Eighty-one percent of large employers now require preemployment drug testing, up from 21 percent in 1987. Among all employers, the rate of testing is highest in the South. The drug most likely to be detected—marijuana, which can be detected weeks after use—is also the most innocuous, while heroin and cocaine are generally undetectable three days after use. Alcohol, which clears the body within hours after ingestion, is not tested for.
