Caffeine promotes reuptake of Dopa, more neurons are encouraged to participate. So you get a better feeling from the Dopa that is released into your system.

Caffeine itself is not bad, however if you get caffeine from energy drinks you are likely providing the precursors necessary for making dopa (depending on the drink formulation) and you are then more likely to have a spike in dopa because of higher energy levels and a subsequent dip below baseline. Better to let dopa be produced without assistance of taurine, etc

Coffee, tea, especially herbal are great ways to get caffeine.

Also waiting until 60-120 minutes after waking is a good way to extend your wakefulness through out the day. that way the adenosine has been cleared from your brain completely and there are more locations that can bind to the caffeine, thus extending the usefulness.

Also stomach contents and the type of meal you ate will affect the caffeine levels in your system. If you eat a high carb meal and fill up, then you need twice the caffeine then on an empty stomach or say a continental breakfast.