Coffee is a morning constant for many, as reliable as the sunrise or the tides. Miss it, and you can feel dazed, confused, and even risk a pounding headache. There’s a good reason for that: Caffeine produces some reliable physical changes in your body upon which you can easily become dependent.
With that first sip of Joe, caffeine enters your bloodstream and begins making its way to your brain where it blocks an inhibitory neurotransmitter called adenosine, according to the National Academy of Sciences. That, in turn, sets off the release of feel-good hormones like dopamine and serotonin, causing a stimulant effect. Coffee’s so-called half-life—meaning the amount of time it takes for the amount of caffeine in the body to be reduced by 50 percent—is about five hours on average. That explains why the average energy drink or coffee buzz lasts about that long. But how quickly caffeine leaves your system depends on a number of things, including age, medical conditions, drug interactions, and lifestyle habits (like smoking).