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Am Fam Physician. 2002;66(7):1318-1321

Over the past few years, the amount of herbal products consumed in the United States has increased substantially. Although a significant number of patients are using herbal remedies, few physicians understand the use and potential adverse effects of these products. The U.S. Food and Drug Administration does not monitor the safety of herbal remedies. Manufacturers are expected to ensure their safety. Unfortunately, most manufacturers cannot afford the cost of studies to prove the safety and potential interactions of herbal therapies. Valli and Giardina wrote a review article on the benefits, adverse effects, and drug interactions of herbal therapies that have cardiovascular effects.

Some herbal therapies may be beneficial. An example is danshen (Salvia miltiorrhiza), which is used in Chinese hospitals for treatment of angina, acute myocardial infarction, and ischemic or thrombotic disorders. Some studies have shown a small benefit from danshen in patients with these disease processes, but placebo-controlled trials are lacking. In addition, danshen dilates coronary arteries at low dosages but constricts noncoronary arteries at higher dosages.

Another commonly used herbal therapy is garlic. Studies have shown that garlic use can lower serum cholesterol levels from 5 to 15 percent, reduce plaque size, and cause a modest reduction in hypertension. Nevertheless, knowledge about the active compounds and the exact mechanisms of action are lacking.

Other cardiovascular benefits can potentially occur with ginkgo, ginseng, hawthorn, horse chestnut seed, and yohimbine therapy. The authors emphasize that the studies on the efficacy of these medications are usually small, and there are a limited number of placebo-controlled trials to support them. They also caution that many herbal therapies may have an adverse effect on the cardiovascular system (see accompanying table). One of the most common adverse effects is platelet dysfunction. The therapies that have been linked to platelet dysfunction include danshen, garlic, ginger, and kava. Therapy with these products could become a potential problem in patients who are taking antiplatelet medications or have a bleeding disorder. Before initiating anti-platelet therapy, information about the use of herbal remedies should be obtained.

Another potential source of problems with herbal therapy is drug interactions. This is particularly true with warfarin therapy. Dong quai and garlic may increase the International Normalized Ratio (INR) in patients who are taking stable warfarin dosages. One case report of ginseng therapy showed a decreased INR in a patient who was taking a stable dosage of warfarin, but there is no other supporting data.

HerbAdverse effectComments
BelladonnaTachycardiaHerbal source of atropine
DanshenPlatelet dysfunctionIn vitro evidence of platelet antagonism
Dong quaiIncreased bleeding tendencyPresence of natural coumarins and in vitro evidence of platelet antagonism
FeverfewPlatelet dysfunctionIn vitro evidence of platelet antagonism not supported in clinical trials
GarlicIncreased bleeding tendencyCase reports of hemorrhage. In vitro evidence of platelet dysfunction but conflicting platelet and fibrinolytic evidence from clinical trials
GingerPlatelet dysfunctionConflicting results in studies of platelet antagonism in human trials
HypertensionAnimal studies of specific purified ginger compounds demonstrate pressor effects
Ginkgo bilobaIncreased bleeding tendency, platelet dysfunctionCase reports of central nervous system hemorrhage. Pharmacologic evidence of platelet antagonism; however, active compounds not present in sufficient amounts in most extracts
GinsengHypertensionAn abuse syndrome involving hypertension is described in chronic users; however, evidence from clinical trials also supports hypotensive effects.
HelleboreHypotension, bradycardiaAccidental ingestion occurs when plant is mistaken for another, especially gentian
KavaPlatelet dysfunctionLimited in vitro evidence
LicoriceHypertension, pulmonary edema, cardiomyopathy (rarely)Occur as a result of decreased inactivation of cortisol, causing symptoms of mineralocorticoid excess
Ma huangStroke, myocardial infarction, arrhythmia, hypertensionNumerous case reports of serious adverse events in healthy young people
MyocarditisRare case report
OleanderArrhythmiaCardiac glycosides cause symptoms similar to digoxin toxicity. Responds to digoxin antibody treatment
YohimbineHypertension, arrhythmiaIncreases norepinephrine levels and central sympathetic outflow via alpha2 antagonism.

Another drug interaction with herbal remedies that should be monitored is the potential impact on digitalis. The use of St. John's wort reduces serum digoxin levels. Herbal laxatives such as buckthorn, cascara sagrada, and senna can cause potassium loss that can lead to digitalis toxicity. A number of herbs including oleander, adonis, black Indian hemp, black hellebore, lily-of-the-valley, squill, and strophanthus contain an active cardiac glycoside that can potentiate digoxin.

The authors conclude that the growing use of herbal remedies in the United States has surpassed the available information on their potential benefits, risks, and drug interactions. Physicians should become familiar with the evidence about these alternative therapies. This will allow patients who wish to use herbal therapies an opportunity to do so in a safer manner.

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