With any drug that radically alters your state of mind, you're probably not going to be able to play DF, either because of incapacity, or because the influence of the drug is going to motivate you to do something else.
A stimulant would probably be the best kind of drug to play DF on, as long as you weren't geeked out of your skull. A small to moderate dose of something like adderall, or a generous dose of caffeine, or something like that, would probably reduce errors of omission, increase your focus on the game, and because of the general mood elevating effects would also likely increase your enjoyment. It would also be habit forming, and inadvisable.
A depressant would probably not be much fun, and you'd probably be happier listening to music or playing a less complex game, maybe something with flashy visuals that didn't require much though to enjoy. A game like Black and White, which has a generally slow pace, and a fairly simple interface, but pretty things happening and stuff going on on the screen even when you're not interacting with it- and which doesn't require your constant intervention- is a good sort of game if you have to take pain pills or something like that, having just got your wisdom teeth out, or recovering from surgery. Recreational use of depressants is a really bad idea, because they're notoriously easy to OD on, especially when mixed, not to mention habit forming and not really enough fun to be worth it.
A strong dose of a hallucinogen would take you straight out of DF-playing territory, but a mild dose could either prove to be incredibly awesome, a terrible idea, or just a lame flop. Hallucinogens are funny like that.