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How to Pass Your Next Screening | PotGuide.com



According to Quest Diagnostics, a national leader in drug testing services, positive drug test rates are at an all-time high. Last year, positive tests across the whole U.S. workforce increased nearly 4%, and are up over 12% from 2016. Since 2012, positive tests for cannabis use have surged over twice as much in states where it has been legalized, and over 60% in states with medical programs. And in states where all cannabis use remains illegal, positive test rates still rose by 58%.

These numbers tell the story of a society reversing its attitude toward marijuana, and even embracing it as a natural way to relax and recover. Yet despite Americans’ support for access to cannabis, and an ongoing wave of legalization, many employers still discriminate against cannabis users with drug tests, including urine and hair tests.

Of the two, the hair follicle test looms as the inescapable, untrickable test of tests. Here’s what cannabis users should know about what these tests are, how they work, and what they learn about you.

What is a Hair Follicle Test?

A hair follicle test analyzes the biological makeup of your hair for residues called metabolites, the “stuff” left over when your body metabolizes certain chemical compounds. The test can easily detect THCA, along with several other drugs such as:

  • Amphetamines (incl. Meth and MDMA)
  • Cocaine
  • PCP
  • Opioids (incl. prescriptions and synthetics)

What makes this test particularly punishing for cannabis users is how sensitive the instruments are to THC. Drugs are detected down to the picogram – that is 0.000000000001 grams – per milligram of hair. The confirmatory level for PCP is 300 pg/mg. Opiates are detected at 500 pg/mg. THCA metabolites can be confirmed at only 0.1 pg/mg.

A hair test is designed to detect regular, habitual use over the previous 90 days, so here’s the bad news: if you’ve been using cannabis regularly over that period, it will almost certainly be detected. Of course, hope springs eternal, and never say never, but get comfortable with the idea that you will never slip one by this test.

The hair follicle test is an immunoassay, a biochemical test that uses antibodies to identify specific molecules in a more complex mixture. If there are any receptive molecules, the antibody will bind to them, alerting the system to the presence of a given substance – in this case, THC metabolites. Immunoassays were developed in the 1950s by Rosalyn Sussman Yalow, whose efforts were rewarded with a Nobel Prize. Then, science spent seven decades refining it.

Nevertheless, here’s the good news: drugs cannot be detected in hair until about a week after consumption (urinalysis is used to test the most recent 7-10 days). You could smoke your face off the night before the test and pass with honors. And it can only detect habitual use, so if you only smoked at a few parties, you might be fine. 

How do Hair Tests Work?

A hair test is less like a urinalysis (urine test) and more like giving blood. Patients simply sit patiently while a nurse uses scissors to cut approximately 100 hairs from the crown of the head. Of these, the first 1.5 inches will be analyzed. Hair grows from our heads at an average rate of 0.5 inches per month, so the most recent 1.5 inches provides a 90-day window into the past.

If you don’t have any hair on your head, or don’t feel comfortable parting with any, then body hair can be used instead (in order of procedural preference: chest, underarm, leg, then facial hair). Though, because body hair tends to grow more slowly, 1.5 inches of that can provide an even further look back.

Blonde Hair

While body hair is accepted, we recommend sticking to hair from your head, as it won’t show as far back. photo credit

It is called a “follicle” test not because it tests the follicle of the hair, but rather it tests the hair for evidence of cannabinoids that would have originated in the follicle (which, ipso facto, could only get there from the bloodstream). Before they can be metabolized by the body, some cannabinoids collect in the capillaries and tissue around hair follicles. There, they become integrated with the hair cells and rise from the scalp as the hair grows. And there’s the rub: once a cannabinoid like THC is in your hair, it’s part of your hair. There’s no getting it out or hiding it from a test any more than you could hide color from a stylist.

To ensure accuracy and eliminate bias, collection and shipment of the hair samples follow a strict chain of custody. Any sample even a step outside of this regimen will be rejected. That doesn’t mean you pass, it just means they’ll test you again. Samples are usually shipped overnight to a central laboratory, where they are washed free of any external contaminants.

The test actually occurs across two stages. The first is called an Enzyme-linked Immunosorbent Assay, or ELISA. ELISA uses an antibody that binds with certain molecules, essentially highlighting them. Similar procedures are used in antibody tests and blood bank analyses. Negative ELISA tests are not looked at again, and the results are released in about 24 hours.

An ELISTA test

The ELISA test is the first step in identifying THC from a hair follicle. photo credit

If ELISA finds something, then the sample undergoes a second test, called Gas Spectrometry/Mass Spectrometry (GS/MS). And many tests now employ tandem spectrometry, effectively doubling the sensitivity of the test. While ELISA detects that a drug is present, mass spectrometry detects which drug is present – and can separately identify hemp and poppy seeds, thank you very much. Gas spectrometry produces a “molecular fingerprint” that will identify the drug at the molecular level. No hiding color from a stylist.

This entire process is usually complete within 72 hours. Remember to let the nurse or administrator of your test know if you are taking any prescription medications that you’re concerned may result in a false positive.


Many still claim that excessively bleaching or dying your hair can fool these tests, and someone’s cousin somewhere may have flown under the radar once, but in general, these tests are a point of pride in medical science, and we rely on them for procedures as critical as blood transfusions.

Some products claim to purge your hair, or at least coat it with something that will fool or confuse the test. Even if that doesn’t look suspicious, at best you’ll only be asked to give another sample, probably from your body. Curious consumers can purchase test kits online, but expect a lab fee and a little patience, as the sample will need to be mailed away.

The best and only way to be sure of passing a hair test is to abstain of THC for 100 days.

What are your thoughts on hair follicle tests for cannabis? Share in the comments!

Photo Credit: allanswart (license)


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