Depending on who you ask, you will most likely hear different jokes about which one is better, while others still say that they are better if they are combined at the same time. Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two energy shot drinks. Keep in mind that the actual caffeine content in beverages varies widely, especially among energy drinks. We will also look at mixing Adderall and modafinil together — why you might want to do it and how to do it safely. Here we will show you what makes these drugs different and which one is better for you to use to increase your productivity at work or at school.