For most adults, an oral dose of about 5 to 10 grams of caffeine, roughly 100 to 200 milligrams per kilogram of body weight, can be lethal. Severe toxicity can start at around 1 to 2 grams, and risk rises with rapid intake of concentrated forms like pure powder. By contrast, healthy adults can generally consume up to about 400 milligrams per day without safety concerns, according to European regulators.
What is a lethal dose of caffeine?
The best available synthesis of case reports finds that lethal outcomes usually occur after multi-gram exposures, with wide individual variability. In the largest review to date of 216 published cases, the median reported intoxication dose was 12 grams, and doses in the 5 to 10 gram range were considered potentially lethal. Blood levels above about 80 mg/L are also viewed as potentially fatal, while symptoms can begin at roughly 15 mg/L.
Doses of 5 to 10 grams of caffeine can be lethal, and intoxication symptoms may start at about 1 to 2 grams or serum levels above 15 mg/L (case-report review, 1883–2023).
Because sensitivity varies with body weight, genetics, medications, liver function, and pregnancy, clinicians often frame risk per kilogram. A useful rule of thumb from toxicology case literature is that around 100 to 200 mg/kg by mouth can be fatal, though survival has occurred above that with aggressive care and some deaths have occurred below it in vulnerable individuals.
How does caffeine overdose cause harm?
At common doses, caffeine mainly blocks adenosine receptors, increasing alertness. At very high levels, additional mechanisms emerge: excess catecholamine release, beta-adrenergic stimulation, and phosphodiesterase inhibition. These drive dangerous effects on the heart and nervous system.
The large case review reports frequent findings of tachycardia, vomiting, agitation and tremor early, progressing to metabolic acidosis, hypokalemia, seizures, and malignant arrhythmias such as wide-complex tachycardia and ventricular fibrillation in severe cases. Deaths are most often due to refractory arrhythmia or cardiocirculatory failure.
What are the symptoms of caffeine intoxication?
- Early and common: nausea and recurrent vomiting, palpitations, tremor, anxiety, agitation, rapid breathing
- Laboratory changes: metabolic acidosis, elevated lactate, low potassium, sometimes hyperglycemia or rhabdomyolysis
- Severe complications: seizures, wide-complex tachycardia, ventricular fibrillation, pulseless electrical activity
In the 89 cases with detailed presentations in the review, tachycardia occurred in 87, vomiting in 60, and seizures in 15. Seizures and wide-complex tachycardias were associated with worse outcomes.
How much caffeine is safe to consume daily?
The European Food Safety Authority’s 2015 safety assessment concluded that up to 400 mg per day is harmless for healthy adults, up to 200 mg per day for pregnant and breastfeeding women, and less than 2.5 mg/kg for children and adolescents. These values reflect total daily intake from all sources.
EFSA: up to 400 mg/day for healthy adults and 200 mg/day in pregnancy and breastfeeding are considered safe (EFSA explains caffeine, 2015).
Typical amounts for context:
- Brewed coffee, 250 mL: about 80 to 100 mg
- Energy drink, 250 mL: about 80 mg, but some large servings approach 300 to 400 mg
- Tea, 250 mL: about 30 to 50 mg
- Cola, 355 mL: about 30 to 40 mg
- Caffeine tablet: commonly 100 to 200 mg per pill
Content varies by product and preparation. Always check labels and serving sizes.
Why are pure caffeine powders and concentrates especially dangerous?
Bulk powders and highly concentrated liquids can deliver gram-level doses quickly and are easy to mismeasure without laboratory-grade scales. The U.S. Food and Drug Administration has warned consumers and issued guidance that dietary supplements with highly concentrated or pure caffeine are unlawful and unsafe because small measurement errors can be fatal. See the FDA’s guidance for details on enforcement and risks (FDA guidance on highly concentrated caffeine).
In 2015, a UK university study miscalculated a dose and gave two students about 30 grams of caffeine instead of 0.3 grams; both required emergency dialysis and the university was fined £400,000 (case summary).
Even modest-seeming teaspoons of powder can equal dozens of cups of coffee. Liquids marketed as “energy” or “pre-workout” may also combine caffeine with other stimulants, which can compound risk.
What should you do if you suspect a caffeine overdose?
- Stop intake immediately and seek medical care if severe symptoms occur, such as chest pain, persistent vomiting, confusion, seizures, or a very fast or irregular heartbeat.
- In the United States, call Poison Help at 1-800-222-1222 for real-time guidance (poisonhelp.org). Contact your national poison center if you are outside the U.S.
- Do not try to “sleep it off” if symptoms are escalating. Do not induce vomiting unless instructed by a professional.
In hospital, clinicians may give activated charcoal soon after ingestion to reduce absorption, treat arrhythmias and seizures symptomatically, correct electrolyte disturbances, and, in severe cases, remove caffeine using blood-cleansing techniques such as hemodialysis. The case-review data suggest dialysis can improve survival even after very high exposures (review).