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How Does Hair Drug Testing Work?

What is Hair Drug Testing?

Hair drug testing is a method of screening for drug usage. A sample of a person’s hair is taken from their head or body and is dispatched to a laboratory for analysis in order to detect use of drugs of abuse.

What time period does hair testing cover?

Normally we will ask for a 40mm sample of hair for analysis. As human head hair grows on average at a rate of 13mm per month, this means that a typical drug hair test will cover a time period of around 90 days. This time frame is just an estimate as speed of hair growth can vary from individual to individual.

Does body hair give similar results to head hair?

Some donors may not have enough head hair to provide a sample for drug testing. In this case, body hair can be used instead. The time frame of drug usage represented by body hair is harder to ascertain than for head hair due to the high variability of body hair growth rates.

How soon after use can a drug be detected in hair?

Normally it will take 5-10 days for the hair to grow to a sufficient length above the scalp so that it can be collected and drug use identified.

Can environmental exposure to drugs (cannabis smoke, crack smoke, etc.) have an effect on the hair test results?

No. A wash procedure is used before the sample is analysed. Also, a hair drug test will look for the parent drug and its metabolite (bi-product). For cannabis analysis, only the metabolite is detected (THC-COOH). This metabolite cannot be picked up from smoke or other environmental factors as it is only produced by the body.

How can you beat a hair drug test?

You can’t cheat a drug test that uses hair. At the present time we know of no successful commercial adulterants that could affect hair drug test results. Use of normal hair care products (shampoos, hair dyes, bleach, etc) does not have any significant effect of hair drug test results.

Does hair colour effect hair drug test results?

The colour of your hair is determined by the amount of melanin it contains. Many, well documented studies have shown that hair colour does not have a significant effect on drug test results.

Can hair collected from a brush be used?

It can but the laboratory would have to identify the sample as having come from an anonymous donor, meaning that the sample could not be attributed to any one person and the time frame of drug usage could also not be stipulated.


Photo by Tim Mossholder on Unsplash

Zoom Testing is a leading UK drug testing company and a supplier of Drug Test Kits.

This post was originally published in 2014 and has been updated since.


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