A perfectly legal drug developed by the Psi-Corps in order to suppress the telepathy of those psis who do not wish to join the Psi-Corps.
Psi-blockers take about three hours to take effect after they are administered (via direct injection), although the dosage size seems to affect how long they last for – a standard dose for a registered telepath lasts for a week. Unfortunately, doses that large have the unfortunate side effect of causing depression in long term users (although sociopaths seem immune from this effect).
Related drugs: Dust.