How does foxglove affect the body? A deep dive into its cardiac effects and dangers

October 7, 2025 •

5 min read

In the 18th century, physician William Withering famously documented the use of foxglove, a plant that all parts are highly poisonous, as an effective folk remedy for "dropsy" (congestive heart failure). This discovery revealed the complex ways how does foxglove affect the body, possessing powerful cardiac glycosides that both heal and harm depending on the dose.

Quick Summary

Foxglove contains cardiac glycosides like digoxin that inhibit the sodium-potassium pump, increasing cardiac muscle contraction. This strengthens the heart's pumping action at therapeutic doses, but in toxic amounts, it can cause severe arrhythmias, nausea, and visual disturbances.

Key Points

Dual Nature: Foxglove contains cardiac glycosides like digoxin, which are both potent heart medications and deadly poisons, depending on the dosage.
Cellular Mechanism: The plant's compounds inhibit the sodium-potassium pump in heart cells, leading to increased intracellular calcium and stronger, but potentially erratic, heartbeats.
Therapeutic Use: When precisely controlled as a medication, foxglove derivatives treat conditions like congestive heart failure and atrial fibrillation by strengthening heart contractions and regulating rhythm.
Symptoms of Poisoning: Ingestion can cause severe gastrointestinal issues, visual disturbances (like seeing yellow halos), and dangerous cardiac arrhythmias.
Narrow Therapeutic Window: The margin of safety is very small, making the wild plant extremely dangerous for self-medication.
Antidote Available: For severe poisoning, a specific antidote called digoxin immune fab can be administered to neutralize the toxins.

The foxglove plant (Digitalis purpurea), while known for its beautiful bell-shaped flowers, is notoriously dangerous due to its concentration of cardiac glycosides. These powerful compounds, including digitoxin and the pharmaceutical drug digoxin, have a narrow therapeutic index—meaning the difference between a therapeutic dose and a toxic dose is very small. This article explores the dual nature of foxglove's effects on the human body, detailing its pharmacological mechanism, therapeutic benefits, and severe toxicity.

The Mechanism of Action: How Cardiac Glycosides Work

The primary mechanism behind how does foxglove affect the body lies in its active compounds' ability to interact with the heart's cellular machinery. The key target is the sodium-potassium pump ($Na^+/K^+$ ATPase), an enzyme located in the cell membranes of heart muscle cells (myocytes).

Inhibition of the $Na^+/K^+$ Pump: Cardiac glycosides reversibly bind to and inhibit the sodium-potassium pump. This critical pump is responsible for maintaining the electrochemical gradient across the cell membrane by pumping sodium ions ($Na^+$) out and potassium ions ($K^+$) in.
Increased Intracellular Sodium: When the pump is inhibited, sodium ions build up inside the myocyte.
Sodium-Calcium Exchange: The increased intracellular sodium reduces the efficiency of another cellular exchanger, the sodium-calcium exchanger, which typically removes calcium ($Ca^{2+}$) from the cell in exchange for sodium.
Elevated Intracellular Calcium: The resulting increase in intracellular calcium ions leads to a greater release of calcium from the sarcoplasmic reticulum during each cardiac action potential.
Stronger Heart Contractions: The higher concentration of calcium available to the heart's contractile proteins (actin and myosin) results in a more forceful myocardial contraction. This is known as a positive inotropic effect.
Slowed Heart Rate: Digoxin also exerts a vagomimetic effect, stimulating the parasympathetic nervous system. This action slows down the electrical signals passing through the sinoatrial (SA) and atrioventricular (AV) nodes, decreasing the heart rate and controlling irregular rhythms.

Therapeutic Applications of Digitalis

Historically and still, in some cases, the cardiac glycosides from foxglove are used in carefully controlled pharmaceutical form (like digoxin) to treat specific heart conditions. The benefits derive from its ability to enhance the heart's pumping efficiency and regulate its rhythm.

Congestive Heart Failure (CHF): In patients with heart failure with reduced ejection fraction, digoxin increases the force of contraction, improving blood circulation and reducing symptoms like swelling.
Atrial Fibrillation (AFib): For patients with certain types of AFib, digoxin helps control the ventricular response rate by slowing down the electrical conduction through the heart's AV node. This provides rate control when other medications, like beta-blockers, are ineffective or contraindicated.

The Dark Side: Foxglove Toxicity

The same powerful compounds that offer therapeutic benefits can cause severe, and often fatal, poisoning if ingested improperly. All parts of the foxglove plant are toxic, and even a small amount can be dangerous.

Gastrointestinal and Neurological Symptoms

The initial signs of toxicity often include gastrointestinal distress and a range of neurological effects.

Nausea, vomiting, and diarrhea: These are among the first symptoms to appear after ingestion.
Vision disturbances: A classic sign of digitalis toxicity is blurred vision and the perception of yellow-green halos around objects (xanthopsia), famously theorized to have influenced artist Vincent van Gogh.
Neurological effects: Confusion, disorientation, depression, lethargy, and sometimes hallucinations or convulsions can occur in more severe cases.

