Business owners interested in setting up a drug screening program should consult a lawyer first, as rules vary by state.

While Ohio encourages drug testing, states like Vermont and Rhode Island specifically prohibit company wide random screens. Minnesota and Vermont require employers to offer workers a chance at rehabilitation the first time they test positive.

Nancy N. Delogu, a labor lawyer at Littler Mendelson in Washington, says these state worry about violating workers' rights. Those laws were passed in the early days of drug testing, she points out, when lawmakers were concerned that false positives could lead to damaging accusations.

To make it work, employers should clearly communicate the details of a drug policy to employees and ensure that workers understand the consequences. Equality is also important; chief executives and heads of personnel should be tested as frequently as everyone else.

Once an employee fails a random test, business owners have a choice. Some employers immediately fire the guilty party, while others prefer to give employees a second chance.

"I usually recommend an auto-termination policy where the employer does not have a good rehabilitation program," said Heather Gatley, general counsel at the human resources company AlphaStaff Group. "However, you have to defer to the tolerance level of the company." Small companies or family-run businesses often go to great expense to rehabilitate loyal or long-term workers.

More important, employers should not jump to conclusions. Tests occasionally yield false positive, and employees who are legitimately taking prescription should not be penalized.

Sometimes, however, there is no doubt about a drug user's habits.

Mary Wheeler, co-owner of Wheeler Landscaping in Chagrin Falls, Ohio, says one job applicant, when informed of the pre-employment drug test, assured the interviewer he would pass it. While filling out his paperwork, the interviewer asked the applicant for a driver's license. The applicant reached into his pocket, and by accident pulled out a small bag of cocaine.