I trained as a school bus driver, and when we got drug tested, a lot of over the counter stuff could show up. We were also not allowed to drive under the influence of any drugs that had not been cleared, even prescription. And clearing a drug was on a case-by-case basis, though it mostly operated on the honor system.
What an archaic and backwards viewpoint. Any state in the US where pot is legal, you can find plenty of responsible weed users, the same way you can find people who drink alcohol responsibly anywhere.
I don't think even you believe this, unless you're willing to bite the bullet of alcohol and coffee prohibition? They're the most central, widely-used psychoactive drugs in the world, and after all, "a drug is a drug".