A street drug developed by the very people who are charged with policing it, Dust is a red powder that stimulates telepathic powers in humans (and some other species) for the duration of its use.
Dust was created by the Psi-Corps in an effort to create more human telepaths. It has been an unmitigated failure in that respect, and remains potentially a huge embarassment to the Psi-Corps should its origins become public. In the meantime, the same people who created the drug have the job of hunting down and punishing those who use it.
The fact that the drug works on non-human races, notably the Narn, is most likely indicative of the genetic meddling of the Vorlons with these races, with the drug tapping the telepathic genes implanted by that race.
Related drugs: Psi-blockers