Caffeine Overdose: Symptoms, Amounts and What to Do

If you have chest pain, an irregular heartbeat, trouble breathing, confusion or a seizure, or someone has swallowed caffeine powder or pills, stop reading and call: 1-844-POISON-X (1-844-764-7669) in Canada, 1-800-222-1222 in the United States, or emergency services. ^{[5] [2]}

For everyone else, here is where the line sits. The toxicology review that gathers the case reports puts the start of toxic symptoms near 1 g of caffeine in one sitting, hospital at around 2 g, and the fatal cases mostly at 5 g or more. You are a long way from any of those with a pot of coffee. Your 8 oz cup of brewed coffee is about 95 mg, so 1 g is more than ten cups at once and 5 g is more than fifty. The overdoses that reach a hospital come from pure powder, tablets and concentrates, and this page is mostly about keeping you well clear of those. ^{[1] [10]}

What are the symptoms of a caffeine overdose?

Your heart first, then your stomach, then your head. MedlinePlus lists what you may notice as an adult: trouble breathing, changes in alertness, agitation, confusion and hallucinations, seizures, diarrhea, dizziness, fever, increased thirst and urination, an irregular or rapid heartbeat, muscle twitching, nausea and vomiting, and trouble sleeping. It adds a line you should remember: the acute symptoms of caffeine poisoning and an acute anxiety attack can look very much alike, so if you are prone to panic, the caffeine may be what you are feeling. ^[2]

The useful way for you to read that list is in two tiers.

The first tier is what a fourth coffee does to you. In one study, a 500 mg dose was enough to raise tension, nervousness, nausea, tremor, sweating and palpitations in volunteers, so you do not need a gram to feel rough. The second tier is what the case reports describe at gram doses, and you will not mistake it for a bad coffee: heart rhythm disturbances of every kind, severe vomiting, muscle breakdown, and seizures. ^{[1] [3]}

How much caffeine is an overdose?

There is no single number, but the case literature gives you a ladder. Every bar is a dose at which harm has been seen, not a dose at which it starts for everyone. Your body weight, your heart and your medications move you up or down it.

Now put those in your hand. Your brewed coffee is about 95 mg a cup, a Monster is about 160 mg, a Red Bull is 80. ^{[10] [11] [12]}

The arithmetic is the point for you. You would have to drink more than fifty cups of coffee in one sitting to reach the fatal figures, and the review notes that doses up to 50 g have been survived with treatment while others died at 5 g untreated. If you ever see your blood level, the numbers run the same way: symptoms often begin above 15 mg per litre, 50 is called toxic, and 80 or more is treated as lethal, though people with existing heart conditions have come to harm below that. ^[1]

Coffee can still make you ill. The review's clearest coffee case is a 44 year old woman of about 40 kg who drank roughly a litre, an estimated 565 mg, and six hours later had nausea, vomiting, chest tightness, muscle twitching, palpitations and muscle breakdown. The authors point to her low body weight. If you are small, your ladder is shorter, and you reach each rung with fewer cups. ^[1]

Where do caffeine overdoses actually come from?

Powder, tablets and concentrates, bought in bulk, and probably not from your kitchen. The FDA's warning is specific: one teaspoon of pure powdered caffeine carries the caffeine of 28 cups of coffee, half a cup of a liquid concentrate more than 20 cups, and the products are sold in packages holding thousands of servings, so you are expected to measure a safe dose out of a lethal container with kitchen spoons that are not precise enough to do it. The FDA has taken action against bulk pure caffeine products and says some remain on sale. ^{[4] [3]}

Tablets are the other route, and if you keep them for study nights you should know this. The review notes that intentional overdoses typically involve caffeine tablets, and gives one natural experiment: Sweden cut the tablets allowed per box from 100 to 250 down to 30, and from 2007 to 2009 recorded no fatal caffeine intoxications. A separate 2018 analysis of the published caffeine-related deaths found 92 of them and flagged how easy the powders and tablets are to buy online. ^{[1] [6]}

Energy drinks sit in between for you. Canada caps a single-serve can at 180 mg and requires a caution label, so a can is a large coffee, not a hazard on its own; your trouble starts with cans on top of cans, or cans on top of pills. Our Monster page has the per-can figures. ^[8]

What should you do if you have had too much caffeine?

