A coloured diagram of your favourite recreational drug.
(From Wikipedia: Caffeine is a xanthine alkaloid compound that acts as a stimulant in humans. Caffeine is sometimes called guaranine when found in guarana, mateine when found in mate, and theine when found in tea. It is found in the leaves and beans of the coffee plant, in tea, yerba mate, and guarana berries, and in small quantities in cocoa, the kola nut and the Yaupon Holly. In over 60 plants, it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants.
Caffeine is a central nervous system (CNS) stimulant, temporarily warding off drowsiness and restoring alertness. Caffeine is the world's most widely consumed psychoactive substance. In North America, 90% of adults consume caffeine daily.)
And it's legal!
(If you'd like something stronger - testosterone!)