Two Molecules, Opposite Effects

Caffeine (C8H10N4O2) is a stimulant that blocks adenosine receptors in the brain. Adenosine builds up during waking hours and makes you feel sleepy.

Alcohol (ethanol) is a depressant that enhances the effect of GABA, the brain's main inhibitory neurotransmitter, while blocking glutamate, the main excitatory one. This dual action explains why alcohol simultaneously relaxes muscles and impairs coordination.