Lifehacker explains that it’s not really an upper, but an impersonator which mimics adenosine – the byproduct or “excrement” produced by neurons as they fire, the build-up of which nudges your body towards sleep or taking it easy.
The brain’s adenosine receptors get tied up, freeing the brain’s natural stimulants – dopamine and glutamate – to do their thang. Their sweet, sweet thang…
“Like taking the chaperones out of a high school dance” or “putting a block of wood under one of the brain’s primary brake pedals” (as opposed to stepping on the gas).
I loved the cartoon – more on its origins and effects at The Oatmeal.