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How much coffee can a healthy adult drink before it starts to affect them in a bad way?

For example, some friends of mine get headaches if they drink more than 2 cups in a single day.

  • 2
    Can you elaborate on what negative effects you want to avert? For example, if you want to avoid iron deficiency, it's not so important how much coffee to drink, but when to drink it, i.e. you should not drink coffee during or after meals. – Turion Apr 4 '15 at 10:14
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    @Turion, My gosh, I do that all the time. How many minutes must we wait? – Pacerier Jun 3 '15 at 21:16
  • @Pacerier, I don't know a specific time. Basically, coffee and iron-rich meal shouldn't meet in the intestine. – Turion Jun 4 '15 at 8:02
  • Unless you're okay with dependancy/addiction & withdrawal, I recommend no more than a cup or two a WEEK, see more info here: health.stackexchange.com/a/16996/809 – Jonathan Jul 27 '18 at 18:34
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There are many factors in determining how much coffee one can drink in a day. Caffeine metabolism1 is a big one. People who metabolize caffeine slow, probably shouldn't have more than 100mg of caffeine (about a cup) a day. Fast metabolizers of caffeine can usually have between 400-500mg (about 5 cups) a day.2 For the general population, 400mg (about 4 cups) should be the limit. Going over this may cause several side effects such as insomnia, restlessness, headaches, and upset stomach.3 It usually isn't very hard to know your limit of drinking coffee. If coffee has a strong effect on you right away, drink less coffee, or consider drinking tea. If coffee has a weak effect on you, then you can drink more. Most people will fall somewhere in between.


[1] Why do I feel shaky after only a small amount of caffeine?

[2] Caffeine Consumption

[3] Caffeine: How much is too much?

  • Interestingly, it would be 100+ cups in less than 24 hours to kill you: huffingtonpost.com/2014/08/28/… – Tim Apr 12 '15 at 20:11
  • @Tim Hmm, interesting. But you will start hallucinating before you reach that point :P – michaelpri Apr 12 '15 at 20:15
  • Yes, and probably pass out before, so I wouldn't advise trying to get anywhere near that! – Tim Apr 12 '15 at 20:16
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    michaelpri, as a side note, if you include links to reference material, you should indicate where those links go (footnotes or inline references) so folks don't have to click through to unknown sources/sites blindly. – Robert Cartaino Apr 15 '15 at 16:45
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    I actually really like this reference style. It's similar to the one I typically use, but easier to do, and more informative. I started a discussion on meta a while ago about standards in references, and I think this style makes a great example of good standards. – TheEnvironmentalist May 22 '15 at 9:48
5

It really depends on the coffee which its caffeine content (its main psychoactive substance) can vary by size, bean origin, roast method and other factors.

Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two "energy shot" drinks. Although caffeine use may be safe for adults, it's not a good idea for children. See: Caffeine: How much is too much? at Mayo Clinic

Higher consumption of 1000–1500 mg per day is associated with a condition known as caffeinism.


Caffeinated beverages like coffee and soft drinks give short bursts of energy, but can actually cause fluid loss. Caffeine has been shown to temporarily raise blood pressure, and reduces blood flow to inactive limbs.

Like many drugs, caffeine is chemically addictive and recent publication of Diagnostic and Statistical Manual of Mental Disorders (DSM), caffeine withdrawal was finally included as a mental disorder for the first time.

Soon after you drink coffee (containing caffeine), it’s absorbed through the small intestine and dissolved into the bloodstream and it’s able to penetrate the blood-brain barrier and enter the brain.

Regular ingestion of the drug (i.e. coffee/tea, soda or energy drinks) alters your brain’s chemistry and physical characteristics actually change over time, leading to fatigue, headaches and nausea if you try to quit. However, compared to many drug addictions, the effects are relatively short-term.

Few quotes from Daily Mail:

Large amounts of caffeine can cause heart palpitations, fits and even death, as well as raising the risk of Type 2 diabetes.

