I've never been drug tested at work. Maybe they assumed that anyone with really interesting security clearances, and who were used to safety critical work where if you screw up, people may die, perhaps thousands of people, would be so risk averse as a matter of culture they'd be careful about any psychogenic materials, legal or not.
I have been breathalysed a dozen times or more, because we have RBT - random breath testing. Police set up a checkpoint, and pull over vehicles at random.
Personally, because I have an unusual metabolism, with non standard neurotransmitters, it's wise to play it safe. I have a strong allergy to the plant cannabis sativa, meaning dope smoke acts like tear gas on me, and I get sneezing fits if I enter a room where grass has been smoked in the last few days.
I have a high tolerance for Pethidine (Demorol), Fentanyl appears to have no effect, Morphine hyper effect, BP and heart rate crashed with a 'test to see if safe' dose, Codeine phosphate normal.
The things you learn when being taken to resusc in an intensive care ambulance. Apparently I have ridiculously large numbers of Kappa receptors, but little in the way of Mu or Delta ones.
I guess the point I'm trying to make is that one should be prudent about the use of psychoactive chemicals. Humans vary in their responses. A dose that is safe for 99% of the population might be very unsafe for some of the other 1%. Best is to try microdoses first under medical supervision, or, if known to have anomalous responses like me , steer clear unless necessary.