A couple years back I was GMing in a 3.5 D&D group and I had just discovered what entheogens were, so I decided to include stuff like that in the game for laughs -- spirit quests, bat country, jesus christ what are these goddamn animals, someone's been giving them liquor -- a little less Cheech & Chong and a little more Fear & Loathing.
One of the drugs was an herb with blue flecks in it that would crop up where potent time magic was used. It provided bonuses to Initiative, a dodge bonus to AC, and a bonus to Reflex saves while under its effects, as it altered your perception of time and slowed things down.
The comedown had the opposite effect, however, and everyone seemed to be moving and speaking in fast-motion, giving huge penalties to Initiative, AC, and Reflex. It was kind of fun talking really fast to the players who had taken it, to the point where they couldn't understand what I was saying, while roleplaying a terrible headache.
There was also the time when the human psion and the half-giant psychic warrior went on an all-night bender and woke up in a ditch a mile from town, spooning and wearing one another's clothing.