It should be possible to create powerful potions without the use of any strictly magical ingredients or enchantment, since many plants produce chemicals that cause... interesting effects when ingested. With some cleverness, it's possible to use these effects to create plot points. A particularly pertinent example would be the apple given to Snow White of the Seven Dwarves. Although we don't know the exact nature of the poison, we do know that it put Snow White into a deep, magical coma, and therefore had a depressant effect. It might very well have been deadly nightshade, which seems to be a popular poison in literature, and also has a very strong depressant effect.
Not every drug has to be so strong, of course, nor need they be extracted to be used. It should be possible to use some drugs just by eating the plant, as many stimulant leaves are chewed to provide a mild buzz. Others might need to be cooked or similarly processed before they are palatable, such as coffee or chocolate, or activated, as liquor.
Of course, it'd be good to quantify the effects of these drugs if they're to be randomized with worlds. Some important attributes:
- Depressant-stimulant axis: Drugs in the positive would reduce or even eliminate the need for sleep, increase speed, and eventually kill with a heart attack. In the negative, speed would decrease, tiredness would increase, followed by coma and death by respiratory failure.
- Intoxication: The more intoxicating a drug is, the happier it makes you feel, and the more impaired your judgement. Since PCs are currently emotionless, impairment would be the most noticeable effect for intoxicated players.
- Anesthesia-analgesia axis: In the positive, the drug removes pain, either locally or generally. In the negative, it removes all sensation, again either locally or generally. General anesthesia is a very dangerous thing, however.
- Hallucination: Everybody's favorite, but it shouldn't take so whimsical form as in Nethack. Severe hallucination obviously would lead to incapacitation, but less intense hallucinations might make friend turn against friend, believing each other to be shape-shifting demons or otherwise hostile creatures. Mild hallucinations might change creatures to something closely related, such as a rival into a close friend, a mayor into a diplomat, or a dog into a larger and more vicious dog. The possibilities are potentially limitless, especially if enchantment allows you to project the powers onto others.
Exceptions will also probably have to be included. For example, liquor seems to be a stimulant rather than a depressant for dwarves, and is less intoxicating. Catnip is intensely intoxicating for cats but inert for everybody else. Goblins get off on some kind of fermented blood beverage, according to one of the stories.