Scenario. Unlikely but possible.
6am on a monday there are 5 pilots all in one room, 2 going home after night shift & 3 coming on for the day shift.(Not to mention 2 engineers) All are spot tested in the office on that cold monday morning. The 2 night shift pilots both took a pill to assist in a headache from having slight head colds (could be toothache/backache also). All 3 day shift pilots have been tested positive from a variety of drugs/booze (all legal as in over the counter stuff) still left over in their system from say a staff party the previous sat night (that's 2 nights ago seeing as it's monday morning). All 5 pilots are stood down right there & then. I'll just tell the Ambulance Service that the days flying & possibly the next few days is either off altogether & or seriously restricted!!!. That's fine am sure the sick & dieing can wait
Hypothetical & a long shot I know but...what if??
You don't even need that many 'hit' at once to have a huge effect on the goings on in Aero-med.
Oh & just as a side note the drugs etc that are in the back of our planes would make a sniffer dog curl his toes up!!
CW