One of the more effective truth drugs out there, TC-6 is typically used only by government agencies for interrogations. Administered via direct injection, it leaves those it is administered to able to respond intelligently, although it will make most people somewhat literal-minded. It will also leave them utterly without volition of their own and thus unable to lie.
It is possible to resist the effects of TC-6, although to do so requires considerable experience with truth drugs, and a certain amount of psychological conditioning, as well.
Very few people have this conditioning, however, so the drug remains useful. A single dose will last for several hours, although the drug is known to have certain side-effects regarding impaired cardiac function in some people – potentially fatal side-effects – and there is no test to determine ahead of time who will suffer them.