There is no single gram-weight of foxglove that reliably kills a person, and that uncertainty is part of what makes the plant so dangerous. Foxglove (Digitalis purpurea) contains cardiac glycosides, chemicals that disrupt the heart’s electrical rhythm, and the concentration of those compounds varies enormously from leaf to leaf, plant to plant, and season to season. A few leaves brewed into tea have hospitalized adults, while in at least one documented case an entire plant’s worth of leaves was consumed without proving fatal. What determines the outcome has less to do with a specific dose threshold and more to do with a chain of variables including which part of the plant was eaten, the person’s body weight and heart health, and how quickly they received medical care.
Why No One Can Name a Precise Lethal Dose
Foxglove’s toxicity comes primarily from digitoxin and several related cardiac glycosides concentrated in the leaves, flowers, stems, and seeds. Unlike a pharmaceutical pill with a standardized amount of active ingredient, a foxglove leaf is a biological product whose glycoside content fluctuates with the plant’s age, growing conditions, and the time of year it was harvested. Upper leaves tend to be more concentrated than lower ones, and dried leaves can be more potent per gram than fresh ones because the water weight is gone while the glycosides remain.
In one published case, a 34-year-old woman bought a foxglove plant online and used all of its leaves to brew a tea she drank over several hours. Her plasma digoxin concentration measured well above the therapeutic range at 3.53 nmol/l (the therapeutic reference range for digoxin, a pharmaceutical relative of the plant’s glycosides, is roughly 0.77–1.50 nmol/l). Despite that level, she remained stable, did not require the specific antidote, and survived with supportive care.1PubMed Central. A case of intoxication with tea made from Digitalis purpurea In a different case, a woman who mistook foxglove for comfrey developed a heart rate of just 54 beats per minute, dangerously high potassium, and a lethal heart rhythm disturbance, and died.2PubMed. Fatal cardiac glycoside poisoning due to mistaking foxglove for comfrey Both involved eating or drinking the plant’s leaves. The wildly different outcomes illustrate why toxicologists do not quote a neat “X grams = death” figure for foxglove.
What is known is that the margin between a therapeutic dose of pharmaceutical digitalis and a toxic one has always been razor-thin. Even in controlled medical settings, digoxin’s therapeutic range sits uncomfortably close to the concentration at which dangerous side effects begin. For a wild plant with unpredictable potency, that narrow margin essentially disappears. Any amount of foxglove ingested by a person who is not under medical supervision should be treated as potentially lethal.
How Foxglove Disrupts the Heart
Foxglove’s cardiac glycosides work by blocking a pump in heart-muscle cells called the sodium-potassium ATPase. This pump normally moves sodium out of the cell and potassium in, maintaining the electrical balance the heart relies on to beat in a coordinated rhythm. When the pump is blocked, sodium builds up inside the cell. That sodium buildup interferes with another transporter responsible for removing calcium, so calcium accumulates in the cell as well.3PubMed Central. The mechanism of action of digoxin requires the sodium-dependent inactivation of the sodium-calcium exchanger
In small, controlled doses, this extra calcium makes the heart squeeze harder, which is why digitalis has been used as a heart-failure drug for centuries. In an uncontrolled dose from a plant, the calcium overload sends the heart’s electrical system haywire. Cells that should fire in sequence start firing on their own, producing abnormal rhythms that range from a dangerously slow heartbeat to chaotic, life-threatening patterns. At the same time, potassium leaks out of cells into the bloodstream, creating hyperkalemia, a condition that compounds the cardiac danger.
The First Warning Signs
Foxglove poisoning does not usually begin with a cardiac crisis. The earliest symptoms are gastrointestinal and can look deceptively mild: nausea, vomiting, abdominal pain, and diarrhea. In two documented accidental poisonings, one patient who drank foxglove tea presented with nausea, vomiting, and dizziness, while a second patient who had eaten foxglove leaves mistaken for spinach arrived with nausea, vomiting, lethargy, and confusion.4PubMed Central. Two cases of cardiac glycoside poisoning from accidental foxglove ingestion These initial symptoms can start within a couple of hours of ingestion and are easy to dismiss as food poisoning or a stomach bug.
The danger in that early phase is complacency. If someone has unknowingly eaten foxglove and the only symptoms are nausea and vomiting, they or the people around them may not seek emergency care quickly enough. What distinguishes foxglove from ordinary food poisoning is that the gastrointestinal symptoms are the opening act for a cardiac event that can follow hours later. In one outbreak involving nine patients who drank herbal tea made from foxglove leaves misidentified as comfrey, all initially presented with nausea, vomiting, diarrhea, and dizziness. Significant cardiotoxicity developed later in the three patients who also had elevated potassium levels.5PubMed. An outbreak of foxglove leaf poisoning
When the Heart Starts to Fail
The cardiac symptoms of foxglove poisoning are what turn a scary situation into a life-threatening one. Bradycardia, an abnormally slow heart rate, is among the most common findings. But the arrhythmias can take many forms: conduction blocks where electrical signals are delayed between the upper and lower chambers, premature beats originating from abnormal foci, and in severe cases, ventricular tachycardia, a rapid, disorganized rhythm that can degenerate into cardiac arrest.
