Herb Drug Mix: Heart Safety

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Some herbalists have combined digoxin and hawthorn for years 

Here’s an ironic twist: an herb is made into a popular pharmaceutical drug, and later patients are warned about taking it with other herbs.

I’m talking about foxglove (Digitalis purpurea), the source of the active ingredient in the heart medicine digoxin. Since its popularization by William Withering in 1785, foxglove and its derivatives have been used to successfully treat congestive heart failure (CHF) and arterial fibrillation.

Cardiac glycosides defined 

Foxglove contains cardiac glycosides, molecules that are a combination of sugar and other organic substances. A potent medicine, glycosides block an enzyme that regulates electrical activity in the membranes of heart tissue. Small doses create ­positive effects by enabling the heart to ­contract more slowly and efficiently. But cardiac glycosides are also biological toxins and excessive doses can cause serious problems. By interfering with normal electrical rhythms, they can make the heart beat too slowly or generate extra heartbeats.

Consequently, patients taking digoxin require close monitoring. Many other medications routinely prescribed for heart problems can amplify the toxicity of cardiac ­glycosides, so dosages must be carefully adjusted when used in combination with digoxin. Cardiac glycosides can also cause negative side effects when sodium, potassium, calcium, and magnesium levels are too low, so they must be monitored as well. This means that conditions causing loss of fluids and salts—such as dehydration from diarrhea or use of diuretics-—can induce side effects from digoxin.

Let’s contrast foxglove to hawthorn (Crataegus spp.), another cardiac herb. Hawthorn has a long, venerable history as a folk medicine. It’s used to treat many of the same ailments as foxglove.

Hawthorn: a heart tonic 

Numerous medical studies document hawthorn’s ­ability to increase the strength of heart muscle contractions while simultaneously relaxing and dilating blood vessels. This may explain why it seems to decrease the symptoms of congestive heart failure, alleviate angina (chest pain from oxygen-starved heart muscles), lower blood pressure, and help normalize irregular heart rhythms.

But a crucial distinction needs to be made between the two herbs: Instead of producing a druglike or potentially toxic effect, hawthorn acts as a tonic, nourishing heart muscles. Some herbalists call hawthorn “food for the heart.’’ When taken in commonly recommended dosages (500 to 1,000 mg of the standardized extract daily, usually in capsule form), side effects are rare and limited to low blood pressure and some sedation.