How much caffeine is too much?

How much caffeine is too much?

Caffeine is a drug, so like any drug there must be a limit. But just how many cups of coffee does it take to compromise your health? 

When we talk about drugs we generally think of either illegal drugs or pharmaceuticals. The term “drug,” however refers to all substances that have a physiological effect when introduced to the body, including caffeine. In fact, caffeine is probably one of the most frequently-ingested pharmacologically active substance in the world [1]. It’s everywhere—in coffee, tea, soft drinks, chocolate, prescriptions, and over-the-counter medicines.



Can you overdose on caffeine?

pouring coffee in a mug

Yes, although it’s rare. Lethal doses of caffeine have occured after ingestion of 10 grams or more, usually from intentional ingestion of medication. Caffeine overdoses from energy drinks have occurred as well, but lethal levels of caffeine are generally not seen with ingestion of coffee or tea due to the excessive amounts of fluid you would need to drink (we’re talking over 100 espresso shots) [3]. However, in children, levels such as 1 gram of caffeine (12 energy drinks in a row) can produce the symptoms of caffeine overdose [4]. 

Symptoms of caffeine overdose usually include tremors, nausea, vomiting, irregular heart rate, and confusion [4]. If you’re experiencing any of these, talk to your doctors. (But if your coffee jitters are only moderate, try getting back to an even keel with Hydrant.)



So how much caffeine can I have? 

Despite some disagreement between scientific studies on how exactly caffeine affects your health, there is a level of consensus on how you can drink whilst still keeping risk to health low. Consuming under 400 mg a day is thought to have no effect on factors such as heart health, behavior, reproductive health, etc [1, 2, 5]. This value is lower for pregnant women at 300 mg per day, as caffeine can affect both mother and child [1].

cups of coffee

It’s important to remember that guidelines are not generally a one-size-fits-all solution. In fact, the recommendation of 400 mg per day is calculated from a guideline of 6 mg per day for each kg a person weighs—so for an average 65 kg person, this works out to approximately 400 mg per day. Beyond weight, factors such as sex, age, smoking, or use of oral contraceptives can affect how we process caffeine [1].



What does 400 mg of caffeine a day mean? 

There is a large variation on the exact caffeine content across various brands and products, so be sure to carefully read the labels on the drinks you consume. Here’s a rough guide on how much caffeine you consume daily:


Food/drink item


Caffeine content

Minimum number to reach 400 mg

Filter coffee [6]

8 oz / 240 ml

75-85 mg

Just under 5 cups

Espresso shot [6]

1 oz / 30 ml

75-85 mg

Just under 5 shots

Brewed black tea [7]

8 oz / 240 ml

47 mg

8 and a half cups

Classic coca cola can [8]

12 oz / 330 ml

32 mg

12 and a half cans

Diet coca cola can [8]

12 oz / 330 ml

42 mg

9 and a half cans

Red bull can [9]

8.4 oz / 250 ml

80 mg

5 cans

Dark chocolate bar [10]

5.7 oz / 162 g

70 mg

Just under 6 bars

Even decaffeinated teas and coffees can contain a few mg of caffeine per cup [11]. Caffeine can also be present in prescription and non-prescription medicines.



How exactly does caffeine affect the body?

When caffeine is ingested, it is readily taken up by the gut, reaching maximum concentration in your blood around 1-1.5 hours after ingestion [1]. This caffeine then merrily spreads around your body, including into the brain, across a placenta, into breast milk, and even into semen [1]. Once in your body, caffeine can bind to receptors on the surfaces of your cells, and so preventing the chemicals the body naturally produces binding to these receptors. Caffeine doesn’t leave too easily either—the half life (time taken for the level of a substance in the body to drop by 50%) can vary between 3-7 hours [1].

One of the most famed effects of caffeine is its ability to keep you awake. Caffeine can prolong the onset of sleep, reduce total sleep time, effect sleep efficiency, and even worsen perceived sleep quality. Interestingly, these abilities of caffeine vary between individuals and their genetics [2].  

