How Accurate Is Hair Follicle Testing?

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  • Written By: N. Madison
  • Edited By: Jenn Walker
  • Last Modified Date: 26 March 2014
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Hair follicle testing is said to be extremely accurate for detecting lower levels of drug use as well as drug use over a longer period of time. For example, there are some drugs that may be difficult to detect in a person’s urine once several days have passed. Hair follicle drug testing, however, may detect drug use that occurred weeks, or even months, before the person was tested. Drug test detection times may depend on the type of drug that was used, the frequency with which it was used, and the metabolism of the person who is being tested. Usually, however, hair follicle testing is accurate for much longer than a drug or urine test.

Often, hair follicle testing is considered the optimal test of choice because it is highly accurate and provides extended drug-use detection times. While drug detection times do vary, urine and blood detection times often amount to only days. For example, marijuana use may only be detectable in the urine for up to about 63 days in a person who has used it daily. A hair follicle test, however, could produce accurate results for up to three to six months. In most cases, a 90-day detection time is considered standard for hair follicle testing, however.


It is the length of a person’s hair sample that limits how far back a follicle test can detect drug use. A 90-day detection is considered normal, since drug use can be detected back this far even when the hair is short. For example, as little as 1.5 inches (about 3.81 centimeters) of hair is required for the 90-day detection of a wide range of drugs. If the hair available for testing is much longer, however, a drug test may reveal accurate results for a much longer period of time. It could, for instance, reveal drug use that occurred several months before the testing.

One of the reasons hair follicle drug testing is considered so accurate is that it would be very difficult for someone to detox his hair and fool a follicle test. There are some companies that sell special shampoos, teas, and other products they claim are helpful for beating hair follicle tests. These products do not usually work, however. Even cutting off all of the hair on one's head is unlikely to work for blocking drug detection. Hair for drug testing can be taken from other parts of the body; pubic hair isn’t usually used for drug testing, however.


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Post 5

Are the interactions of other drugs able to affect the results? A friend was told he tested positive 90 days prior. The only problem is he had open heart surgery and supplied 31 pages of drugs given in the three weeks he was in hospital. I'm sure he wasn't using in the hospital, but they maintain that wouldn't affect accuracy.

Post 4

Wow. The same thing just happened to my sister. She's been clean and sober for almost a year and the courts ordered the hair follicle and it was positive. That test is crap.

Post 3

I am one year clean and sober and my hair follicle test came back positive, as well.

Post 2

Sounds like your husband isn't telling you something.

Post 1

My husband has been clean for over four months and yet his hair follicle test for "90 days" came back positive and he has lost his job because of it. That is not fair. They had to have tested it back further than 90 days and now what?

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