The most commonly and widely abused drug is alcohol. Certain forms of employment screen for other chronic drugs because it might affect your doing of
the job.
In far north western Australia there's been a recent 'intervention' of sorts to stamp out alcohol abuse in remote Aboriginal communities - the
cycle is welfare day comes, all the money is spent on booze, and everyone waits for next pay day.
All alcohol going into the communities is accounted for by the bottle shops by taking the names of people who buy it and putting limits on how much
they can buy.
The pay day- > booze cycle though is also among some of the wider community - but to suggest the same would be done in metropolitan areas would tick a
lot of people off.
As for screening for drugs, it'd upset a lot of civil liberty people. It's in an invasion of privacy - but I agree with the idea behind it.
Especially the dealers who get welfare!