Keeping in mind that reduced oxygen, reduced air pressure, three-dimensional motion, visual illusions, stress, fatigue, and other factors can all influence the effects that even low levels of these things have, and not for the better, do you really want the guy in the front seat of your helicopter or aeroplane, or the guy about to do the live CAS or CCA run close to your position, even the slightest bit affected by any chemical?
Anybody who answers "yes" is a fool.
I would not, ever, willingly and knowingly, have compromised my ability to perform adequately and safely, as that guy in the front seat.
I never knew of anybody else, in my time, who did, either.
Had I, I would not have let it go unreported.
There is a lengthy history of deaths and aircraft losses due to problem people being left to continue foolish (not necessarily drug- or alcohol-related) ways with no correction.
Proper correction, early enough, can save a person when the problem is small and easily handled and before the result is catastrophic to their career or to people's lives.