An almost completely reliable truth serum, Fast-penta is a commonly-used tool of ImpSec, the Barrayaran intelligence agency, and of numerous of its allies and enemies, too.
The drug itself relaxes physical tensions, as well as mental and emotional inhibitions. It is not so much that it compels honesty, as that it compels docility and helpfulness – which, in the hands of a skilled interrogator, amounts to about the same thing.
Artificial immunity to it is sometimes given to operatives by their agencies, and more rarely, some people have naturally idiosyncratic reactions to it, in which the effects are more similar to those of ecstasy or LSD – Miles Naismith Vorkosigan is one of these.
Related drugs: Synergine