I wonder how much better people would take it high or drunk. Maybe that's why they make you wait 4 hours, to let anything you may have taken to relax you wear off.
Cannabis edibles can easily exceed an effect duration of 4 hours.
Really though, the long interrogation time is probably so because people eventually become uncomfortable, being in the same state for such a long time. They want to see how you react in that situation.
Especially things like relaxants, maybe Valium or Vicodin, last about that time frame... and granted, these might as well be prescribed and perfectly legal!
