Does coffee really give you an 'energy boost'? - Livescience.com

And the main way caffeine works is by changing the way the cells in our brain interact with a compound called adenosine(opens in new tab).

As we go about our days and do things, levels of adenosine rise(opens in new tab) because it is released as a by-product as energy is used in our cells.

While we are sleeping, energy use drops(opens in new tab) lowering adenosine levels as it gets shuffled back into other forms.

So eventually the caffeine breaks down, lets go of the receptors and all that adenosine that has been waiting and building up latches on and the drowsy feeling comes back — sometimes all at once.

Regular coffee drinkers might feel less of a caffeine "punch," with tolerance(opens in new tab) to the stimulant building up over time.

(Image credit: Getty)Caffeine can also raise levels of cortisol(opens in new tab), a stress hormone that can make you feel more alert.