More than 73 percent of drug users ages 18-49 are employed, accounting for more than 8.3 million U.S. workers.
About 2 percent of all positive specimen tests show evidence of substances to mask or compromise the results.
Only about a quarter of U.S. workers in a 1997 study reported a drug-testing program in their workplace.
According to a 1996 study, 11.5 percent of employees making plastics and rubber products said they had used drugs during the past year, while 4.1 percent said they were heavy alcohol users.
Sources: Department of Health and Human Services' National Household Survey on Drug Abuse; Quest Diagnostics Inc.