truth serum
truth drug

The drug has long been discredited as the "truth serum" it was once said to be.

Do you think I'll give you a truth serum or something?

This one is your agreement to take a truth serum in the event of a dispute.

Back at the hospital, he is given truth serum.

"Why did she have the truth serum if she was to just bring us in?"

The poison of choice happens to be a deadly truth serum.

She was trained in the use of that drug, the most powerful truth serum yet discovered.

When people drink it, the rum seems to act as a truth serum.

Doctors would use a type of "truth serum" to get soldiers to talk about their experiences.

What did they give you, some kind of truth serum?