I don’t think that the drug itself makes a subject tell the truth. It’s more probably that it leave them in a disorientation state that facilities an interrogator to get the required answers by leveraging that disorientation. To a degree is similar as many job interviews where is useful to create a climate of confidence so that the person being questioned feel more inclined to say things they usually won’t say. These things won’t be truths themselves but will facilitate an expert interviewer to connect the dots.