It depends on your sensitivity to it and how much you drink. But, you personally should know your own effects to it. I'm pretty sensitive to it, so I only drink 1 cup and that wakes me up and makes me focus, especially since usually I wake up earlier on exam days to cram. But drinking say, 2 cups as well as my tiredness can make me a bit hysterical and I laugh over nothing and can make my hands a bit shaky. If you have an abnormally fast heart beat anyway (like I do), the coffee will increase your heart rate even more and you're breathing can get a bit weird as you can get (I think it's called) heart palpitations, which has happened to me quite a bit. But it's nothing major, it just increases your nervousness in the exam. Take 'rescue remedy' for that :3