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Short answer: For most healthy adults, up to 400 mg of caffeine a day is not generally linked to harmful effects, according to the FDA and Health Canada. That is roughly four 8-ounce cups of brewed coffee. Europe's food safety authority adds that single doses up to about 200 mg are not a concern for healthy adults. Too much caffeine can cause jitters, a racing heart, anxiety, an upset stomach and poor sleep, and very large amounts taken quickly, about 1,200 mg, can cause seizures. Some people feel these effects at much lower doses.
Caffeine is the most widely used stimulant in the world, and most people never come close to a dangerous amount. But the line between "enough" and "too much" depends on how much you have, how fast, and how your body handles it. Here is the daily limit health authorities use, what 400 mg looks like in real drinks, the signs you've had too much, when caffeine becomes dangerous, and who should have less.
What you'll learn
- The daily caffeine limit for healthy adults, and what 400 mg looks like
- Signs you've had too much caffeine
- When caffeine becomes dangerous, and what to do
- Who should have less, and how to cut back
How much caffeine is too much in a day?
For most healthy adults, the FDA cites up to 400 mg a day, about two to three 12-ounce cups of coffee, as an amount not generally associated with negative effects (FDA). Health Canada sets the same recommended maximum of 400 mg a day for adults (Health Canada), and the European Food Safety Authority found intakes up to 400 mg a day, spread through the day, raise no safety concerns for healthy adults other than pregnant women (EFSA).
How fast you have it matters too. EFSA found single doses up to 200 mg, about 3 mg per kilogram of body weight, raise no safety concerns for healthy adults, and noted that even 100 mg close to bedtime may affect sleep in some people (EFSA). And people vary widely in how sensitive they are to caffeine and how fast they break it down (FDA), so 400 mg is an upper limit, not a target.
What does 400 mg of caffeine look like?
Approximate caffeine per serving and how many servings add up to 400 mg, from USDA FoodData Central unless noted:
| Drink | Serving | Caffeine | Servings to reach 400 mg |
|---|---|---|---|
| Brewed coffee | 8 fl oz | 95 mg | about 4 |
| Espresso | 1 shot (1 fl oz) | 63 mg | about 6 |
| Instant coffee | 6 fl oz | 46 mg | about 9 |
| Black tea, brewed | 8 fl oz | 47 mg | about 9 |
| Green tea, brewed | 8 fl oz | 29 mg | about 14 |
| Matcha | Made with 2 g of powder | 28 to 70 mg (Meyer et al., 2023) | about 6 to 14 |
| NeuroCoffee mushroom coffee | 2 tbsp | 30 mg | about 13 |
| NeuroMatcha | 2 tbsp | 17.64 mg | about 23 |
| Energy drinks | 16 fl oz | 54 to 328 mg (FDA) | about 1 to 7 |
Coffee-shop drinks can be much stronger than these averages. The FDA lists 113 to 247 mg in a 12-ounce brewed coffee (FDA), and when researchers bought the same 16-ounce coffee from the same shop on six different days, it contained anywhere from 259 to 564 mg (McCusker et al., 2003). In other words, one large coffee can come close to, or pass, a full day's limit. Energy drink labels may not show the actual amount of caffeine (MedlinePlus). For more, see how much caffeine is in coffee and how much caffeine is in tea.
Signs you've had too much caffeine
The FDA lists these as signs you may be having more caffeine than you can handle (FDA):
- Increased heart rate or heart palpitations
- High blood pressure
- Insomnia or sleep disruptions
- Anxiety
- Jitters
- Upset stomach or nausea
- Headache
Health Canada also lists irritability and nervousness (Health Canada), and MedlinePlus adds restlessness, shakiness and dizziness (MedlinePlus). These effects usually fade as the caffeine wears off; its effects typically last 4 to 6 hours (MedlinePlus), and the average adult clears half of it in about 5 hours (StatPearls). For quick ways to feel steadier, see how to get rid of caffeine jitters.
Caffeine overdose: how much is dangerous?
Toxic effects such as seizures can occur with rapid consumption of about 1,200 mg of caffeine (FDA). That is hard to reach with coffee or tea, but much easier with pure or highly concentrated caffeine products.
The FDA warns that one teaspoon of pure powdered caffeine can contain as much caffeine as about 28 cups of coffee, that the difference between a safe and a toxic amount in these products is very small, and that they have contributed to at least two deaths in the United States (FDA). Avoid pure caffeine powders and liquid concentrates, and be careful with energy shots and stacking several caffeinated products.
Get help right away for signs of a caffeine overdose such as trouble breathing, confusion, seizures, a fast or irregular heartbeat, or vomiting (MedlinePlus; FDA). Call 911 in an emergency, or call Poison Control at 1-800-222-1222 in the United States (MedlinePlus).
What to do if you've had too much caffeine
- Stop having caffeine for the rest of the day, including tea, soda, energy drinks, chocolate and pre-workout products.
- Give it time. There is no quick way to clear caffeine. Your liver breaks it down, and the average adult clears half of it in about 5 hours (StatPearls).
- Drink water and eat something light if your stomach feels unsettled.
- Watch for warning signs. Trouble breathing, a fast or irregular heartbeat, confusion, vomiting or a seizure need urgent medical care (MedlinePlus).
For how long caffeine lasts, see how long caffeine stays in your system.
Who should have less caffeine?
People who are sensitive to caffeine, have sleep problems, a heart condition, high blood pressure or anxiety, are pregnant or breastfeeding, or take certain medications may need less.
- People who are sensitive to caffeine. If you feel jittery, anxious or can't sleep, consider lowering your intake or avoiding caffeine (Health Canada).
- People with sleep problems. Research suggests finishing a typical cup of coffee (about 107 mg) at least 8.8 hours before bed (Gardiner et al., 2023).
