The hair follicle test is said to be extremely accurate in detecting lower levels of drug use as well as drug use over a longer period of time. For example, there are some drugs that can be difficult to detect in a person's urine after several days have passed. However, hair follicle drug tests can detect drug use that occurred weeks or even months before the person was tested. Drug test detection times can depend on the type of drug that was used, how often it was used, and the metabolism of the person being tested. In general, however, the hair follicle test is accurate for much longer than a drug or urine test.
Hair follicle testing is often considered the optimal test of choice because it is highly accurate and provides long drug use screening times. While drug detection times vary, urine and blood detection times often amount to just days. For example, marijuana use can only be detected in the urine for about 63 days in a person who has used it daily. However, a hair follicle test could produce accurate results for up to three to six months. However, in most cases, a detection time of 90 days is considered standard for hair follicle testing.
It is the length of a person's hair sample that limits how far back a follicle test can detect drug use. A detection of 90 days is considered normal, since drug use can be detected so far, even when the hair is short. For example, as little as 1.5 inches (approximately 3.81 centimeters) of hair is required for 90-day screening of a wide range of drugs. However, if the hair available for testing is much longer, a drug test can reveal accurate results over a much longer period of time. It could, for example, reveal drug use that occurred several months before the test.
One of the reasons drug tests on hair follicles are considered so accurate is that it would be very difficult for someone to detox their hair and fool a follicular test. There are some companies that sell special shampoos, teas, and other products that claim to be helpful in beating hair follicle tests. However, these products usually do not work. Even cutting off all the hair on your head is unlikely to work to block drug detection. Hair for drug testing can be taken from other parts of the body; However, pubic hair is not generally used for drug testing.