Praxis was a chemical compound often used as a drug. Though genuine documented cases were rare, a powerful urban myth grew up around them. Despite being called "the Holy Grail of hallucinogenics," praxis was not a drug but a compound of several elements that defied subatomic analysis and were unknown in the Spiral Politic's periodic table. Instead of generating subjective hallucinations, it created spontaneous and temporary mutations of the Spiral Politic itself.
The only known producer of the drug was the Pilots' Coterie, whose used it to distort the continuum in their calculations of space-time events for piloting ships like the Bababadalgharaghtakamminarronnkonnbronntonnerronntuonnthunntrovarrhounawnskawntoohoohoordenenthurnuk. Their praxis took the form of a tasteless gelatinous biomass, and humanoids needed to ingest at least 10 times their own body weight before it had any useful effect. However, there were doubtless many more efficient sources beyond the frontier in time.
Praxis played a role in Earth's history, as well. The Sargossa manuscript, recovered in the early nineteenth century by Count Potocki, recounted von Worden's experience of becoming trapped in a series of nested and regressive states of existence. (PROSE: Praxis) The Rivera Manuscript described a similar praxis fugue, this time forced on a renegade of the Great Houses by the enemy. It apparently depicted a version of the enemy's first invasion of the Homeworld. (PROSE: Notes on the Rivera Manuscript) A note on the manuscript, written in English but by an alien hand, said, "Praxis is not a drug. Praxis is not a weapon. Praxis is not a training manual. Praxis is what we were meant to become." (PROSE: War Predictions)
House Xianthellipse sponsored the ruling caste of a posthuman colony to produce the drug for them; Robert Scarratt became addicted to praxis during his time working there. Under its influence, he (reportedly) single-handedly defused a local uprising caused by native resentment at the rulers' high-handed attitudes. In reality, his native contacts undoubtedly played a major role. (PROSE: Robert Scarratt)
Godmother Antigone sent Cousin Rupert to Bankside to investigate Haribeaux's Blue Praxis experiments; however, these claims were really just an excuse to ensnare Rupert into Father Christèmas' plan. (PROSE: Weapons Grade Snake Oil)
The Doctor was susceptible to gases in the praxis range. (TV: The Caves of Androzani, AUDIO: Planet X)