Too much caffeine: symptoms, what to do and when to get help

Key takeaways

• The FDA lists a faster heart rate, palpitations, high blood pressure, sleep problems, anxiety, jitters, upset stomach, nausea and headache as signs of too much caffeine.
• MedlinePlus adds restlessness, shakiness, dizziness, dehydration and dependency to the list.
• Overdose signs such as breathing trouble, confusion, seizures, vomiting or an irregular heartbeat need medical help right away.
• There is no single dose at which symptoms start: the FDA says people vary widely in how sensitive they are to caffeine.

Get help now if you have any of these symptoms

Some symptoms of too much caffeine are signs of an overdose. MedlinePlus lists breathing trouble, confusion, agitation or hallucinations, seizures, an irregular or rapid heartbeat, muscle twitching, vomiting and fever among the symptoms of a caffeine overdose in adults, and its advice is to seek medical help right away.

Call your local emergency number (911 in the US) if someone has these symptoms. In the US you can also call the national Poison Help line on 1-800-222-1222, which MedlinePlus describes as free, confidential and open 24 hours a day. MedlinePlus also says not to make the person throw up unless poison control or a health care provider tells you to.

The NHS adds that heart palpitations that do not go away, or that come with chest pain, shortness of breath, or feeling faint or fainting, need emergency care. Don’t wait to see whether these settle on their own.

• Trouble breathing or shortness of breath
• Confusion, hallucinations or a seizure
• Palpitations with chest pain, or with feeling faint or fainting
• A racing or irregular heartbeat that does not settle
• Vomiting

Common symptoms of too much caffeine, by body system

Health agencies list the same core symptoms. The FDA names an increased heart rate, heart palpitations, high blood pressure, insomnia or disrupted sleep, anxiety, jitters, an upset stomach, nausea and headache. MedlinePlus lists restlessness and shakiness, insomnia, headaches, dizziness, a fast heart rate, dehydration, anxiety and dependency, meaning you need more caffeine to get the same result.

The symptoms follow from what caffeine does in the body. MedlinePlus explains that caffeine stimulates the central nervous system, raises blood pressure and increases the release of acid in the stomach, which can lead to an upset stomach or heartburn. EFSA, the European food safety agency, says the short-term problems caffeine can cause in adults and children include interrupted sleep, anxiety and behavioural changes.

What to do right now if you had too much caffeine

If you have mild symptoms and none of the emergency signs above, the main step is simple: don’t have any more caffeine today. That includes tea, cola, energy drinks and chocolate as well as coffee, because MedlinePlus notes that caffeine occurs naturally in coffee beans, tea leaves, kola nuts and cacao.

Then give it time. MedlinePlus says caffeine reaches its peak level in the blood within an hour and that you may feel its effects for four to six hours. For what does and does not help, see our guide on whether you can flush caffeine out. For shakiness and a racing mind, our page on how to stop caffeine jitters has steps for the next hour.

If you feel dizzy, the NHS advice for dizziness is to lie down until it passes, then get up slowly, and to drink plenty of fluids, especially water. Our page on feeling dizzy after coffee covers this in more detail. The FDA advises talking with a health professional about your caffeine intake if you get any of its listed symptoms, and that is worth doing if they keep coming back.

How much caffeine causes symptoms?

There is no single number. For most adults, the FDA cites 400 mg a day as an amount not generally associated with negative effects, and EFSA says single doses up to 200 mg raise no safety concerns for healthy adults. But the FDA also says there is wide variation in how sensitive people are to caffeine and how fast they clear it, so some people get symptoms well below these amounts.

Dose still matters a lot. In a study of 102 adults who used little caffeine, 50 mg did not raise anxiety ratings, while 450 mg raised anxiety in most of them. At the extreme, the FDA estimates that toxic effects such as seizures can occur with rapid intake of around 1,200 mg, which is less than half a teaspoon of pure caffeine.

Cups are a poor guide. The FDA gives 113 to 247 mg for 12 ounces of brewed coffee and 41 to 246 mg for 12 ounces of an energy drink, and lab tests of the same coffee bought from the same shop on six days found 259 to 564 mg per serving. If you got symptoms from a drink that is usually fine, a stronger cup is one possible reason. Check our caffeine chart and the guide to how much caffeine is too much for daily limits by group.

Who should ask a doctor about limiting caffeine

MedlinePlus advises some people to check with a health care provider about limiting caffeine: those who are pregnant or breastfeeding, have sleep disorders, migraines or other chronic headaches, anxiety, reflux (GERD) or ulcers, an abnormal heart rhythm or high blood pressure, or take certain medicines or supplements, including stimulants, some antibiotics, asthma and heart medicines. For questions about a medicine, ask your doctor or pharmacist.

Children and teens should not have as much caffeine as adults, and MedlinePlus says children can be especially sensitive to it. The FDA notes that medical experts advise against energy drinks for children and teens because of their sugar and caffeine, and that too much caffeine in this group can cause a fast heart rate, palpitations, high blood pressure, anxiety, sleep problems, digestive problems and dehydration.

Too much caffeine or caffeine withdrawal?

Some symptoms appear on both lists, so timing helps tell them apart. Too much caffeine shows up within hours of a drink, around the time caffeine peaks in your blood. Withdrawal shows up when a regular user stops caffeine: a review of caffeine withdrawal studies found that symptoms typically start 12 to 24 hours after the last dose, peak at 20 to 51 hours and last two to nine days.

The withdrawal symptoms that review confirmed include headache, fatigue, low energy, drowsiness, low mood, difficulty concentrating and irritability. Headache and nausea can come from either cause. If you feel worse the day after stopping caffeine, see our guide to caffeine withdrawal rather than treating it as an overdose.

Common questions