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THC in Hair Sample

Published: December 19, 2013
Dear TeenHealthFX,


I used marijuana about 7 or 8 times over a period of six months, but I have been clean since June 2009 and have no intentions to do drugs again. It takes about a week or two to get out of my system (I know because I've bought drug tests and tested myself a couple times), so I could pass a urine test now, but I've heard that THC stays in your hair. This concerns me because my hair is long (way past shoulder length), and I don't see a drastic haircut in my near future. I do however get a trim every couple months. If I somehow get in a situation in which I have to take a hair test and the THC hasn't grown out, would I fail it?

Signed: THC in Hair Sample

Dear THC in Hair Sample,


When using a hair sample to test for drugs the laboratory usually only uses the first 1.5” of hair from the root end. If a longer sample is sent, the laboratory usually cuts the hair to 1.5” when performing the test. So getting a haircut would not alter the outcome of the test. Even if the person being tested is bald or has a shaved head (perhaps in preparation for the test) this will not give them an advantage. Hair can also be taken from almost any other area of the body, including facial hair, the underarms, arms, and legs. Hair testing is the most accurate in determining drug use between 5 and 90 days previous to drug use, but often misses drug use immediately previous to testing, since the THC has yet to be absorbed in hair growth.

Hair testing is becoming more reliable as technology advances, and there is no known way to sanitize a hair specimen in order to falsify the results of the test, despite what some retailers advertise.

If you have to take a drug screening through hair analysis and have used marijuana in the past 90 days then there is good possibility that you will test positive. Cutting, shaving or over the counter products will not alter this fact. The only way you can guarantee that you will come up clean is to stay clean.

If you feel like you have a problem with marijuana then it would be a good idea to seek help. You may want to check out Marijuana Anonymous for some good information and resources within your area


Signed: TeenHealthFX