Table of Contents
Key Points
- THC is an acronym for tetrahydrocannabinol, the psychoactive component in cannabis products.
- THC is absorbed in the bloodstream and binds itself to hair follicles.
- Factors that impact how long THC will be detected in your hair include frequency of use, metabolism, hair health, and hair color.
- THC can stay in your hair on average for up to 90 days.
While cannabis usage has become less stigmatized in recent years, many users are unaware that THC (tetrahydrocannabinol) can stay in your system long after consumption. While saliva, urine, and blood tests are commonly used to detect THC, hair follicle tests provide a long-term detection window.
This can make hair follicle THC tests a preferred method for employment screenings, legal cases, and some drug rehabilitation programs.
Knowing how long THC can stay in your hair may help you decide whether or not to consume cannabis products. It is also a consideration when determining how long it will take to detox THC from your system.
What Is THC?
THC, also known as tetrahydrocannabinol, is the primary psychoactive component in cannabis [1] responsible for altering normal states of consciousness or creating the “high” experienced when taking cannabis or cannabis-based products.
It interacts with the brain’s CB1 receptors, impacting cognitive functions, memory, and pleasure. THC is consumed through smoking, vaping, edibles, tinctures, and topicals, with each method affecting absorption and metabolism differently.
How is THC Metabolized and Stored in Hair?
Whether you’re a seasoned smoker, a first-time user, or simply curious about the topic, understanding how THC is metabolized and its relationship to hair growth is essential.
To better understand how and why THC appears in your hair, you must first know how the body metabolizes THC
As THC is absorbed in your bloodstream [2], a chain reaction occurs in the body’s endocannabinoid system. This system affects different organs and systems, including the heart, lungs, liver, brain, vascular system, and muscles.
THC is metabolized by the liver into various fat-soluble metabolites, including THC-COOH. These metabolites can be stored in fat cells and remain in the body for extended periods. THC reaches the hair follicle through the bloodstream, where it binds to melanin (the pigment in hair). Once stored in hair shafts, THC remains detectable for up to 90 days—or even longer in body hair.
How Long Does THC Stay In Your Hair?
On average, THC can be detected on hair samples for up to 90 days after the last consumption of cannabis-based products. This is significantly longer that other THC tests including urine, saliva, and blood tests. THC can even remain in body hair for up to 12 months.
| Test Type | Detection Window |
|---|---|
| Urine Test | 3–30 days, depending on use frequency |
| Saliva Test | 24–48 hours |
| Blood Test | A few hours to 2 days |
| Hair Test | 7–90 days (up to 12 months for body hair) |
Factors That Impact How Long THC Stays In Your Hair
Frequency of Use
How often you consume cannabis and the amount will impact how long THC stays in your system and how long it will stay in your hair.
- One-time users: THC may only be detectable for a week to a month.
- Occasional users (2–4 times a month): THC can remain for up to 90 days.
- Chronic users: THC builds up in the system and can be detected for even longer than 90 days.
Metabolism
Your metabolism is a primary factor in how quickly THC can be absorbed and removed from your body. Everyone’s metabolism is different, and the speed at which your body can process any type of substance might be very different from one person to the next.
- A fast metabolism clears THC out of your system quicker, reducing the amount stored in hair.
- THC is fat-soluble, meaning higher body fat leads to prolonged detection
Hair Health
People may not think their hair health impacts how long THC stays in their hair, but it does. Healthy hair is better at retaining metabolites than unhealthy or damaged hair. This is because THC is stored in the hair’s cortex and can be detected until the hair is shed or cut.
Hair Color and Type
Surprisingly, the color of your hair can also affect how long you can detect THC in hair follicles. THC is easier to detect in darker hair colors like black and brown. This is because melanin, the pigment found in darker hair colors, helps act as a binding agent for THC. Curly or coarse hair may may also store more THC than straight hair.
As a result, individuals with lighter hair colors will typically see a shorter detection window than those with darker hair.
Hair Length and Growth Rate
A standard THC hair test will analyze the 1.5 inches closest to the scalp, equating to three months of history. With the average rate of hair growth being 0.5 inches per month, the rate at which your hair grows will impact how long THC may show up in a hair follicle text.
Hair Treatments or Second Hand Smoke
Bleaching, dyeing, and perming can reduce detectable levels of THC in hair, but do not eliminate it completely. Environmental contamination (e.g., secondhand smoke) does not usually cause a positive result due to washing protocols before testing. So hanging out with someone smoking before you THC hair follicle test should not change the outcome.
Hair Follicle Drug Test Process
A hair follicle drug test follows these steps:
- Sample Collection: A small hair sample is cut near the scalp (or from body hair if head hair is unavailable).
- Initial Screening: The sample undergoes an enzyme-linked immunosorbent assay (ELISA) to detect drug metabolites.
- Confirmatory Testing: If positive, the sample is re-tested using gas chromatography-mass spectrometry (GC-MS) to rule out false positives.
THC Hair Follicle Test results are usually available within 2-3 weeks.
The following cutoffs are commonly used to determine if re-testing is needed[4]:
| Test Type | Cutoff Levels (ng/mg) |
| Initial THC Test | 0.1 |
| Confirmatory Test (THC-COOH) | 0.0002 |
Hair Follicle Tests vs. Other Drug Tests
Hair follicle tests have several advantages over urine and saliva tests:
- Detects long-term use by providing up to 90 days of drug history.
- They are harder to “cheat” as unlike urine tests, hair samples cannot easily be substituted.
- Hair test for weed are slightly more reliable for chronic use detection, however there is evidence to suggest they still struggle to pick up light cannabis consumption[3].
There is also evidence to suggest that hair follicule tests for cannabis can result in a positive test for those who only handled the product with frequency, which would include workers at legal marijuana farms[5].
How to Pass a Hair Follicle Drug Test
The only way to ensure you pass a hair follicle drug test for cannabis use is to stop using cannabis at least 90 days before the test which will ensure that all THC is detoxed from your system.
Final Thoughts
Hair follicle drug tests provide the most extensive detection window for THC, making them a common choice for workplace screenings and legal cases. While THC can stay in your hair for up to 90 days, several factors influence how long it remains detectable. Understanding these factors and testing procedures can help you make informed decisions about cannabis use and drug testing policies.
Frequently Asked Questions
Below are some of the most frequently asked questions regarding THC & Hair Follicle Tests
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