This is just a small idea that I hope could be added into later versions, to give some variety to gameplay and maybe introduce a new layer of complexity to criminal groups. To put it simply, the idea is this- have certain substances with randomly generated effects, be they positive or negative, created in worldgen. They could be anything, from the blood of a rare beast, to a certain plant extract- anything. These substances would be in circulation, and if taken, there is a chance that the character could become addicted (perhaps depending on their disease resistance or willpower?)
The substances, as previously mentioned, could have a range of effects. They could keep a character "focused", increase their strength, give them pleasant hallucinations, make them feel positive... Or, as drawbacks to their benefits, they could sap strength, reduce general happiness, or give the character a "bad trip"- something like bogeymen hallucinations appearing onscreen and chasing you down. Thus, it'd be a gamble to take these drugs, and withdrawal symptoms could be severe.
Depending on a civ's stance on drugs, they could be sold in taverns/apothecaries, or outlawed, only to be attained from criminal organizations or bandit groups- for a higher price, naturally.
What do you guys think? Could this add something fun to the game?