I don't want to get in to all the ins and outs but my opinion is.
I wouldn't drink and drive!
I wouldn't take Co-Codamol and drive!
I wouldn't medicate and drive!
You are the judgment, you should never drive if you think you may be impaired in any way.
It just needs a way for testing to be accurate or a sobriety test of some kind.
Dunno, just a thought.