Alt,
After reading your original post I need to chime in.
Your attorney is right but also flat wrong. I used to be a trucker and I know the D.O.T. prohibits driving while taking certain drugs even if prescribed. I also know some drivers do it anyway. That don't make it right!
If a drug effects your ability to operate a vehicle in a safe manner you're liable to get a D.U.I. This is one reason that you have to have a prescription drug in it's original container. If the drug is unsafe to operate a vehicle or machinery it's labeled so. And they do check, trust me...