Drug testing should ideally be conducted in a laboratory environment. There the testing methods, samples and results will be most pure and reliable. Usually, a drug testing lab contracts with corporations and organizations to provide the service as often as needed. The labs may test only the newly hired employees of their clients, or sometimes labs will provide random testing of employees. This is useful when there is suspicion or frequency of drug use with one employee or a group of employees. It is also useful when operation of heavy machinery or a motorized vehicle is part of the job description. Typically, in these cases, the employees of the companies and organizations contracting with the lab will visit the lab to undergo drug testing during business hours. Urine sample testing is most commonly used in such labs.

Following an accident or injury, a person might be tested for the presence of drugs in the system. This so-called post-incident testing helps determine whether a person was under the influence at the time of the accident and whether criminal charges or a lawsuit should be filed in the future. In the case of an on-the-job accident, it can determine whether the employee is eligible for workman’s compensation to pay for treatment of their injuries. Whether the accident occurred on the job, on the road or elsewhere, it will most likely involve a blood draw at the hospital’s emergency room. In the case of an accident on the job, the blood sample will most likely undergo toxicology testing at the lab that the company contracts with. In other instances like vehicular accidents, where legal consequences may be involved, the blood sample will most likely undergo toxicology testing at a government laboratory. These labs often have backlogs due to the high number of tests they must handle, so test results can take several weeks. If hospital admission is not needed, like in a vehicular accident, the officer working the scene of the wreck may utilize police training and skills to analyze whether the driver is under the influence of drugs.

The legal system might order a parent to undergo random drug testing in the case of child custody cases, to ensure the safety and well-being of children. This will typically be conducted at a private drug testing facility hired under contract by the government. The legal system might also want to ensure that a patient is not violating their probation in a drug-related criminal case. In addition to employers seeking to minimize on-the-job risk and the legal system seeking to minimize societal threats, drug rehab facilities are also interested in conducting drug testing. Drug rehab programs could include drug testing on-site or with an outside testing facility hired under contract by the rehab center. These parties have a vested interest in knowing whether a person is drug-free. Additionally, drug testing kits are also available for purchase by general consumers, primarily via various Internet web sites. However, this is an amateur approach with unreliable results. Drug testing is best left in the hands of professionals.