What would be on that list of banned substances? 


That would include all illegal drugs including marijuana.  We should put alcohol on there since 10.8% of unemployed workers report heavy drinking [3].  Many prescription drugs are just legalized versions of illegal drugs.

What would be considered a failure of the test? 


If they test with any alcohol in their system?

Have no prescription for the prescription drug they test positive for?

They have been on a prescription drug with prescription for X years? Do we pay to have them evaluated by a psychiatrist or doctor?

False positives [1]? How many times do they have to fail?

What about? 


What if they are a parent?  I assume we must take the children away from the parent instead of letting them starve?

This includes welfare, food stamps, and unemployment?

Why not treatment [4]?

The fact that a lot of these people will be mentally ill women with children [5]?

Scenarios... 


So when a mother of three has a drink or smokes a joint to calm her nerves because she lives in a car and can barely feed her children.  We should then stop giving her welfare and take her children away from her?  

What about the false positives?  Someone gets a false positive and subsequently can not get unemployment to pay rent. They then  lose their apartment and can not get a new job because they have no physical address.  

Is the person who smokes a joint only at concerts or does cocaine once at a party better worse or the same as the person who drinks half a gallon of vodka every day? How do evaluate that with a drug test?  

What about the person who is addicted to Oxycontin, Xanax, and ADD drugs [2]?  How does that change if they have a prescription or not?

Closing


I am by no way completely against the idea.  Sure there might be a way to do this effectively (treatment maybe?) that won’t make the problem worse, but I really doubt it.  All I am asking people is to discuss and debate it not just drop an uninformed opinion in.