Screening potential employees for drug use is not as easy as it sounds. You cant just go up to an employee and ask him or her to submit to a drug test, especially if they already work for you. Everyone has legal rights to privacy and your actions can be seen as discriminatory. There is a very fine line that you have to walk and that means knowing the laws.
According to the Americans with Disability Act that governs drug testing, a person must be offered the job before you can ask them to test for drugs. Also, it is usually an expense incurred by the employer. The potential employees past drug use should not be a factor in determining if you want him or her to work for you or not. If they no longer use the drugs then it should not be a factor.
Every state has different laws governing the hiring of employees in relation to drugs. If the work environment has the ability to pose danger to the workers if the equipment there is not used with care is a good reason to get everyone that works there or want to work there tested for drugs. You must also find evidence of presence of drugs in the building or strongly suspect an employee of using drugs, seeing symptoms of drug use, like if someone become delusional. The law actually protects people who already work for you. The evidence must be so strong that you are forced to confront an employee. If something like that doesnt exist and you try to force an employee to take a drug test then it can cost you a few million dollars in lawsuit money. So remember to be careful and always investigate before asking someone that already works for you for a drug test.
Drug testing is a standard practice in the business world today. With the advent of every kind of drug that has ever existed and the disastrous effects that it can have on work and fellow workers, most companies are asking for drug testing. Just make sure you have made the job offer before you ask them.