How Detectable is THC in Hair?

A woman in a black jacket with shoulder-length blond hair.

THC hair follicle tests can sometimes be requested when you apply for a job or randomly once you have already been hired. If you smoked a few weeks ago or regularly use cannabis for medicinal purposes, you might be wondering if the THC will show up in your hair. Here are a few facts about THC and hair follicle testing to help you plan the best approach to THC hair detox.

What is a THC Hair Follicle Test?

When you or a third party want to detect a pattern of repeated drug use, a hair follicle test may be requested rather than a urine, saliva, or blood test. This is because THC in hair can be detected for up to 90 days after cannabis use as opposed to the days or weeks that it can be detected in your urine.

THC shows up in your hair in two main ways:

  1. Blood cells containing THC-COOH or “carboxy THC” form part of new strands of hair that grow after the date of cannabis use. Carboxy THC is the metabolite that your body produces in response to THC.
  2. THC-COOH excreted by the sweat and sebum glands at the base of your hair follicles causes existing strands to test positive for THC.

As the rate of hair growth varies from one person to another, the levels of THC in your hair may decrease at a faster or slower rate than average. However, a 2007 study indicates that levels may drop below detection much faster in non-daily users (with 52% testing positive) compared with daily users (85% positive).

How Does the Hair Follicle Test Work?

scissors cutting hair for a THC in hair test

To detect THC in your hair, a sample of 100-120 strands of hair is cut with scissors from several places on your head to avoid creating bald patches. If you have very little hair, body hair can be used for the test instead. This sample is sealed in a secure packet and sent to the laboratory where it will be washed for environmental contaminants and analyzed. Hair dyes, shampoos, and styling products do not affect the results.

In most cases, two tests—ELISA and GC/MS—will be used to detect up to 17 different drugs while ruling out a false positive from having only eaten poppy or hemp seeds. The results will be delivered confidentially and shared with a third party (such as your employer) with your consent.

Can a THC Hair Detox Help Me Pass the Test?

Because of the nature of hair, it is impossible to clear the THC in hair completely, until the bloodstream has been cleared as well. However, three actions can help detectable levels to drop more quickly:

  • Reduce the frequency of cannabis use months in advance of the test (if possible).
  • Cease all cannabis use at least three months before the test (if possible).
  • Follow our suggested detox tips.
  • Cutaway all hair that was present during cannabis usage period.

You can learn more by reading our detox facts and contact our team for personalized assistance.

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