Drug Test FAQ

How Long Does Weed Stay In Your Hair Follicles?
The Definitive Answer

Hair scalp microscopic view

Tetrahydrocannabinol, or THC, is the main chemical found in marijuana.

While marijuana effects wear off in a matter of hours, THC stays in your system for weeks.

How long does marijuana stay in your system exactly depends on a series of factors, as well as the type of drug test you’re subjected to.

If you have to do a hair follicle test, tough luck. The detection time for this test is several months. If you consume cannabis during this period, THC will stay in your body. 

Here’s everything you should know about hair follicle drug tests — from how long THC stays in your hair, to how to avoid testing positive.

How Long Does Weed Stay in Hair?

Woman holding marijuana sachet pointing at her head/hair

Weed can stay in your hair for 90 days. This time frame is calculated based on how long the hair needs to grow past the scalp and the part of the hair used for drug testing.

Hair needs between 5 to 10 days to push past the scalp [1]. Drug testers take hair 1.5 inches from the scalp.

Since hair grows about 0.5 inches per month, it means you need about three months before the THC is out of your hair.

If a drug tester uses the standard 1.5 inches of your hair, and it’s been longer than three months since your last use of weed, you should be fine.

But, let’s imagine your hair is 18 inches long, and a drug tester uses the far ends of the strands. You could test positive for marijuana you had more than three years ago.

Compared to other forms of drug testing, the follicle test is by far the most rigorous. 

Moreover, THC binds to all hair on your body, not only the one on your head. This means body hair can also be used for a drug test.

Note: THC is fat-soluble, so a person’s body fat and metabolism play a significant role in how long weed stays in the body and how much THC is absorbed in the hair.

Marijuana users with more body fat will have a higher amount of THC in the body, so the detection time will be longer as well.

Chronic vs. Occasional Users

How long weed will stay in your system also depends on whether you’re a chronic user, use marijuana for treatment of body injuries or health conditions, or if drug use was a one-off. 

One study stated that chronic users, i.e., people who smoke weed daily, were positive for THC on a drug test 77% of the time [2].

On the other hand, less than half of marijuana users who smoke cannabis once a week tested positive. This means marijuana users who smoke infrequently could luck out, and the test may not show high levels of THC.

How Does Marijuana Get in the Hair? 

A person smoking a jointWhen you take marijuana in any form, you’re releasing its active compounds into your system. 

These metabolites go through your bloodstream to bind themselves to cannabinoid receptors of the cells. Cannabinoids are metabolites of THC, which is what tests can detect in your body.

At the same time, some of the cannabinoids also enter the blood vessels that feed the scalp cells and come to the follicle cells known as hair papilla. As the hair grows past the scalp, it also carries the THC metabolites with it.

This is how weed can stay in your hair and body, and tests can detect THC and the approximate last use of cannabis.

Related Article: Hair Follicle Detox Home Remedy

How Hair Follicle Tests Detect Marijuana

Only a 1.5-inch hair sample is enough to show the presence of THC and make you fail a drug test.

It’s difficult to beat the test because the sample is taken from the root. The hair sample is tested at the follicle to check if there are THC metabolites bonded to it.

Once the hair is collected, it’s washed, chopped up, and put in a solution that breaks it down into components.

The solution goes through the ELISA screen, which is a lab procedure that uses antibodies to bind the THC molecule.

If the test is positive, a secondary test is done on another hair sample – gas chromatography or mass spectrometry. These tests are even more accurate, and if the THC level is above 0.1 picograms, it shows you’ve used marijuana in the past three months.

How Trustworthy are Hair Tests?

A woman's hair roots I’ve talked about how a hair test can detect traces of THC that’s gone from the bloodstream to the hair.

However, THC can get into your hair via physical contact. This means you don’t necessarily need to use marijuana to test positive for it [3].

Here are some cases in which you can test positive even if you haven’t been using marijuana:

  • If you’ve been exposed to secondhand smoke
  • If you’ve touched marijuana
  • If someone who handled marijuana touched your hair

Recently, there’s been a debate about whether hair testing is a good way to decide if the person has been using marijuana or not. This is mostly because of the high chance of a false positive.

One research suggests that a drug test can detect THC, which has been transferred to a non-user through hands, sweat, or exiled smoke [4]

“Even though this testing is frequently used because it’s a lot less invasive compared to a blood or a urine test, it’s known for having high rates of false positives.” – Inverse, YouTube Channel

A 2017 study analyzed hair samples taken from 136 participants. They could detect THC levels in 77% of chronic users and 39% of light users [5].

This shows that chances of having THC detected increase with a higher frequency of marijuana use. The authors concluded that a hair test is unreliable for detecting light cannabis use.

Finally, a Substance Abuse and Mental Health Services Administration report said that people with darker-colored hair are more likely to test positive. In contrast, people with grey-colored hair frequently have false-positive results [6].

How to Pass a Hair Drug Test – 2 Methods

Doctors collecting hair samples

Compared to the urine test, blood tests, and saliva tests, it’s almost impossible to beat a hair test. You certainly won’t avoid weed detection by detoxing.

However, there are a couple of things you can try in order to reduce the risk of detection:

1. Detox Shampoos

There are several detox shampoos out there that can help you pass a hair follicle drug test. I’ll admit, I’m skeptical as to how well these work. 

Yes, the shampoos will wash off the THC from the hair surface. However, they can’t get rid of THC that’s in the hair strands.

That’s why I recommend going for the Macujo method.

2. Macujo Method

Detergent container white backgroundYou’ll need a range of supplies, such as:

  • Shampoo with 3% salicylic acid
  • Liquid detergent
  • White vinegar
  • Shover caps x 10

Once you get them all together, here’s what to do:

  1. Put on the goggles
  2. Wet your hair and put tons of vinegar into it
  3. Massage in the salicylic acid shampoo
  4. Put on the shower car and let everything sit in your hair for up to 40 minutes
  5. Then rinse everything off, and finish with a detergent

Related Article: The Macujo Method Reviews

Pro tip: Make sure to wear goggles, as this can burn your eyes; and wipe any excess vinegar and shampoo from your skin, as you don’t want to show up for a test with irritated skin showing.

Other Ways to Pass a Drug Test

A guy shaving his head by himselfThere are a couple of other things you can do as well:

  • Use Jerry G method — Bleach the hair with peroxide bleach and baking soda, which will destroy the follicles.
  • Shave all your hair — This one is pretty extreme, not to mention highly suspicious.
  • Buy a home test kit — Check if you pass urine tests or other tests on your own after a detox.

Recommended Articles:

How Long Does Marijuana Actually Stay in Your Hair Follicles

How long will marijuana stay in your system depends on several factors, such as the percent of body fat and fatty tissues, and if you fall under chronic cannabis users or occasional users.

In general, compared to other drug and alcohol substances, marijuana will stay in your system for a longer length of time, which means the detection window is longer as well.

If you know some cannabis users suffering from marijuana abuse and in need of recovery, try to help them get adequate health treatment. Just like with drug and alcohol recovery, cannabis recovery takes time and medical assistance, but the right treatment can help them.

If your goal is to pass the hair drug tests, wait for 90 days as this length of time is required to avoid detection; or use one of the methods I mentioned above to increase your chances of passing and getting negative test results.


References:

  1. https://www.questdiagnostics.com/dms/Documents/Other/hair_testing_faq.pdf 
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396143/ 
  3. https://www.nature.com/articles/srep14906
  4. https://www.nature.com/articles/srep14906 
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396143/ 
  6. https://www.samhsa.gov/sites/default/files/meeting/documents/july_2013_bourland.pdf

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