One preliminary trial has suggested that St. John’s  wort(Hypericum perforatum) may reduce blood levels of digoxin.¹ In this study, healthy volunteers took digoxin for five days, after which they added 900 mg per day of St. John’s wort while continuing the daily digoxin. A normal blood level of digoxin was reached after five days of taking the drug, but this level dropped significantly when St. John’s wort was added. This may have occurred because certain chemicals found in St. John’s wort activate liver enzymes that are involved in the elimination of some drugs.^{2 , 3} Until more is known, people taking digoxin should avoid St. John’s wort.

As pleurisy root and other plants in the Aesclepius genus contain cardiac glycosides, it is best to avoid use of pleurisy root with heart medications such as digoxin.⁴

Sarsaparilla may increase the absorption of digitalis and bismuth, increasing the chance of toxicity.⁵

Loss of potassium due to cascara (Rhamnus purshiani cortex) abuse could theoretically increase the effects of digoxin and other similar heart medications, with potentially fatal consequences. However, no cases of such an interaction have yet been reported.

Digitalis (Digitalis purpurea) refers to a group of plants commonly called foxglove that contain chemicals with actions and toxicities similar to digoxin. Digitalis was used as an herbal medicine to treat some heart conditions before the drug digoxin was available. Some doctors continue to use digitalis in the United States, and it is used as an herbal medicine in other countries as well. Due to the additive risk of toxicity, digitalis and digoxin should never be used together.

People taking digoxin require regular monitoring of serum digoxin levels. In one report, addition of a product identified as Siberian ginseng to stable, therapeutic digoxin treatment was associated with dangerously high serum digoxin levels.⁶ The patient never experienced symptoms of digoxin toxicity. Laboratory analysis found the product was free of digoxin-like compounds but the contents were not further identified. This report may reflect an interaction of eleuthero with the laboratory test to cause a falsely elevated reading, rather than actually increasing digoxin levels.

Potassium deficiency increases the risk of digoxin toxicity. Excessive use of licorice plant or licorice plant products may cause the body to lose potassium.⁷ Artificial licorice flavoring does not cause potassium loss. People taking digoxin should read product labels carefully for licorice plant ingredients.

Hawthorn (Crataegus oxyacantha, Crataegus monogyna) (leaf with flower) extract is approved in Germany to treat mild congestive heart failure .⁸ Congestive heart failure is a serious medical condition that requires expert medical management rather than self-treatment. Due to the narrow safety index of digoxin, it makes sense for people taking digoxin for congestive heart failure to consult with their doctor before using hawthorn-containing products. Reports of hawthorn interacting with digitalis to enhance its effects have not been confirmed.

People needing digoxin may have low levels of potassium or magnesium,⁹ increasing the risk for digoxin toxicity. Digoxin therapy may increase magnesium elimination from the body.¹⁰ People taking digoxin may benefit from magnesium supplementation.¹¹ Medical doctors do not commonly check magnesium status, and when they do, they typically use an insensitive indicator of magnesium status (serum or plasma levels). The red blood cell magnesium level may be a more sensitive indicator of magnesium status, although evidence is conflicting. It has been suggested that 300–500 mg of magnesium per day is a reasonable amount to supplement.¹²

Use of buckthorn (Rhamnus catartica, Rhamnus frangula, Frangula alnus) or alder buckthorn for more than ten days consecutively may cause a loss of electrolytes (especially the mineral potassium). Loss of potassium may increase the toxicity of digitalis-like medications with potentially fatal consequences.¹³

Use of buckthorn (Rhamnus catartica, Rhamnus frangula, Frangula alnus) or alder buckthorn for more than ten days consecutively may cause a loss of electrolytes (especially the mineral potassium). Loss of potassium may increase the toxicity of digitalis-like medications with potentially fatal consequences.¹⁴

Medical doctors prescribing digoxin also check for potassium depletion and prescribe potassium supplements if needed. Potassium transport from the blood into cells is impaired by digoxin.¹⁵ Although digoxin therapy does not usually lead to excess potassium in the blood (hyperkalemia), an overdose of digoxin could cause a potentially fatal hyperkalemia.¹⁶ People taking digoxin should therefore avoid taking potassium supplements, or eating large quantities of fruit (e.g., bananas), unless directed to do so by their doctor. On the other hand, many people taking digoxin are also taking a diuretic; in these individuals, increased intake of potassium may be needed. These issues should be discussed with a doctor.

Bisacodyl , a laxative similar in action to senna (Cassia senna, Cassia angustifolia), givenwith digoxin decreased serum digoxin levels in healthy volunteers compared with digoxin alone.¹⁷ In patients taking digoxin, laxative use was also associated with decreased digoxin levels.¹⁸ In addition, concern has been expressed that overuse or misuse of senna may deplete potassium levels and increase both digoxin activity and risk of toxicity.¹⁹ However, overuse of senna could also decrease digoxin activity because, as noted, laxatives can decrease the levels of the drug.