There's no way for them to tell if someone's impaired from the amount of THC in their system. Some ultra-low tolerance people would be too stoned to drive from a 2 mg edible. Some medical users can consume a gram a day of oil and be fine to drive. Some get to the point where they can't even get high from oil.
THC doesn't work the same way as alcohol. Heavy drinkers can't consume 500 times the alcohol as a light drinker and actually survive or be functional.
THC doesn't work the same way as alcohol. Heavy drinkers can't consume 500 times the alcohol as a light drinker and actually survive or be functional.