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How Accurate is Hair Follicle Testing?

Nicole Madison
By
Updated Mar 03, 2024
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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 follicle test, however, can 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.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Nicole Madison
By Nicole Madison
Nicole Madison's love for learning inspires her work as a The Health Board writer, where she focuses on topics like homeschooling, parenting, health, science, and business. Her passion for knowledge is evident in the well-researched and informative articles she authors. As a mother of four, Nicole balances work with quality family time activities such as reading, camping, and beach trips.
Discussion Comments
By anon996052 — On Jul 02, 2016

Has anyone ever been suspected of altering their hair for the test? If so, what was done to confirm?

By Robfife — On Jun 09, 2014

My suggestion for questionable false positives given by one specific laboratory, is to ask to review their positive and negative controls to see if they react the way they are supposed to, in positive and negative lab control specimens, separate from the patient's specimen and then possibly review the chain of command protocol and signatures to ascertain the specimen has been secured properly from cross contamination during collection and then have the first lab retrieve the stored patient specimen and submit it safely to a second reputable U.S. lab, licensed by ASCCP independent for testing, to test for the specific drug in question.

If a second test comes back negative, contrary to the first test being positive, then you have a case for defamation of character, and a civil case for damages in superior court, and might be entitled to punitive relief. This information is only provided to see if you might need to contact a lawyer for proper legal action. I am not a lawyer, but have worked in a laboratory and with lawyers as an expert witness in the past in matters of law.

By anon955733 — On Jun 09, 2014

My suggestion for questionable false positives given by one specific laboratory, is to ask to review their positive and negative controls to see if they react the way they are suppose to positive and negative, separate from the sample specimen and then possibly submit a sample to another independent lab, to test the specimen sample. If second test comes back negative contrary to the first test positive, then you have a case for defamation of character, and a civil case for damages, in superior court, and might be entitled to punitive relief. This information is only provided to see if you might need to contact a lawyer for proper legal action. I am not a lawyer.

By anon936285 — On Feb 28, 2014

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.

By anon354951 — On Nov 12, 2013

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.

By anon335708 — On May 22, 2013

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

By anon330966 — On Apr 19, 2013

Sounds like your husband isn't telling you something.

By anon134280 — On Dec 14, 2010

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?

Nicole Madison
Nicole Madison
Nicole Madison's love for learning inspires her work as a The Health Board writer, where she focuses on topics like...
Learn more
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