As you probably know, black tea is a good source of caffeine. The amount of caffeine in a cup of black tea depends on how strong you make your tea. One cup of black tea can contain anywhere between 40 and 70 milligrams (mg) of caffeine. Even decaffeinated tea can contain up to 12 mg.

As a result, black tea can help boost your mental alertness and concentration, without too many side effects.

Normal Tea – 26,2 mg / cup
Black Tea – 47,4 mg / cup
Coke  – 29,4 mg / can
Red Bull – 77,4 mg / can
Coffee – 94,8 mg / mug

While the side effects of black tea are mild, its caffeine content can cause nervousness and excitability.