Allswell is a chemical that naturally occurs in the human brain (at least, the humans of Arbre). It makes people feel a sense of well-being and optimism. Some centuries ago, it was genetically engineered into the plant named Blithe, which is a dietary staple throughout Arbre.
Throughout Arbre except in the maths, that is. The avout are forbidden to consume it – or even to grow it – and their time spent outside their maths is limited to ten days in order to stop it from starting to affect them adversely.
Snow Crash exists in two forms, although it’s unclear how similar their effects are. The first form is as a blood serum taken from existing users, which induces a number of effects, the most apparent of which is glossolalia or speaking in tongues.
The second form is as a cyberdrug, which specifically disrupts the thought processes (and Metaverse avatars) of experienced coders. This drug takes the form of binary code that is somehow able to derange the thought processes of those who look directly at it, leaving them, so far as medical science can detect, like the victims of an induced stroke.
Both forms of the drug are connected to a sinister cult that is apparently seeking to take over the world. It’s always something.