What does foxglove do to the human body?: A look at the medicine and the poison

October 11, 2025 •

4 min read

First documented for medicinal use in 1785 by William Withering, all parts of the foxglove plant are poisonous, containing cardiac glycosides that powerfully affect the human body. While highly dangerous for self-medication, these compounds are the source of the life-saving prescription drug digoxin.

Quick Summary

Foxglove contains potent cardiac glycosides that dangerously influence heart function, but a refined derivative, digoxin, is used medically to treat heart failure and arrhythmias. Uncontrolled ingestion is extremely toxic, causing a range of symptoms from visual disturbances to fatal cardiac arrest.

Key Points

Cardiac Glycosides: Foxglove contains highly toxic cardiac glycosides, such as digoxin and digitoxin, that directly impact the heart muscle.
Mechanism of Action: These compounds inhibit the sodium-potassium pump in heart cells, increasing intracellular calcium, which strengthens the heart's contractions and slows its rate.
Digoxin Medication: A purified and carefully dosed derivative of foxglove, digoxin, is a prescription drug used to treat heart failure and irregular heart rhythms.
Symptoms of Poisoning: Ingesting the plant can cause severe symptoms, including nausea, vomiting, blurred vision, colored halos around lights (xanthopsia), a dangerously slow heartbeat, and cardiac arrest.
Narrow Therapeutic Index: The difference between a therapeutic dose of the active compounds and a toxic dose is very small, making the raw plant extremely dangerous for self-medication.
Medical Emergency: Any ingestion of the foxglove plant should be considered a medical emergency requiring immediate attention from a healthcare professional or Poison Control.

The seemingly innocuous and beautiful foxglove plant, with its tall spires of thimble-like flowers, harbors a dangerous secret. Within its leaves, stems, flowers, and seeds lie powerful chemical compounds known as cardiac glycosides. These substances have a profound and dualistic effect on the human body, serving as both a source of life-saving heart medication and a deadly poison. Understanding this complex relationship requires exploring the plant's mechanism of action, its refined medical application, and the very real dangers of uncontrolled exposure.

The Dual Nature of Foxglove

The foxglove plant, scientifically known as Digitalis purpurea and Digitalis lanata, produces a cocktail of chemical compounds, including digitoxin and digoxin. These substances are powerful cardiotoxins, meaning they have a specific and potent effect on the heart muscle. The therapeutic index of these compounds—the ratio between a toxic dose and a therapeutic dose—is very narrow, making accidental overdose a significant risk. This narrow margin is precisely why the plant is so dangerous for casual handling or ingestion.

The Mechanism of Action on the Heart

The primary way cardiac glycosides affect the heart is by interfering with the sodium-potassium pump ($Na^+/K^+$-ATPase), a vital enzyme found in the membrane of heart muscle cells. Normally, this pump moves potassium ions into the cell and sodium ions out. When cardiac glycosides from foxglove bind to and inhibit this pump, the following cascade of events occurs:

Sodium buildup: The pump stops functioning correctly, causing sodium levels inside the heart cells to increase.
Calcium influx: This buildup of sodium alters the function of another membrane protein, the sodium-calcium exchanger. The exchanger begins to pump more sodium out and, crucially, more calcium into the cell.
Stronger contractions: The increased intracellular calcium concentration leads to stronger, more forceful contractions of the heart muscle. This can be beneficial in a controlled medical setting but is highly dangerous in an overdose.
Slower heart rate: Cardiac glycosides also increase the activity of the vagus nerve, which slows the electrical impulses passing through the heart's atrioventricular (AV) node. This effect is used to control rapid heart rates in certain conditions.

Medical Applications: The Drug Digoxin

The understanding of foxglove's effects was pioneered in the late 18th century and has led to the development of the widely used prescription drug, digoxin (Lanoxin). Derived from the woolly foxglove (Digitalis lanata), digoxin is a highly purified and standardized version of the plant's active compounds. It is not a home remedy; it is a carefully controlled medication with a strict dosing regimen and requires regular monitoring by a healthcare professional.

Digoxin is primarily used to treat two major heart conditions:

Congestive Heart Failure (CHF): By increasing the force of the heart's contractions, digoxin helps the heart pump blood more effectively, improving circulation and reducing fluid buildup (edema) in the body.
Atrial Fibrillation: Digoxin can help control the heart rate in patients with this irregular and often rapid heartbeat by slowing the electrical conduction through the AV node.