Judge your tier, then act.

If it is a few cups too many. Stop. Do not take anything else with caffeine in it, including tea, cola or a chocolate bar. Sit down, eat something if your stomach allows, drink water, and wait. Caffeine leaves on a half-life of about five hours, so the worst of it eases within a couple of hours and most of it is gone by the next day; our half-life page has the curve. Nothing you can drink speeds that up. If you are shaking and your heart is racing, that is the caffeine, and it passes.

If it is an emergency. Chest pain, an irregular heartbeat, trouble breathing, confusion, repeated vomiting or a seizure, or any swallowed powder, tablets or concentrate, in anyone: call. In Canada the poison centres share one number, 1-844-POISON-X (1-844-764-7669), free, confidential and open 24 hours; you do not need to be sure it is an emergency to call. In the United States it is 1-800-222-1222 or poisonhelp.org. Have ready the person's age, weight and condition, the product and its strength, how much and when. Do not make anyone vomit unless the poison centre or a clinician tells you to. ^{[5] [2]}

At the hospital, you can expect monitoring of pulse, breathing and blood pressure, an ECG, blood and urine tests, and treatment that may include activated charcoal, intravenous fluids, medicine for symptoms and, for dangerous rhythms, a shock to the heart. The review adds that there is no standard regimen: a mild 1 g case with restlessness and palpitations may simply be watched, perhaps with a sedative, while massive doses have been treated with dialysis to pull caffeine out of the blood. Bring the container with you. ^{[2] [1]}

Who is at higher risk?

• If you are small. Doses are per kilogram, and the coffee case above was a 40 kg woman. At 55 kg you reach every line on the ladder sooner than someone at 90 kg.
• If you have a heart condition. The review reports serious toxicity and deaths below the usual lethal blood level in people with existing cardiovascular disease, so your margin is smaller than the ladder shows.
• If you are a teenager. The FDA says too much caffeine in children and teens may cause a fast heart, palpitations, high blood pressure and anxiety, and Health Canada's limit under 18 is 2.5 mg per kg a day. The daily limits page has the table.
• If you are pregnant. The ceilings are lower, 200 to 300 mg a day depending on the authority, and the pregnancy page explains why.
• If you take something that slows clearance. Some medications and late pregnancy lengthen caffeine's half-life, so the same dose stays with you longer and stacks with your next one.

What to do

• Jittery after too much coffee? Stop, eat, drink water, wait. It passes on a five-hour half-life and you will be fine by morning.
• Chest pain, irregular heartbeat, confusion, seizure? Call 1-844-POISON-X in Canada or 1-800-222-1222 in the United States, or emergency services. Do not induce vomiting.
• Anyone swallowed caffeine powder or pills? Treat it as an emergency regardless of how they look. A teaspoon of powder is 28 cups.
• Keep pure caffeine out of your house. The FDA says the gap between a safe and a lethal spoonful is too small for you to measure in a kitchen.
• Counting toward a limit rather than an overdose? Our how much caffeine is too much page has the 400 mg day and who needs less.

The short version

Toxic symptoms begin near 1 g of caffeine in one sitting, around 2 g has meant hospital, and most deaths involved 5 g or more, which is more than fifty cups of coffee at once. The signs you would notice are a racing or irregular heart, tremor, vomiting, agitation and, at the severe end, seizures. Coffee can make you ill; powder, tablets and concentrates are what kill, so keep them out of your house. If it is an emergency, call 1-844-POISON-X in Canada or 1-800-222-1222 in the United States, and do not make anyone vomit unless they tell you to.