One of the interesting features of EVE Online is that it has a drug trade in which players are actively engaged. Rather than merely being an illegal commodity, drugs -- called boosters -- enhance the performance of EVE's pilots, albeit with some potential side effects.
To understand boosters though, we'll need to look into the game's setting a bit first. The thing to remember is that as a player, you're a capsuleer. You're not standing on the bridge of your ship barking orders at subordinates. Rather, you're floating inside a metallic capsule deep within your ship. Your mind is interfaced with the ship you pilot via neural implants, thus your vessel is an extension of your body and its senses; you regulate the ship's activities merely by thinking about them. Not all people in EVE's setting of New Eden have the raw potential to become a capsuleer, making your character one of the elite. However, when faced with others of your caliber in combat, every possible edge you can gain over rival capsuleers helps. That's where boosters come in... they're your edge. Boosters augment aspects of your mental processes and thus provide certain bonuses when piloting your ship.