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.”

Reprinted with permission from Herbs for Health (Nov.-Dec. 1998). Subscriptions: $24/yr. (6 issues) from Box 7708, Red Oak, IA 51591-0708. Copyright 1998, Herbs for Health.

To Mix or Not to Mix
Here are a few examples of possible herb-drug interactions. If you’re concerned about any combinations, contact your health care practitioner.
Source: Herbs for Health (Nov.-Dec. 1998).

Bromelain
(from pineapple)
Increases bleeding risk when taken with anticoagulants

Cola nut
May strengthen effects of brain stimulants (psychoaneleptic drugs) and caffeinated beverages

Echinacea
Might counteract immune-suppressant drugs

Ephedra, Ginseng
May increase side effects of stimulants

Garlic, Ginkgo
May enhance anticoagulant and antiplatelet drugs

Ginger
Reduces nausea from chemotherapy

Grapefruit juice
Dangerous combined with blood-pressure medicine (calcium channel blockers)

Hawthorn
May enhance action of cardiac glycosides and ease their side effects

High-berberine herbs
(goldenseal, Oregon grape, barberry)
Counteract short-acting anticoagulants

High-fiber herbs
(fennel seed, psyllium husk, marshmallow root, Icelandic moss, apple pectin, flaxseed, aloe gel, slippery elm)
May delay absorption of medications taken at the same time

High-tannin herbs
(tea, white oak bark, bearberry, witch hazel, black walnut husk, raspberry leaves)
Reduce absorbability of drugs

Licorice
May worsen effect of drugs that cause potassium loss; lengthens effectiveness time of corticosteroids

Siberian ginseng
Enhances antibiotics

Stimulant laxatives
(senna leaf and fruit, cascara sagrada bark, aloe vera leaf [not gel], buckthorn bark and berry, rhubarb root, castor oil)
Speed digestion, which reduces absorption time for drugs; chronic use results in loss of potassium, thereby strengthening side effects of cardiac glycosides and antiarrhythmic agents; simultaneous use of thiazide diuretics, corticosteroids, or licorice root increases potassium loss

St. John’s wort
May enhance effects of narcotics and selective serotonin reuptake inhibitors (SSRIs)

Valerian
Enhances sedatives, hypnotic drugs

—Mary Hardy, M.D.