Think of Foxglove as the Femme Nikita of herbs— beautiful, potentially deadly, and invaluable when used properly. Foxglove contains substances that are among the most potent heart treatment drugs used today, but they can be lethal if used incorrectly.
Despite the danger, physicians and herbalists have long turned to foxglove to treat a variety of disorders, including tuberculosis and edema. But it wasn’t until the twentieth century that health practitioners made the link between foxglove and congestive heart failure (CHF), and that medicines derived from the plant were developed into prescription drugs.
Foxglove contains the cardiac glycosides digitoxin (from Digitalis purpurea and D. lantana) and digoxin (from D. lantana). All of foxglove’s glycosides, known collectively as digitalis, increase the force of heart contractions, leading to more efficient movement of blood through the heart and giving the heart more resting time between contractions. Glycosides also correct abnormal rhythms such as atrial fibrillation and atrial flutter, and act as a diuretic, an effect that arises more from improved circulation than from a direct impact on the kidneys.
While such qualities make digitalis a valuable treatment for CHF, it has drawbacks. One is a narrow therapeutic window that allows desired outcomes only within a small dosage range. Amounts higher than the range can be deadly or, at minimum, cause gastrointestinal discomforts such as depressed appetite, nausea, and vomiting; neurological side effects, such as dizziness, fatigue, and hallucinations; and cardiac system problems, including abnormal heart rhythms. To underscore the deadly power digitalis can wield, between 1993 and 1995, four previously healthy men, including a twenty-three-year-old and a twenty-six-year-old, died after taking an aphrodisiac that left abnormally high amounts of digoxin in their blood.
In addition, foxglove is by itself a poisonous plant. Do NOT eat it out of your garden, nor try to make your own medicines from it. And use digitalis-derived medicines only as recommended by your physician, who will carefully monitor you for ill effects. Practitioners who emphasize natural healing usually prefer to bolster a failing heart with other, milder herbs, notably hawthorn (Crataegus spp).
Foxglove’s Long and Tangled Past
Despite the drawbacks, the fact is that foxglove has contributed enormously to modern medicine.
The name foxglove probably comes from the Anglo-Saxon word foxes-glew, meaning fox music. Apparently, the bell-like flowers resembled an ancient musical instrument whose bells hung from an arched support. In Scandinavian dialects, the name means foxes-bell.
Herbalists first began experimenting with foxglove centuries ago. They created a powder of the leaves and prescribed it for internal cleansing. They noted a constellation of side effects, ranging from vomiting to death, and described foxglove as a violent medicine.
Medieval healers used the plant externally, and records from the early Renaissance focus on foxglove’s external use as an ointment for treating wounds, ulcers, and other conditions. Foxglove was first mentioned to treat “feebleness of the heart” in 1526 by Peter Treveris in his Grete Herball.
The sixteenth-century German botanist Leonhardt Fuchs wrote about foxglove in an important herbal published in 1542. To him, the flowers resembled the single digit of a glove (fingerhut in German), so he gave the plant its genus name, Digitalis—which contains the root word digit, or finger.
In Theatrum Botanicum published in London in 1640, John Parkinson recommended the herb for tuberculosis of the lymph nodes in the neck. People also called this malady “the King’s Evill” because they believed that a royal touch could cure it. “The herb bruised or the juice made up into an ointment and applied to the place, hath been found by late experience to be available for the King’s Evill,” wrote Parkinson, an herbalist and apothecary.
Until the late eighteenth century, information on foxglove consisted of anecdotes about its use as a folk medicine. But in 1785, the British physician William Withering introduced the herb to the medical establishment with the publication of An Account of the Foxglove and Some of Its Medical Uses: With Practical Remarks on Dropsy, and Other Diseases. Withering came to know foxglove as an important medicinal after he heard a rumor of foxglove’s use by “an old woman in Shropshire.” He recognized that digitalis affected the heart, but he mistakenly believed that it acted primarily on the kidneys as a diuretic.
After Withering’s discovery, foxglove leaf became a standardly prescribed drug in medical practice, primarily as a diuretic to treat “dropsy,” an excess accumulation of fluid in connective tissue, known today as edema. It was also mistakenly prescribed for maladies ranging from asthma to insanity. But physicians soon began to observe its effects on the heart. In his 1789 edition of the Edinburgh New Dispensatory, Andrew Duncan wrote, “During its operation it has often very remarkable influence in rendering the pulse slower; and it frequently excites very considerable vertigo, and an affection of vision.”
A More Precise Picture
By the mid-nineteenth century, physicians viewed foxglove as a narcotic, diuretic, and sedative with remarkable effects on the heart, including reducing the frequency of the pulse. A clearer understanding of digitalis came as the pharmacy sciences shifted from focusing on the identification and standardization of drugs to studying their effect on living organisms.
In 1883, Oswald Schmiedeberg, a renowned German pharmacologist, published findings that attributed foxglove’s effects to its glycosides. And in 1905, the British Medicinal Journal published results of experiments conducted by Sir James Mackenzie, a Scottish physician who used a pulse-measuring device to record the effects of digitalis.
From the late 1800s to about 1930, researchers more precisely isolated cardiac glycosides such as digitoxin and digoxin, and these compounds came to be manufactured and prescribed as drugs. Although physicians knew that the compounds could be toxic, they valued them for their potent effect on the heart—and they still do. Thanks to Withering, an observant and open-minded physician, foxglove has evolved from a folk remedy to a powerful medicine—one that has saved countless lives.
Steven Foster, an Herbs for Health editorial adviser, is author of Herbs for Your Health (Interweave Press, 1996), and 101 Medicinal Herbs—An Illustrated Guide, due this fall from Interweave.