I cant see what the problem here is guys.
If you're on medication then fine - as long as it is within the confines of acceptabilities as prescribed by the CAO's.
(ie: Antibiotics and other non stimulants).
As far as being detected with something in your system you would undergo counselling by a company doctor and retested.
Those not indulging in say ecstacy (MDMA - whose use is ripe amongst some members of the aviation industry), Cocaine, Heroin,Marijuana,speed etc or even anabolic steriods (non subscription) have nothing to fear.
Judging by the number of people operating machinery/equipment at airports in the USA that have tested positive to class A drugs then I reackon its about bloody time.
Even in Japan some airlines have their pilots blow into the bag at sign on.
Bloody good idea I reackon.