Cardiac Toxicity

The most dangerous effects of foxglove poisoning are on the heart. An overdose disrupts the electrical signals and can cause virtually any type of arrhythmia.

Arrhythmias: Digitalis toxicity can lead to irregular heart rhythms, bradycardia (abnormally slow heart rate), and various heart blockages.
Severe Consequences: In severe cases, this cardiotoxicity can lead to ventricular fibrillation, cardiac arrest, and death.

Comparison: Therapeutic vs. Toxic Effects


Feature	Therapeutic Dose (Digoxin)	Toxic Dose (Foxglove Poisoning)
Heart Muscle Contraction	Increased strength, leading to better cardiac output.	Uncontrolled contractions leading to arrhythmias.
Heart Rate	Decreased and controlled, beneficial for certain arrhythmias.	Dangerously slow (bradycardia) or chaotic and life-threatening.
Visual Effects	None, at appropriate doses.	Yellow-green halos (xanthopsia) and blurred vision.
Gastrointestinal Effects	Mild, may include slight nausea; can be a sign of toxicity if severe.	Prominent and severe nausea, vomiting, diarrhea.
Neurological Effects	None, at appropriate doses.	Confusion, hallucinations, depression, fatigue.
Margin of Safety	Narrow therapeutic window, requires careful monitoring.	Zero margin for self-medication; extremely dangerous.
Potassium Levels	Closely monitored, as low potassium increases toxicity risk.	Often associated with dangerously high or fluctuating potassium levels.

Pharmacokinetics and Drug Interactions

For pharmaceutical digoxin, the drug is primarily eliminated by the kidneys, which means patients with impaired renal function require lower doses to prevent accumulation and toxicity. Other medications can also interact significantly with digoxin, altering its absorption or clearance. For example:

Diuretics and Laxatives: Can cause hypokalemia (low potassium), which increases the risk of digitalis toxicity.
Certain Antibiotics: Tetracycline and macrolide antibiotics can increase digoxin absorption and plasma levels.
Antiarrhythmic Medications: Drugs like quinidine, verapamil, and amiodarone can increase serum digoxin concentrations.

Treatment for Foxglove Poisoning

Ingestion of foxglove is a medical emergency. Treatment focuses on preventing further absorption of the toxins and managing the severe cardiac effects. Management strategies include:

Emergency Care: Immediate hospitalization and monitoring of vital signs and cardiac rhythm (ECG).
Decontamination: Administering activated charcoal to prevent the stomach and intestines from absorbing more toxins. Gastric lavage may also be used in some cases.
Antidote: The specific antidote, digoxin immune fab (Digibind), consists of antibody fragments that bind to the digitalis molecules, effectively neutralizing them and reversing their effects on the heart.
Symptomatic Support: Managing arrhythmias and addressing electrolyte imbalances, especially hyperkalemia (high potassium).

Conclusion

The foxglove plant presents a stark paradox: it is the source of lifesaving medication for heart conditions but is also an extremely potent poison. The question of how does foxglove affect the body reveals a sophisticated pharmacological interaction involving the cellular sodium-potassium pump, influencing cardiac muscle contraction and electrical conduction. While pharmaceutical derivations like digoxin offer controlled, therapeutic benefits under strict medical supervision, the raw plant is unpredictably dangerous due to its variable concentration of toxins and narrow therapeutic window. The history and clinical use of digitalis underscore the critical importance of a precise understanding of pharmacology and the dangers of self-medication with herbal remedies.

For further information on the mechanism of digoxin and digitalis toxicity, consult the National Center for Biotechnology Information (NCBI) database on cardiac glycosides.

Frequently Asked Questions

Yes, ingesting any part of the foxglove plant can be fatal. The plant contains cardiac glycosides that can cause severe heart arrhythmias, cardiac arrest, and death.

If a child eats foxglove, seek immediate emergency medical attention. Children are particularly susceptible to the plant's toxins, which can cause severe cardiac and neurological effects, even in small amounts.

The primary mechanism is the inhibition of the $Na^+/K^+$ ATPase pump in heart muscle cells. This leads to an increase in intracellular sodium and, consequently, an increase in calcium, which enhances cardiac muscle contraction.

The initial symptoms typically include nausea, vomiting, and diarrhea. As the toxicity progresses, more serious cardiac and neurological signs will appear.

It is not safe to touch a foxglove plant without gloves, as the toxins can be absorbed through the skin, although absorption is typically minimal unless the plant is handled for prolonged periods or by individuals with skin sensitivities. Always wash hands thoroughly after handling.

Treatment for foxglove poisoning involves immediate supportive care in an emergency setting. This may include decontamination with activated charcoal and administration of the specific antidote, digoxin immune fab.

No, foxglove is extremely dangerous and should never be used as a home remedy. Its narrow therapeutic index makes it impossible for an individual to measure a safe dose, and the risk of fatal poisoning is very high.

Foxglove is the plant (Digitalis) containing the toxins. Digoxin is a purified, pharmaceutical drug derived from the plant (Digitalis lanata) that is precisely dosed for medical use under strict supervision.