A feature on the New York Times hails the advantage of using hair samples as opposed to urine samples during drug testing.
The title says it all: the hair cannot lie -- at least as far as drug testing is concerned.
Since the 1980s, a drug test has been a standard part of the job application process, as well as the process of staying employed. More than just that, it has crept into many other standard practices not just in the United States but the rest of the world; there are countries that incorporate drug testing into several application processes, such as that of applying for a driver's license.
According to the New York Times article, the practice of workplace drug testing has reportedly led to a decline in the number of people who test positive for drug use over the years. But then again, that may be due to the fact that people can generally prepare for such tests. What that basically means is that a decline in positive results may not necessarily mean a decline in drug use among employees in general.
The usual method that is employed in testing for drug use is the submission of urine samples. Although this method has already led to the identification of drug use, the testing involved in urine specimens only have the ability to detect a single instance of drug use in the prior one to three days. This limitation of the procedure provides a window of opportunity for drug users to cheat the system by physically preparing themselves for a test; they can simply temporarily lay off the habit for a moment just enough to be able to test negative and then go on their old merry way, at least until the next wave of tests.
Hair samples, on the other hand, hold much more information. Hair testing can detect a pattern of repetitive use over a period of up to 90 days, which means a spur-of-the-moment resolution is out of the question and will not be able to yield favorable results.