Dangers of Ingestion: Foxglove Poisoning

All parts of the foxglove plant—leaves, stems, flowers, and even seeds—are toxic. Accidental ingestion is a medical emergency that can lead to severe poisoning and death. Common scenarios include children ingesting the appealing bell-shaped flowers or adults mistaking foxglove leaves for other edible herbs, such as comfrey.

Symptoms of foxglove poisoning can vary based on the amount ingested but often follow a predictable pattern. These signs include:

Gastrointestinal Distress: Nausea, vomiting, diarrhea, and stomach pain often occur first.
Cardiac Symptoms: An irregular or slow heartbeat (bradycardia), low blood pressure (hypotension), and in severe cases, collapse or cardiac arrest.
Neurological Effects: Headaches, confusion, disorientation, lethargy, and drowsiness.
Visual Disturbances: A classic sign of digitalis toxicity is visual changes, including blurred vision, seeing yellow-green halos around objects (xanthopsia), and other perceptual distortions.

Clinical Management of Toxicity

In cases of suspected foxglove poisoning, immediate medical attention is critical. Emergency treatment focuses on stabilizing the patient and mitigating the toxic effects. This may involve:

Monitoring: Closely observing the patient's vital signs, including heart rate, blood pressure, and ECG.
Activated Charcoal: Administering activated charcoal to bind to and prevent further absorption of the toxins in the stomach.
Medications: Using specific antidotes, such as digoxin-specific antibody fragments (Fab), to reverse the effects of the cardiac glycosides in severe cases.

Foxglove vs. Digoxin: A Crucial Comparison

Despite both originating from the same plant, the distinction between the unprocessed foxglove plant and the refined digoxin medication is paramount. The table below highlights the key differences that underscore why one is a life-saving tool and the other is a potential hazard.


Feature	Wild Foxglove Plant	Prescription Digoxin
Safety	Highly poisonous for ingestion	Safe when prescribed and monitored by a doctor
Source of Active Compound	Inconsistent concentration across different plant parts, age, and species	Purified, standardized, and regulated concentration
Dosage Control	Impossible to control; toxic dose is very close to effective dose	Precisely measured and controlled to minimize toxicity
Medical Use	Historically used in folk medicine, but extremely risky and unsafe for self-medication	Modernly used to treat specific cardiac conditions like CHF and atrial fibrillation
Toxicity Profile	Contains a mix of different cardiac glycosides	Contains only the refined, active compound

Conclusion

What does foxglove do to the human body? The answer is a potent and cautionary tale of pharmacology. The plant's cardiac glycosides possess the power to either regulate and strengthen a failing heart or to fatally disrupt its rhythm. While the refined and controlled compound, digoxin, is an essential tool in modern medicine for treating conditions like congestive heart failure and atrial fibrillation, the raw foxglove plant remains a dangerous poison. The extreme toxicity and narrow therapeutic window serve as a critical reminder that while nature provides many powerful substances, their safe use demands scientific refinement and strict medical supervision. The elegant garden flower should be enjoyed from a distance and never consumed in any form.

For additional information on plant toxicity, please consult authoritative resources like the Poison Control Center.

Frequently Asked Questions

Touching a foxglove plant is generally not dangerous, though some people may experience a mild rash from contact with the plant's hairs. Ingestion, however, is highly toxic and should be avoided.

The onset of symptoms can vary depending on the amount ingested but typically appears relatively quickly, beginning with gastrointestinal distress like nausea and vomiting, followed by more serious cardiac or neurological effects.

Digitalis is a genus of plants, including foxglove, and also refers to the cardiac glycosides extracted from it. The medication digoxin is a highly purified and controlled form of these glycosides, whereas the raw plant is inconsistently potent and highly toxic.

Treatment for poisoning involves emergency medical intervention, including monitoring vital signs, administering activated charcoal to limit absorption, and in severe cases, using digoxin-specific antibody fragments to counteract the toxins.

Digoxin remains in use because it is a highly effective medication for specific heart conditions like congestive heart failure and atrial fibrillation. Unlike the raw plant, the prescription drug is carefully dosed, monitored, and its benefits outweigh the risks when used under medical supervision.

Yes, all parts of the foxglove plant are toxic to pets, including dogs, cats, and livestock. If you suspect your pet has ingested any part of a foxglove plant, contact your veterinarian or a pet poison helpline immediately.

Initial symptoms often include stomach upset, nausea, vomiting, and diarrhea. These can quickly progress to more serious cardiac and neurological effects.