Years ago at university I participated as a subject in a memory study that involved the injection of scopolamine. I was familiar with it's reputation as a truth serum and very curious to feel the effect.
But it's utter nonsense. There was little more than an awfully dry mouth and a short-term memory so impaired I felt stuporous.
In my opinion any euphoriant will elicit more truth telling than scopolamine.
This in itself is really beneficial as a truth serum. By enquiring multiple times the victim can't remember their previous answer, so therefore reveals which parts of their story are true and which are fictitious.
There we have to distinguish between dishonesty and a lie. A deliberate construction on the spot might not survive multiple angles, this is the basis of interrogation rooms after all, anyone will trip themselves up repeating versions over and over again.
What won't necessarily find the light of day is deception, a pattern of behavior. A drug dealer might get caught up in where he was or who he was with at a given time on a given date, but he'd have to be intellectually impaired to admit he was a professional criminal for a living.
But it's utter nonsense. There was little more than an awfully dry mouth and a short-term memory so impaired I felt stuporous.
In my opinion any euphoriant will elicit more truth telling than scopolamine.