For all that we know about this substance, caffeine is very seriously misunderstood. Caffeine is not a simple boost to your body; it works differently on everyone and people have different tolerances for it.
Caffeine does not just increase your body activity like sugar does; it goes right into your brain and binds with receptors in your brain that detect levels of adenosine, which, if there is a low amount of this, your body will tell itself to go to sleep. What caffeine does is it goes straight for those receptors and floods them, clogging them.
With the receptors blocked, the brain’s own stimulants, dopamine and glutamate, distribute freely with in the brain. So let’s review really quickly: caffeine does not do anything to your body besides blocking receptors — everything that increases this is your own body’s stimulants.
The effects of caffeine will vary greatly from one person to the next. Length and strength of caffeine effects depend on genetics and other physiological factors including tolerance.