The fatal case mentioned earlier shows how quickly the cardiac picture can deteriorate. The patient arrived with a heart rate of 54 beats per minute and a blood potassium level of 7.6 mEq/L, far above the normal range. Her ECG initially showed a first-degree atrioventricular block with premature atrial contractions, but within three hours of arrival, she developed polymorphic ventricular tachycardia, a rhythm that is immediately life-threatening.2PubMed. Fatal cardiac glycoside poisoning due to mistaking foxglove for comfrey The combination of high potassium and cardiac glycoside poisoning is particularly ominous because both conditions independently destabilize the heart, and together they are synergistic.
Not every poisoning reaches this extreme. The pattern depends heavily on how much glycoside was absorbed and how quickly the person receives treatment. Mild exposures may produce only bradycardia and brief rhythm disturbances that resolve with monitoring. Severe exposures can progress to complete heart block or ventricular fibrillation within hours.
Yellow Vision and Other Neurological Effects
Foxglove poisoning can produce a distinctive visual disturbance that has fascinated physicians for centuries. Xanthopsia, a yellow-tinted vision, is one of the hallmark neurological signs of cardiac glycoside toxicity. Other visual symptoms include chloropsia (a green tint), photopsias (flashing lights), sensitivity to light, and in some cases visual hallucinations, all of which may occur with or without reduced visual sharpness.6PubMed Central. Xanthopsia Due to Digoxin Toxicity as a Cause of Traffic Accidents: A Case Report Art historians have speculated that Vincent van Gogh’s intensely yellow-toned later paintings may reflect digitalis toxicity, since he was reportedly treated with foxglove preparations, though that theory remains debated.
These visual changes are not just curiosities. They are clinically significant warning signs. In patients taking pharmaceutical digoxin, visual disturbances can be the first clue that drug levels have crept into the toxic range. For someone who has unknowingly ingested foxglove, describing the world as looking yellow or seeing halos around lights should prompt immediate suspicion of plant poisoning. The mechanism involves the glycosides affecting the retinal cells and the visual processing pathways, disrupting color perception at a cellular level.
How Accidental Poisonings Happen
Most foxglove poisonings are accidental, and they follow a surprisingly consistent pattern: someone mistakes foxglove leaves for an edible plant. The most common culprit is comfrey (Symphytum officinale), a popular herbal remedy whose broad, fuzzy leaves look almost identical to foxglove leaves when neither plant is flowering.5PubMed. An outbreak of foxglove leaf poisoning Foxglove has also been confused with borage, another herb used in salads and teas.7PubMed Central. Of mixed vegetables and cardiac arrhythmias – Digitalis purpurea confused with Borago officinalis: A case series of accidental digitoxin intoxications
The risk is highest in spring and early summer, when foxglove grows as a rosette of basal leaves before sending up its distinctive flower stalk. Without the telltale bell-shaped purple flowers, even experienced gardeners and foragers have been fooled. In one outbreak, a batch of herbal tea sold commercially turned out to contain foxglove leaves instead of comfrey, poisoning nine people.5PubMed. An outbreak of foxglove leaf poisoning Children are at risk as well, since foxglove is widely planted as an ornamental and curious toddlers may chew on leaves or suck nectar from the flowers. The glycosides are present in every part of the plant, including the water in a vase holding cut foxglove stalks.
Intentional ingestion, while less common, also appears in the medical literature. The case of the woman who brewed an entire plant’s leaves into tea after purchasing it online highlights how easily the plant can be obtained and how its toxicity may not be fully appreciated by the person consuming it.1PubMed Central. A case of intoxication with tea made from Digitalis purpurea
What to Do in an Emergency
If you suspect someone has eaten any part of a foxglove plant, call emergency services or your regional poison control center immediately. Do not wait for symptoms to appear. The gap between ingestion and serious cardiac effects can be several hours, and that window is when medical intervention is most effective.
At the hospital, treatment begins with decontamination. If the person arrives within one to two hours of ingestion, activated charcoal can be given to bind the glycosides in the gut and reduce absorption. In some cases, repeated doses of activated charcoal are used because the glycosides recirculate between the liver and intestines.7PubMed Central. Of mixed vegetables and cardiac arrhythmias – Digitalis purpurea confused with Borago officinalis: A case series of accidental digitoxin intoxications Beyond decontamination, care is supportive: IV fluids, anti-nausea medications, continuous cardiac monitoring, and correction of electrolyte abnormalities, especially potassium.
For severe cases with life-threatening arrhythmias or dangerously high potassium, the specific antidote is digoxin-specific antibody fragments, commonly known by the brand name DigiFab or historically Digibind. These antibody fragments bind to the glycosides in the bloodstream and neutralize them. In pharmaceutical digoxin overdoses, these fragments are highly effective and can reverse cardiac toxicity within minutes. But foxglove poisoning is trickier. The plant contains a cocktail of glycosides, not just digoxin, and the antibody fragments do not bind all of them equally well.
