With safety-net spending under review around the country, proposals to make welfare and unemployment checks contingent on drug testing have become a routine rallying cry in dozens of states.

But the impact of drug-testing measures has been limited.

Supporters say the tests are needed to protect welfare and unemployment compensation funds as the nation emerges from the recession. But their enactment has often been hampered by legal challenges and the expense of running the programs, which generally uncover relatively few drug users.

Drug testing of welfare recipients in Florida was halted by a federal judge. The rollout of a similar program in Georgia was suspended indefinitely as a result of the Florida ruling. Measures in other states have been narrowed in scope, primarily to keep administrative costs low and avoid protracted court battles.

This week, legislators in Michigan, after failing to agree on more robust drug-testing bills in recent years, approved a measure that would withhold unemployment compensation from people who fail drug tests given as part of job interviews. The approach, a one-year pilot program, leaves it up to prospective employers to screen applicants and does not force businesses to test or report the results.