The scientific evidence on the long-term consequences of caffeine consumption on health can be conflicting. This evidence generally involves either correlating caffeine consumption and health outcomes in large populations or giving individuals controlled amounts of caffeine in a lab and observing changes in the body.

a lady and a cup of coffee during the day

For example take the effect of high caffeine intake on heart health. There is some evidence coffee consumption could increase blood cholesterol. However, studies on whether caffeine effects blood pressure disagree. Overall, the data is insufficient in drawing solid conclusions on how lots of caffeine might affect your heart [1]. Another example of inconclusive data is in studies relating caffeine and mood. The best evidence for caffeine increasing anxiety is in studies with adults who already have pre-existing anxiety disorders, so a definitive conclusion about caffeine and stress is hard to make [1].

Some of the strongest evidence for the negative effects of caffeine consumption surrounds the relationship between caffeine and pregnancy. As mentioned, caffeine can readily cross the placenta and thus be taken up by fetuses and affect their development. In addition to this, the half life of caffeine is markedly increased in fetuses. Caffeine has also been negatively associated with the ability to both get pregnant and keep a pregnancy [1]. Thus, pregnant women are generally advised to reduce caffeine intake.



What about taurine?

Taurine is an amino acid that your body can make itself. It’s abundant in the human brain, eye, heart, and reproductive organs. We also consume taurine in our diet in meat and seafood. Taurine can also be given to people with diagnosed taurine deficiencies and is now included in baby formulas. In addition, this amino acid is thought to have anti-oxidant and anti-inflammatory properties [12].

canned drinks

So taurine sounds like a good deal. Therefore, perhaps it’s not surprising that some energy drinks now include taurine and advertise it as playing a role in improving cognitive and physical performance. However, these claims are more wishful thinking than they are evidence-supported claims. There have been few human studies that examine whether or not taurine does as is claimed in the absence of other substances such caffeine and glucose. A couple of studies that did look at physical performance after taurine ingestion didn’t actually find any improvements [12]. This is a fairly new area of research, but currently the evidence just isn’t really there to draw hard conclusions.



Caffeine – everything in moderation 

Generally diet and health research doesn’t give black and white answers about what you should and shouldn't consume. However, basic guidelines can be made based on the available data. Yes, you can have too much caffeine, but consumption below 400 mg per day seems to have little adverse effects. Caffeinate responsibly!

Trying to cut down on caffeine? Going cold turkey can be hard. Try substituting just one of your daily cups of coffee with Hydrant. This simple electrolyte mix will help you retain focus, without all the coffee jitters.

Writer: Josie Elliott
Editor: Elizabeth Trelstad,



[1] P Nawrot et al, “Effects of caffeine on human health”, 2003, Food Additives and Contaminants Journal. A comprehensive review of evidence on how caffeine affects the body.
[2] I Clark and H Landolt, “Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials”, 2017, Sleep Medicine Reviews. A research article summarizing current evidence on how caffeine affects sleep.
[3] A Murray and J Traylor, “Caffeine toxicity”, last update 2018, NCBI bookshelf. A description of the effects of excess caffeine. 
[4] Alcohol and Drug Foundation, “Caffeine”, last updates Nov 2018. A great summary on the effects and use of caffeine as a drug.
[5] NHS “Four cups of coffee ‘not bad for health’ suggests review”, April 2017. A very accessible article explaining the research on caffeine and health.
[6] Starbucks, “Winter FY19 Starbucks Beverage Nutrition Information”. Starbucks gives the caffeine content of all sizes of all their beverages. This is a great resources for assessing and comparing the caffeine levels in commercial drinks.
[7] United States Department of Agriculture, National Nutrient Database – Beverages, tea, black brewed, prepared with tap water, April 2018The USDA details the nutritional content of thousands of food and drink products. 
[8] Coca-Cola, “The caffeine in your can”, Journey Staff. - A review of caffeine levels in common drinks, compared to a can of Coca-Cola.
[9] Red bull Q&A, “Can you drink too much of Red Bull Energy Drink”. Red Bull’s official answer to caffeine overdose inquiries. 
[10] United States Department of Agriculture, National Nutrient Database – Chocolate, dark, 45-59% cacao solids, April 2018. The USDA lists the nutritional content of thousands of food and drink products. 
[11] Mayo Clinic, “Caffeine content for coffee, tea, soda and more”, Mayo Clinic Staff, April 2017. Another great source detailing the caffeine content of common beverages.
[12] J Caine and T Geracioti, “Taurine, energy drinks, and neuroendocrine effects”, Dec 2016, Cleveland Clinic Journal of Medicine. A short article reviewing the current research on the effects of taurine.


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