Hair Drug Test FAQ

Updated February 21, 2017

One of the most common things for companies to do is a mandatory drug test for potential new employees. This drug test can take many forms including hair, blood, saliva, and urine tests. While a the majority of these tests will most likely find drugs that have been recently taken, a hair test can be used to find drugs which have been ingested further in the past. Because of this, many companies are using this type of drug test to monitor their employees.

What is a hair follicle test?

This type of drug test consists of using a small sample of a subject's hair follicle to determine if there are any drug molecules. As you use drugs, they are processed by your system and enter the blood stream. They spread throughout the bloodstream and a trace amount of them ends up in the hair follicles.

What drugs does this test for?

This test is used to primarily screen for cocaine, marijuana, opiates like codeine or morphine, amphetamines (including ecstasy) and phencyclidine (PCP). Further examination of a hair follicle can be done to determine if a subject has ingested any alcohol, heavy metals, poisons or antidepressants.

What is the time period this test covers?

Even though the hair test can discover drug use further in the past than other kinds of tests, it has a limit to that time frame. Usually, a hair test can be used to determine if a subject has done any drugs in the previous 90-day period. Also, for a positive result to show, the drug in question must be used at least three times in that period. This can be extremely helpful in determining habitual drug use. Also, since it takes time for the hair to grow out, any drugs used in the week prior to the test will not show up on the results.

False Positives

Sometimes, a person would try to use the reason of having a prescription which affected the test results in lieu of a positive test. In the case of a hair test, this reasoning no longer is effective. First of all, while cocaine and heroin can be prescribed in extreme circumstances, the patient will have documentation regarding the treatment and there it will not be used in a large enough dose to cause a positive result. Also, while poppy seeds may have caused false positives in tests used in the past, they rarely do in a hair test. Finally, if you are taking diet pills, you may get a false positive, but the test is able to tell whether the amphetamine is from a diet pill or drug.

What kind of hair is used?

Hair from any part of your body can be used; however, hair from your head is the preferred. The rate of growth in your head hair is about ½" in 90 days which helps to show more recent drug use. Bodily hair generally takes up to a year to regrow which would show drug use at some point over the previous year. The 90 day time frame is better to establish regular drug use.

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About the Author

R.L. Cultrona is a San Diego native and a graduate of San Diego State University. She holds a Bachelor of Arts in theater, television and film with a minor in communications and political science. She began writing online instructional articles in June 2009.