There are drugs in Daggerfall, and a few Noble and Thieves Guild quests involve trafficking them.
They are Indulcet, Sursum, Quaestro Vil, and Aegrotat.
For more information (mostly as pertains to gameplay), I'm just going to include an old post:
Alright, I did some poking around, accepting tons of thieves guild smuggling quests and eating the goods. And the DF Chronicles had some info as well. So the following is a compilation of both our efforts.
Daggerfall drugs
Drugs have 2 effects, a primary bad effect and a secondary good one (both are save vs poison). You almost always get the bad one, and hardly ever get the good one. (the only good one I managed to get was from Quaestro Vil.) Because of this, I do not know if the positive effects are permanent or not (temp fortified strength versus a permement increase). Secondary effects are also supposed to carry a "hallucination" effect, but I've never seen it in action, and would bet that, like so many other things, it didn't make it into the final game.
Indulcet: http://i6.photobucket.com/albums/y217/Jormungandr83/DFIMG/Drug2.gif. moderate onset time, relatively low duration.
1. damage to fatigue
2. increase in luck
Sursum: an amber powder (identical to indulcet). Low onset time, low duration.
1. heavy damage to intelligence
2. heavy increase in strength
Quaestro Vil: http://i6.photobucket.com/albums/y217/Jormungandr83/DFIMG/Drug1.gif. low to long onset time, low duration.
1. low damage to willpower
2. Increase to fatigue
Aegrotat: an amber powder (identical to indulcet and sursum). Instantaneous onset, very long lasting.
1. low damage to endurance.
2. increase in spell points
They have no other descriptions in the game, other than a quest description that refers to %random_drug as "a highly addictive herb" which, because it picks a drug at random to describe as such, isn't helpful.
All drugs are treated as poisons while they are taking effect; afterwards, you seem to get "witches' pox" (one of the diseases in game), but this version of the pox doesn't actually do anything, although you are still treated as diseased (and get warnings when you travel--don't worry, you won't croak from it). Since I believe you can only be inflicted by one disease at a time, it goes to say that leaving yourself inflicted with this inert strain of witches' pox would be an effective immunity to disease. But that is just a gameplay quirk.
[update!] I just got the positive effect from Aegrotat as well. It would be awesome is Sursum would work.
[update2] HAHAH!!! I just attained the Sursum secondary effect. Strength shot up to 100, and it is permanent--until you cure the disease. The "witches' pox" is what keeps the drugs effects in effect. So if you use "heal attribute" spells to cure your intelligence, and never get that disease cured...
Drugs. Are. Awesome.