Why the Antidote Does Not Always Work as Expected
This is where the evidence gets somewhat sobering. In one case of foxglove extract poisoning treated with digoxin-specific Fab fragments, the fragments produced a transient improvement in the patient’s ECG and clinical status, but did not shorten the overall course of the poisoning the way they typically do for pharmaceutical digoxin overdoses.8PubMed. Treatment of foxglove extract poisoning with digoxin-specific Fab fragments In the outbreak involving nine patients, 40 to 80 mg of digoxin-specific antibody was given to the most severely affected patients without any apparent effect.5PubMed. An outbreak of foxglove leaf poisoning
The reason lies in the chemistry. Foxglove’s primary glycoside is digitoxin, not digoxin. The two are structurally similar but not identical, and the antibody fragments were designed to target digoxin. They have some cross-reactivity with digitoxin, but it is incomplete. Additionally, digitoxin has a much longer half-life in the body than digoxin does. In the case of the woman who drank foxglove tea, her plasma half-life was estimated at 76 hours, reflecting digitoxin’s slow elimination.1PubMed Central. A case of intoxication with tea made from Digitalis purpurea That means the poison lingers in the body far longer than pharmaceutical digoxin would, and a single dose of antibody fragments may be insufficient to neutralize it all.
None of this means the antidote should be withheld. It remains a critical intervention for severe poisoning, and even transient improvement in cardiac rhythm can buy time. But clinicians treating foxglove ingestion need to be aware that the textbook response seen in digoxin overdoses may not materialize, and prolonged monitoring with repeat dosing of the antibody fragments may be necessary. In some of the documented cases, temporary cardiac pacing was used alongside the antibody therapy to maintain a viable heart rhythm.
Laboratory Clues and Diagnostic Challenges
One complication in diagnosing foxglove poisoning is that standard hospital assays measure digoxin, not digitoxin. Since the two compounds are structurally similar, commercial digoxin immunoassays will cross-react with digitoxin and other plant-derived glycosides, producing a positive result. But the numbers can be misleading. In the outbreak of nine patients, peak serum digoxin concentrations measured by immunoassay ranged from 4.4 ng/mL to a staggering 139.5 ng/mL.5PubMed. An outbreak of foxglove leaf poisoning A reading of 139.5 ng/mL for actual digoxin would be almost inconceivable; the assay was picking up the full spectrum of plant glycosides and reporting them in digoxin-equivalent units.
This matters because the usual clinical thresholds for digoxin toxicity do not map directly onto plant poisoning. A physician unfamiliar with this quirk might either underestimate the severity (because a modestly elevated “digoxin” level in a plant poisoning case actually represents a much larger total glycoside burden) or be baffled by an astronomically high number. The clinical picture, not the lab value, should drive treatment decisions. Hyperkalemia, bradycardia, conduction blocks, and the patient’s history of possible plant exposure are more reliable indicators of severity than the number on the immunoassay.
Acute Plant Poisoning Versus Chronic Drug Toxicity
Most digitalis poisonings that hospitals see are not from foxglove plants at all. They involve patients taking pharmaceutical digoxin for heart conditions who gradually accumulate too much drug in their system due to kidney problems, drug interactions, or dose miscalculation. Chronic digoxin toxicity actually makes up the majority of digitalis poisonings and can be harder to manage than acute ingestions.9PubMed Central. Chronic Digoxin Toxicity: An Evaluation of Digoxin-Specific Antibodies and Other Management Options
The distinction matters for treatment and prognosis. In acute poisoning from a plant, the gastrointestinal, neurological, and cardiac conduction systems are all hit hard and quickly. Disturbances to the heart’s signaling nodes and atrioventricular blocks are typical early findings. In chronic toxicity from pharmaceutical use, ventricular ectopy and various arrhythmias tend to predominate, while sinus node and AV block problems are present in both patterns.10PubMed. Acute and chronic digitalis toxicity: presentation and treatment For acute plant poisonings, the priority is clearing as much glycoside as possible from the gut before it absorbs, making early activated charcoal and timely hospital arrival especially critical.
William Withering and the Long Shadow of Foxglove in Medicine
Foxglove’s place in medicine goes back to the late 18th century, when the English physician William Withering learned of a folk remedy for “dropsy” (fluid buildup from heart failure) being dispensed by a local herbalist in Shropshire. Using his training as a botanist, Withering identified foxglove as the key ingredient in the herbalist’s recipe and spent years systematically testing it on patients. He documented its ability to strengthen the heartbeat in people with cardiac failure, but he also carefully cataloged the symptoms of overdose: nausea, disturbed vision, dangerously slow pulse.11PubMed. The foxglove, “The old woman from Shropshire” and William Withering
Withering’s work in 1785 essentially created the field of dose-finding for cardiac drugs, and the rules he laid out for prescribing foxglove infusions remained relevant for nearly two centuries. Pharmaceutical digoxin, derived from a related species (Digitalis lanata), became one of the most widely prescribed heart drugs in the 20th century. The irony is that despite centuries of medical use, the fundamental problem Withering identified never went away: the gap between a helpful dose and a harmful one remains perilously small. Modern pharmacology simply moved the uncertainty from “how many leaves” to “how many milligrams,” while the underlying biology stayed the same.