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
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
“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
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
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
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
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
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
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
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
• 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.