Dangers of Herb-Drug Interactions

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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

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

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

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

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

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

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

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.

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