Questions and Answers About Hair Testing

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How far does it go back?

Hair testing generally uses 1-1/2 inches of hair, representing about 3 months’ growth (head hair normally grows at about 1/2 inch per month). It is generally accepted that in order to test positive, the drug in question must have been used 3 times or more within the window of the test. After a drug is used, it takes about 7-10 days for the hair containing the drug to grow out of the scalp enough to be cut. Therefore, the hair test will not include drugs used in the week prior to the test. The drug remains in the hair, growing out much the same as hair dye and "dark roots". Eventually that hair containing the drug is cut off with normal haircuts.

Do medications interfere?

There are some prescriptions that contain the same drugs that are commonly found "on the street". There is no easy way to distinguish between the two forms of the drug. However, the problem is not as big as it would seem.

There are no prescriptions for PCP or cocaine. It is extremely rare to find cocaine used in a medical setting, although it happens occasionally, usually to control bleeding from the eye or nose. If used, it will be well documented in the person’s medical file. Such use would cause the urine to test positive for cocaine metabolite for a few days, but would not be sufficient to cause a positive hair test.

Heroin is rarely prescribed in the United States, but again would be well documented. It appears that poppy seeds do not interfere in hair testing. Other prescribed opiates may occasionally cause a positive screen, but are sorted out in a confirmation test.

There are some prescription diet pills that contain either amphetamine or methamphetamine, as well as a drug for Parkinson’s Disease that is a form of methamphetamine. Some doctors prescribe amphetamines for ADHD. Ecstasy is included in the amphetamine class of drugs, and is identified at confirmation.

What is "confirmation"?

Because there are substances that interfere with screening, causing "false" positive results on screening, the positive screen must be confirmed. The accepted, state-of-the-art method is called GC/MS, gas chromatography/mass spectometry. Each drug peak comes off the GC at a specific time (retention time), and with specific ion ratios, allowing it to be separated or distinguished from similar substances. To be called positive, the peak in the sample must match a known pure standard of the drug in question in both retention time and ion ratios. In addition, the presence of metabolites may be checked. For instance, amphetamine is the major metabolite (what the body turns it into) of methamphetamine. So, If there’s been methamphetamine use, the hair should contain the methamphetamine AND amphetamine. Likewise cocaine. Cocaine users will show positive for cocaine AND the metabolite, benzoylecgonine. Finding the parent drug without the metabolite for these drugs is suspicious, and needs to be investigated.

What if I’m in a room with someone who is using drugs?

Since it takes multiple uses to test positive, and metabolites are checked when possible, it is pretty much impossible to test positive form passive exposure on a limited basis. Extreme passive exposure may result in very low levels.

What if I bleach and/or dye my hair? Can I get rid of the drugs?

No. The drugs are IN the hair, not ON it. Drugs are actually incorporated into the hair shaft from the bloodstream. Severe chemical washing and bleaching removes drugs on the hair, and may, in some cases, lower the level in the hair slightly, but it will not remove the drug completely. As a matter of fact, before we do our confirmatory testing, we wash the hair and test the washes to make sure all the drug is off the outside of the hair before we continue, so that we are assured that any drug we find is from within the hair. Hair coloring has no effect on the testing.

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For more information on hair testing, call us at 1-800-989-1206