According to an article in the Houston Chronicle, workplace drug testing lets employers ensure their employees are not using illegal drugs on the job or during their time off. The following is from the article by Emily Weller, of Demand Media

Ensures Employee Safety

Some jobs are dangerous to perform even if a person is completely sober. Using heavy equipment or driving a truck requires an employee to be alert and not under the influence. For example, an employee working a deli counter should not be using drugs while handling sharp knives and working over a hot stove. Drug testing before a person goes to work will ensure that he doesn’t work while under the influence, protecting himself and other staff from potential accidents.

Avoiding Problems Down the Road

A company may decide to screen all potential hires to prevent problems that can arise from persistent drug use. A drug problem can quickly spiral out of control, and someone who may seem like a good employee when hired can soon become unreliable, showing up late to work or not focusing on his duties. Paying for a drug test upfront may save a company money later on, when it does not have to re-hire or compensate an injured employee.

It’s Required

In some cases, testing employees is a requirement. Companies covered by the United States Department of Transportation must test employees for drug use. Covered companies typically include public transportation agencies, airlines and railroads. The Drug-Free Workplace Act of 1988 requires some companies to test employees if they wish to obtain a contract with the federal government. In addition, if a company receives a grant from the federal government, it must test its employees for drug use.

Fairness

Some companies may drug test employees to ensure a sense of fairness. In 2011, the governor of Florida required state employees to submit to drug testing. Since employees of the state are paid with taxpayer dollars, the governor felt it fair to have them undergo drug testing so that residents of the state know they are not funding drug use. In addition, Florida passed a law requiring those applying for the state’s Temporary Assistance for Needy Families to submit to a drug test before they can receive money.