How much caffeine is safe per day?

That is roughly four cups of brewed coffee, since an average 240-millilitre cup contains about 95 milligrams. A single espresso shot has around 63 milligrams, a cup of black tea about 47 and a can of cola roughly 30 to 40. The European Food Safety Authority advises pregnant women to limit caffeine to 200 milligrams a day. Caffeine works by blocking adenosine, a chemical that builds up in the brain and makes you feel sleepy. Its effects fade slowly, because the body takes about five hours on average to clear half of it.