Heavy consumption has also been linked to a greater risk of depression, addiction and alcohol dependency.

Energy drinks could be more likely to cause a caffeine overdose because they can be drunk quickly, unlike hot drinks like tea or coffee, the Energy Drink Consumption in Europe study said.

Several deaths worldwide have been linked to excessive consumption of energy drinks, although scientists say more research is needed to prove a link.

Recommended maximum caffeine intake is about 400mg per day – equivalent to around five cups of filter coffee.

'Reproductive-aged women (⩽ 300 mg caffeine per day) and children are ‘at risk’ subgroups who may require specific advice on moderating their caffeine intake', study said.

On Live Science we can read:

Coffee drinking could lead to a mental disorder. If you experience five or more symptoms, such as red face, nervousness and restlessness, during or right after your cup of Joe, you may be diagnosed with coffee intoxication.

According to a new edition of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-5), excessive caffeine intake can lead to a condition known as “caffeine intoxication,”.

In other words, caffeine withdrawal is now a recognized disorder, and is listed in the DSM-5.

Caffeine is a drug, a mild stimulant, which is used by almost everybody on a daily basis,” said Dr. Charles O’Brien, who chairs the Substance-Related Disorder Work Group for DSM-5 (via New York Post). “But it does have a letdown afterwards. If you drink a lot of coffee, at least two or three [236 ml] cups at a time, there will be a rebound or withdrawal effect.”

Here are top 10 caffeine withdrawal symptoms:

  1. Headache
  2. Sleepiness
  3. Irritability
  4. Lethargy
  5. Constipation
  6. Depression
  7. Muscle Pain/Stiffness
  8. Lack of Concentration
  9. Flu-like symptoms
  10. Insomnia

In rare cases when consumed at high enough doses, caffeine can kill.

caffeine curve


Related:

  • 2
    Wikipedia and the Daily Mail (a tabloid) are really not good sources – Zaralynda Apr 13 '15 at 2:54
  • @Zaralynda, agree on Daily Mail, but Wikipedia is an excellent source. – Turion Apr 13 '15 at 17:13
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    @Turion Wikipedia is only as good as its sources and if we want people to think more critically here, they should be using primary sources more – Zaralynda Apr 13 '15 at 17:40
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    Related meta post: Is Wikipedia a reliable source? – kenorb Apr 17 '15 at 11:19
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    Study cited by Daily Mail. I found it by googling one of the quotes that the article used ("As energy drink sales are rarely regulated by age and there is a proven negative effect of caffeine on children, there is the potential for a significant public health problem in future."). If you want to source from a popular site for readability, I prefer something like Science Daily; their articles are traceable to the study they are based on – Zaralynda Apr 26 '15 at 19:01
3

While this is not a complete answer, I'm pointing out here that coffee intake is adverse to iron absorption. Caffeine does play a role here, although I don't know to what extent other substances in coffee do. I have asked a separate question here.

For this reason, it is recommended not to drink coffee together with, or directly after iron-rich meals (say, a breakfast with oatmeal and fruits) since the intake and the benefits of the iron would be inhibited. This applies especially to people who have low haemoglobin levels, but also to healthy adults who want to keep their iron levels up. Pregnant women should be especially careful and best avoid coffee completely since coffee consumption is linked to iron deficiency anemia in their infants.

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I recently read a fantastic article in the first issue of National Geographic Science. To sum it up for you, coffee is actually great for you. 3 cups a day can decrease mortality by 12%. Right now I do not have the magazine on me but here is a shorter version. My only concern is caffeine.

  • This answer seems incomplete to me. You say that your only concern is caffeine. What would be your concerns and what scientific research is available to support your claim in relation to the OP question? – Chris Rogers Mar 26 '18 at 12:35
  • This is also not an answer to the question. While it may be true that 3 cups can be beneficial, the question is how much is harmful. Please read the help section on how to answer questions, and how to reference. – JohnP Mar 26 '18 at 14:25

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