Drug tests greatly reduce the likelihood of hiding recent drug-using behaviors. Drug tests, like urinalysis, detect the presence of most drugs within 72 hours of use. After this window has passed, most drugs become undetectable. The exception is marijuana, which can be detected in urine for up to 30 days. Most drug tests cannot, however, identify historical use or drug dependence.
Drug tests can only stipulate whether an individual has used a particular drug recently .
Some welfare agencies have experimented with testing TANF recipients, but courts have blocked such tests on grounds of privacy. Nevertheless, it remains a common practice in employment.