Interactions Between Drugs and Herbs

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In response to the increasing popularity of herbal remedies, medical journals have recently been publishing long lists of warnings about potential interactions between drugs and herbs. Although some of these interactions are indeed serious (such as those which have occurred between standardized preparations of St. John’s wort and several prescription medicines), many others are purely speculative.

One example of a speculative interaction is between herbal and prescription diuretics (agents that increase urination) used to treat edema (fluid accumulation) and hypertension. Given that diuretics continue to be some of the most frequently prescribed drugs in the United States, this warning could theoretically apply to millions of people. According to the experts, there are two possible interactions. First, the herbal diuretic can boost the effect of the drug, thus lowering blood pressure excessively. Second, the combination of the drug and the herb could lower blood potassium to dangerous levels.

Do herbs have diuretic actions?

The potentially dangerous herb most often cited in this context is dandelion (Taraxacum officinale), a curious choice to single out. In actuality, dandelion is one of the weakest herbal diuretics–there is even some debate about whether it is a diuretic at all. Moreover, dandelion has not been shown to increase the urinary loss of potassium; it is, in fact, a rich source of potassium. Given these facts, it is not surprising that no published reports exist confirming this proposed interaction.

However, the debate doesn’t stop here, for many other herbs have diuretic effects. And a number of them have a long and venerable history of use as part of what would have been called “conventional medicine” in its day. To understand the issues we face today, it’s helpful to know about the history of herbal diuretics.

Diuretic use in history

Diuretics have been used medicinally for thousands of years: Egyptian medical papyri from as far back as 1550 b.c. contain references to them. The primary indication for using diuretics in ancient times was to eliminate edema, which can result from congestive heart failure (formerly called dropsy), kidney disease, or cirrhosis of the liver. Traditional doctors and herbalists also used diuretics for detoxification and to treat kidney stones.

Most diuretics throughout history have been derived from plants. One of the best examples is an extract of juniper berries (Juniperus communis), which was developed and marketed by a Dutch pharmacist in the 1500s. This extract later came to be called gin. Juniper berries contain a volatile oil that increases urinary flow through its toxic effect on the kidneys.

During the same time period, the diuretic effects of tea and coffee were realized. Researchers later determined that the active ingredients in these two beverages were a group of compounds called xanthine alkaloids, which include caffeine, theobromine, and theophylline. Although most people think of caffeine for its stimulant properties, it remains one of the most potent over-the-counter diuretics. Xanthines appear to stimulate urinary flow by a direct effect on the kidneys, as well as by increasing heart rate.

Other traditional herbal diuretics include parsley (Petroselinum crispum), birch (Betula pendula), lovage (Levisticum officinale), buchu (Barosma betulina), couch grass (Agropyron repens), corn silk (Zea mays), celery (Apium graveolens), gravel root (Eupatorium purpureum), horsetail (Equi-setum arvense), elder flower (Sambucus nigra), squill (Scilla maritima) and ma huang (Ephedra spp.). These herbs vary widely in their effectiveness and in their mechanism of action.

Along with plant-based therapies, various forms of mercury were also included in diuretic remedies, beginning as far back as the sixteenth century when calomel (mercurous chloride) first became popular. Despite their toxicity, mercury compounds were the mainstay of conventional diuretic therapy for hundreds of years. All of this changed with the discovery of the drug chlorothiazide in the late 1950s. Unlike mercury, which worked by depressing overall kidney function, chlorothiazide had a much more specific effect: It inhibited the reabsorption of sodium, which led to the excretion of water. And it did this with minimal toxicity (in dramatic contrast to mercury).

Safer, gentler diuretics

Needless to say, the class of drugs based on the discovery of chlorothiazide soon became the standard of care for the treatment of edema and high blood pressure. Although these drugs were considered safe for long-term use, they did have at least one serious side effect–they caused excessive losses of potassium (and in some cases sodium) in the urine. Without proper monitoring and replacement of potassium, serious, even life-threatening complications could result. Knowing this helps us understand why pharmacologists are concerned that herbal diuretics could do the same thing or potentially enhance the problem caused by the drug.

As it turns out, most herbal diuretics work by an entirely different mechanism. Many herbalists believe that a more accurate term is “aquaretic,” meaning that the herb works by increasing the excretion of water from the kidneys, but not by increasing the loss of sodium, potassium, or other electrolytes. In other words, herbal diuretics do not typically cause the same side effects as the drugs. Actually, given the high potassium content of dandelion and many other herbs, it’s possible that these botanical medicines would provide an ideal complement to prescription diuretics.

Admittedly, there are very few good ­scientific studies that have explored this information in the kind of detail that pharmacologists prefer. Meanwhile, many herbalists have continued with a tradition begun hundreds of years ago and use herbal diuretics extensively to treat a number of health-related problems. Wouldn’t it be more useful to find ways to incor­porate these traditions into modern ­medical practice instead of making sweeping recommendations to discard them as relics?

By Robert Rountree

Robert Rountree, M.D., is a physician at the Helios Health Center in Boulder, Colorado, where he practices integrative medicine. He is coauthor of Smart Medicine for a Healthier Child (Avery, 1994), and an Herb Research Foundation advisory board member.


Hawkins, E. “And the good herb taketh away.” Nutrition Science News 1999, 4(10): 482-486.
Miller, L. “Herbal medicinals: selected clinical considerations focusing on known or potential drug-herb interactions.” Archives of Internal Medicine 1998, 158: 2200-2211.

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