Coffee boosts metabolism and energy levels, making you feel more alert by interfering with the action of drowse-inducing adenosine in the brain plus activates the brain’s pleasure centers.
Does Coffee Perk Up Your Brain . . . or Not? - Source: psychologytoday.com
Excerpt: Caffeine is not stored in the body, so its effects are not permanent. Its impact can start to be felt ten to fifteen minutes after ingestion, and the effect lasts two to three hours.
Published in 2011 - I believe it is still relevant;
Why coffee perks people up - Source: www.health.harvard.edu
Excerpt: Once it reaches the brain, caffeine probably has multiple targets, but the main one seems to be adenosine receptors. Adenosine is a brain chemical that dampens brain activity. By hogging its receptors, caffeine sets off a chain of events that affects the activity of dopamine, an important neurotransmitter involved in mood.
Published in 2012 - I believe it is still relevant;