To avoid addictive folks who will have a high incidence of no-show when on a binge. Or long absences while in jail.
It's interesting, because I've worked with a lot of people in a lot of places over the years and I've never seen drugs as a problem that impedes workplace attendance / performance. Alcohol / hangovers, sure - plenty of times - but they're not testing for that, right?
EDIT: parentheses content.
As i've moved up in job quality it has gone from "we will test you aggressively to see if you do drugs" to "why would we care about this?"
Practically it is very stupid because the heroin/meth/cocaine type drugs become undetectable within days while pot takes weeks.
It's a dumb US thing, basically.
That must be a new -- post 2007 -- thing, then.
I'm sure there are some ultraconservative companies that drug test everyone — including developers and senior managers — but those are few and far between in comparison.
Incidentally, it's quite awkward if you're currently employed when you get the new offer - as I was. The lab that collected the urine sample opened early in the morning for "regular" work but only accepted drug test samples from 10 AM to 3 PM on weekdays.
Outside of the red tape domains, like banking and government, I've never been drug tested as a developer. The idea that a low skill worker is more likely to be on drugs is classism. Low skill workers really get no autonomy. They are drug tested, have to clock in and out, and even have monitored lunch/bathroom breaks. It's kind of disgusting to think about.