Drug testing involves checking for substance use in people who do not necessarily have any symptoms of intoxication or a substance-related disorder Substance-Related Disorders . It may be done systematically or randomly in
Certain groups of people, such as students, athletes, and prisoners
People who are applying for or who already hold certain types of jobs (such as pilots or commercial truck drivers)
People who have been involved in motor vehicle or boating accidents or accidents at work
People who have attempted suicide by unclear means
People in a court-ordered treatment program for drug abuse or with terms of probation or parole requiring abstinence—to monitor compliance
People in a substance abuse treatment program—to detect continuing substance abuse and thus better plan treatment
People required to undergo drug testing as part of custody or parental rights hearings
Members of the military
Typically, people have to give consent for drug testing except in certain circumstances, such as car or workplace accidents. Drug testing cannot determine how often a substance is used and thus cannot distinguish casual users from habitual users. Also, drug testing targets only some substances and thus misses many others. Substances most commonly targeted include
A sample of urine, blood, breath, saliva, sweat, or hair may be tested. Urine testing is most common because it is noninvasive, quick, and able to detect many drugs. It can detect drugs that were used within 1 to 4 days, sometimes longer, depending on the drug used. Blood testing is rarely done because it is invasive and can only detect drugs up to a few hours after use. Hair testing is not as widely available but can detect some drugs if they were used in the previous 100 days. Health care practitioners may directly observe the collection of the sample and seal it so that they can be sure the sample has not been tampered with.
Drug tests are not always accurate. The most commonly used urine tests give incomplete and sometimes incorrect results. Sometimes, the tests do not detect a drug the person is actually using (false-negative result). This can happen if the test is not designed or has limited sensitivity to detect a particular drug, if the urine is very dilute so that the amount of the drug in urine is less than what the test can detect, or if the person adds a substance to the urine to alter the sample or submits a sample from someone else. On the other hand, the tests sometimes are positive when the person is not actually using drugs (false-positive result). For instance, poppy seeds can produce false-positive results for opioids (heroin is derived from poppy plants).