- People with heart conditions, high blood pressure or anxiety. Ask your health care provider how much is right for you. See also does caffeine raise blood pressure?
- People who are pregnant, trying to get pregnant or breastfeeding. The FDA advises talking with your health care provider about caffeine (FDA).
- People taking certain medications. Some drugs, including fluvoxamine and some antibiotics, slow how fast your body clears caffeine, and oral contraceptives can slow it too (Grzegorzewski et al., 2021). Ask your pharmacist.
This article is about adults. Talk to a pediatrician about caffeine for children and teens.
How to cut back on caffeine
If you want to have less, the FDA advises cutting back gradually; caffeine withdrawal is not considered dangerous, but it can be unpleasant (FDA). Swap one drink a day for a smaller size, half-caf or decaf, or a lower-caffeine option like green tea, and avoid caffeine late in the day. Keep in mind that decaf is not completely caffeine-free: an 8-ounce cup typically has 2 to 15 mg (FDA). For more, see caffeine withdrawal and coffee alternatives.
Common myths (quick reality check)
Myth: 400 mg a day is a goal to aim for. Reality: It is an upper limit for healthy adults, not a target. Many people feel side effects at lower amounts, and some groups should have less.
Myth: You can only get too much caffeine from coffee. Reality: Caffeine also comes from tea, soda, energy drinks, pre-workout products, chocolate and some medicines. Pure caffeine powders are especially risky.
Myth: A cold shower, exercise or extra water will flush caffeine out faster. Reality: Caffeine is cleared almost entirely by your liver, at its own pace: about half every 5 hours for the average adult. Time is the only reliable fix.
Myth: Decaf has no caffeine. Reality: Decaf has much less, typically 2 to 15 mg per 8-ounce cup, but not zero.
Frequently asked questions (FAQ)
How much caffeine is too much?
For most healthy adults, more than 400 mg a day is more than health authorities consider safe, and single doses over about 200 mg may be too much at once. Some people feel side effects at much lower amounts.
How many cups of coffee is too much?
About four 8-ounce cups of brewed coffee add up to 400 mg. A single large coffee-shop coffee can have more than 250 mg, so it is easy to go over.
What are the signs of too much caffeine?
A fast heart rate or palpitations, higher blood pressure, trouble sleeping, anxiety, jitters, an upset stomach or nausea, and headache.
How much caffeine can kill you?
Toxic effects such as seizures can occur with rapid consumption of about 1,200 mg. Pure and highly concentrated caffeine products are the main danger: one teaspoon of caffeine powder can equal about 28 cups of coffee. Get emergency help for symptoms of an overdose.
How long do the effects of too much caffeine last?
Caffeine's effects typically last 4 to 6 hours, and the average adult clears half of it in about 5 hours, so symptoms usually ease within a few hours.
Is 200 mg of caffeine a lot?
For a healthy adult, a single dose up to about 200 mg is not considered a safety concern, but it is about two cups of coffee at once and can cause jitters or affect sleep in sensitive people.
Related guides
- is caffeine a drug
- Caffeine in soda: Coke, Pepsi, Sprite, Dr Pepper and more
- How much caffeine is in a shot of espresso? Single, double and decaf
- Brain fog: symptoms, causes and what helps
- How much caffeine is in a cup of coffee?
- How much caffeine is in tea?
- How long does caffeine stay in your system?
- How to get rid of caffeine jitters
- Caffeine withdrawal
- Does caffeine raise blood pressure?
Disclaimer and when to seek help
This article is for general education and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. Call 911 or Poison Control (1-800-222-1222) for signs of a caffeine overdose. Talk to your health care provider about caffeine if you are pregnant or breastfeeding, have a heart condition, high blood pressure, anxiety or sleep problems, or take medication.
References
- U.S. Food and Drug Administration. "Spilling the Beans: How Much Caffeine Is Too Much?"
- U.S. Food and Drug Administration. "Pure and Highly Concentrated Caffeine."
- Health Canada. "Caffeine in Foods."
- European Food Safety Authority. "Caffeine" (Scientific Opinion on the safety of caffeine, 2015).
- U.S. Department of Agriculture. FoodData Central (SR Legacy: coffee, brewed; espresso; instant coffee; tea, black and green, brewed).
- McCusker RR, Goldberger BA, Cone EJ. "Caffeine content of specialty coffees." Journal of Analytical Toxicology, 2003;27(7):520-522. doi:10.1093/jat/27.7.520
- Meyer BR, et al. "Catechin composition, phenolic content, and antioxidant properties of commercially-available bagged, gunpowder, and matcha green teas." Plant Foods for Human Nutrition, 2023;78(4):662-669. doi:10.1007/s11130-023-01121-2
- MedlinePlus (U.S. National Library of Medicine). "Caffeine".
- MedlinePlus (U.S. National Library of Medicine). "Caffeine overdose".
- Evans J, Richards JR, Battisti AS. "Caffeine." In: StatPearls. StatPearls Publishing; last update May 29, 2024. NCBI Bookshelf NBK519490
- Grzegorzewski J, et al. "Pharmacokinetics of Caffeine: A Systematic Analysis of Reported Data for Application in Metabolic Phenotyping and Liver Function Testing." Frontiers in Pharmacology, 2021;12:752826. doi:10.3389/fphar.2021.752826
- Gardiner C, et al. "The effect of caffeine on subsequent sleep: A systematic review and meta-analysis." Sleep Medicine Reviews, 2023;69:101764. doi:10.1016/j.smrv.2023.101764
- OurJrney Product Facts: NeuroCoffee (30 mg caffeine per 2-tablespoon serving) and NeuroMatcha (17.64 mg caffeine per 2-tablespoon serving).
