"You don't think other people have rights in the workplace to be free of dangerous individuals that can cause them injury or death?"
If THAT were your goal, just testing for impairment, whatever the cause, would be sufficient. Say a simple test of reflexes and mental agility when clocking in in the morning. If you are impaired, NO MATTER THE CAUSE, you get sent home.
But I suspect you want folks tested (and busted) for ILLEGAL substances. Because you are a control-freakazoid, authoritarian busybody, am I right?
No, because their are inconsiderate a-holes like you who wouldn't think twice about putting others in danger because of chemically impaired judgment.