There is no shortage of reasons employers test their workers for drugs. At one company, an employee high on marijuana forgot to lock the wheels on his forklift and it dropped five feet off a loading dock, while employees at another built a crystal meth lab in the back of a truck.

Workers who use drugs raise a company's insurance costs, steal equipment and scare away clients.

"The drug and alcohol issue is a concern for America," says Mary Wheeler, co-owner of Wheeler Landscaping in Chagrin Falls, Ohio, who began screening job applicants five years ago and now randomly tests her 76 employees. "Until you have a drug-free workplace you don't realize how prevalent it is."

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