> Florida did drug testing as a condition for welfare benefits... and it cost more than they saved

It's more complicated than that. Of the 6352 people who applied for TANF, 2306 dropped out during the process. Then of the 4046 TANF applicants remaining, only 2.6% tested positive for drugs. The vast majority of media coverage focused on the 2.6% being less than the ~8% drug-use rate in the general population.

What we don't know is of the people who dropped out, was this due to unintended reasons (privacy concerns, the inconvenience of the drug test, missing deadlines) or due to the intended reason (people self-selecting out because they knew they would test positive and become ineligible for 12 months). We'll never know the real breakdown, but it's misleading to say "it cost more than they saved".

The state tries to take kids away from people who use drugs, so I would expect custodial parents to be below the average drug use of the general population.

Nah, the article addresses that theory too.

> An internal document about Temporary Assistance for Needy Families, or TANF, caseloads stated that the drug testing policy, at least from July through September, did not lead to fewer cases. “We saw no dampening effect on the caseload,” the document said.