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.