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This question arose from my personal experience - after quitting coffee, I switched to drinking tea ( a lot of tea ). One day there was no tea, and I had a terrible headache, similar to the first days without coffee. A friend of mine suggested there is more caffeine in black tea than in coffee, and suggested green tea.

This made me wonder: how much caffeine is there in the average tea bag, as opposed to two teaspoons of grain coffee ? How about caffeine contents of other tea varieties ( green, white ) ?

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Black tea contains caffeine but less than coffee (~50-60% of it). Of course if you drink a lot more tea than previously coffee you can consume the same amount or more of caffeine. –  Martin Scharrer Jun 2 '11 at 15:14
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up vote 8 down vote accepted

Comparing the caffeine in a cup of tea with a cup of coffee (both brewed, prepared with tap water) on average:

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Bear in mind that these values values vary wildly according to where you look. The above data is averaged from a large number of sources, available here.

So, surprisingly, no. Brewed coffee generally has more caffeine than brewed tea. However, dry tea contains more caffeine than dry coffee (source) but since we don't usually eat dry coffee or dry tea leaves, it is safe to say your friend is wrong about caffeine content but right to suggest green tea as an alternative. Green tea contains around 25mg per cup.

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The values depend hugely on how you brew the tea (bound or unbound form caffeine?) and to a lesser extent on how you brew the coffee. I’m not really happy with such blanket values that don’t respect this variation. –  Konrad Rudolph Jun 2 '11 at 11:58
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@Konrad: they also depend heavily on what coffee and tea you compare. Just for example, Robusta coffee beans have ~2-3 times the caffeine content of Arabica beans. ico.org/botanical.asp –  user2046 Jun 2 '11 at 16:28
    
A tea cup is often much larger than a coffee cup. I don't know how Wolfram Alpha handles this. –  dancek Jun 3 '11 at 10:39
    
@dancek, if I'm not mistaken, US cups ( 0.2366L ) are used for both tea and coffee [ link ] –  Mihai Rotaru Jun 3 '11 at 12:12
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There is another effect that matters a lot and that is how fast the caffeine is absorbed by the body. With coffee it is pretty fast but tea contains a complex mixture of things like polyphenols that slow up the rate of caffeine uptake, so you get a gentler high. Even if you brew strong tea like a british builder. –  matt_black Oct 30 '11 at 20:56
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Quite Interesting had a question on this. https://www.youtube.com/watch?v=YwArLwsP3nA There's more caffeine in the same weight of tea leaves compared to the coffee beans, but less in a cup of tea than a cup of coffee.

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