In the hitchhikers guide to the galaxy there's a man called Prak. Prak was a witness at a trial and was given truth serum.

“They gave him too much,” he said in a tiny whimper.

“And when the trial continued,” he said in a weeping whisper, “they asked Prak a most unfortunate thing. They asked him,” he paused and shivered, “to tell the Truth, the Whole Truth and Nothing but the Truth. Only, don’t you see?”

He suddenly hoisted himself up on to his elbows again and shouted at them.

“They’d given him much too much of the drug!”

​

“Terrible things, incomprehensible things,” he shouted, “things that would drive a man mad!”

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I imagine something similar might happen.