The govt. shouldn't be able to drug test anybody. Nobody should.
There is a 4th amendment to the Constitution...and I believe that any drug test, any breathalizer test, etc. is a direct violation of the constitution.
That's why you actually have a choice to take them or not.
Of course the govt. has figured out that they can penalize you for NOT taking them. So everybody falls in line and allows their work or govt. to take their blood (or you lose your job)...or take a breathalyzer when you get pulled over (or you go to jail).
So yeah, the govt. COULD require a drug test for welfare.
But all of the above "testing" is very much against the intentions of the Constitution.
How could there be any more drastic of an invasion of privacy than drug testing?
Our "freedom" isn't exactly Freedom. You are "free" to do whatever you like...unless religious fanatics disapprove.
One other thing...the epidemic of drug use these days is prescription opioids.
How the hell is "drug testing" for cocaine (which folks on welfare probably can't afford) and pot (also expensive as hell these days) having any effect on the REAL problem of prescription pills?