If someone is so stupid they just have to go and get their dumbasses addicted to something that ruins their ability to keep a job, it's their problem, and there's no reason anyone should be taxed or have their liberties curtailed to keep those dumbasses from getting their substances of devotion.
Just use them as object lessons for kids: See, children, this is what voting for Democrats ....er taking some other toxic substance does to people. Don't be like them.
The employer can set any criteria for employment he wishes.
Also....by golly damn, drugs are illegal now....but there are still people on the shop floors, including a helicopter factory I know, who've been busted by surprise drug tests and fired. So the effort to keep those evil chemicals out of the workforce has failed.
Please keep that salient and inescapable fact in mind: The War on Drugs was never winnable, was lost, and we're still spending billions and billions of dollars restricting the freedoms of EVERYONE as a result of this failure.
Lost freedoms include:
Loss of the presumption of innocence.
Inability to carry larges amounts of cash out of the country, or even around the country.
Civil forfeiture laws incentivize law enforcement agencies to bend the rules and break other laws, and have resulted in the murder of innocent citizens.
Vehicle inspections at the borders.
Citizens stopped for routine traffic violations may be held on the spot until a trained dog sniffs their vehicle, in the complete absence of any probable cause.
etc etc etc