What is a hair follicle test?

November 12, 2012

What is a hair follicle test?

Hair samples can be taken to test for drugs as long as the main hair follicle is included in the sample.

A hair follicle test is a drug test – a small sample of hair is taken and used to identify specific drugs which may or may not have been ingested by the owner. Drug use is identified by the presence of metabolites from the drugs in question within the follicle. Carrying out a hair follicle test is both easy and accurate and in some cases is also more accurate than urine tests in detecting long term, low level use of some drugs including PCP, opiates and methamphetamine. Hair follicle testing has a wide detection range which is why it is popular as a method of drug testing in the work place as well as elsewhere.

Drugs in the hair

As it grows, hair is nourished by blood, this means that any drugs taken – whether orally, injected, smoked or sniffed – will enter the hair via the bloodstream and become embedded in the hair shaft. Although small traces of the drugs will slowly leave the hair, as a result of hair washing and styling, some of the drug will remain trapped in the within each strand meaning it is impossible to avoid drug use detection. Around a week after the drug was ingested the affected hair will have grown above the scalp – clearly this means that very recent drug use may not be detected and if it is suspected then a urine test should be carried out. If the hair on the head of the individual is too short for testing then any body hair can be used.


Hair follicle tests are all more or less the same. A sample of hair – from any part of the body, is required, this needs to be hair that is at least ½ an inch long and with around 100-120 strands. Since hair grows at the rate of ½ an inch per month each of those ½ inches will give a 30 day drug history – so, for example, the hair sample is 11/2 inches long then a 90 day drug use history will be found. Hair follicle drug tests are often the test of choice, despite being more expensive than other tests, simply because they are so accurate and, in addition, are much easier and less embarrassing to administer than a urine test for example. It also provides a longer window than other tests – a urine or saliva sample can only provide evidence of drug use in the previous couple of weeks.

Which drugs?

There use of a number of drugs can be identified with the use of a standard hair follicle test. These include -

  • Cocaine

  • Marijuana

  • Methamphetamine

  • Ecstasy

  • Opiates

  • PCP

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