How long thc stay in hair
How Long THC Stays in Hair and What It Means for Testing
How long THC stays in hair depends on hair length and usage frequency, typically up to 90 days or more. Hair tests detect THC metabolites embedded in the hair shaft, providing a long detection window. AMH Nationwide processes hair drug tests through five national labs with certified Medical Review Officer oversight. Call (877) 731-6362 for test scheduling.
How long does THC stay in hair?
THC stays in hair for approximately 90 days, though this period can vary based on hair length and individual factors. Hair drug testing detects THC metabolites deposited in the hair shaft from bloodstream exposure after consumption. Because hair grows about half an inch per month, a 1.5-inch sample typically reflects a 90-day drug history.
Factors such as hair color, cosmetic treatments, and frequency of use may influence detection, but generally, hair testing offers one of the longest detection windows for THC compared to urine or blood tests.
AMH Nationwide routes hair samples through five national lab networks: Quest Diagnostics, LabCorp, Omega Labs, United States Drug Testing Labs, and ExperTox, ensuring high-quality analysis and Medical Review Officer review.
How is THC detected in hair samples?
THC is detected in hair samples by identifying its metabolites, primarily THC-COOH, which are deposited into the hair shaft via the bloodstream after cannabis use. The collected hair sample is sent to one of AMH’s partner labs, where advanced analytical techniques such as gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS) are used for precise measurement.
Every non-negative result undergoes review by a certified Medical Review Officer to confirm accuracy and rule out potential confounding factors.
This process helps ensure reliable detection of THC use over the prior 90 days or longer, depending on hair length.
Can a single use of cannabis show up in a hair test?
Yes, a single use of cannabis can be detected in a hair test, but detection sensitivity depends on the amount consumed and individual metabolism. Hair tests are designed to detect repeated or chronic use, but even occasional use can leave metabolites in the hair shaft.
However, very low-level or passive exposure is less likely to produce a positive result because labs apply strict cutoff thresholds to reduce false positives.
AMH Nationwide’s partner labs strictly adhere to SAMHSA and CAP guidelines to maintain test accuracy and reliability.
Are there factors that affect how long THC stays in hair?
Several factors can influence the detection window and concentration of THC metabolites in hair samples. These include hair color, cosmetic treatments like bleaching or dyeing, hair texture, and individual metabolic differences.
For example, darker hair may bind more THC metabolites due to higher melanin content, potentially leading to higher concentrations detected. Chemical treatments can degrade or reduce detectable metabolites, possibly affecting results.
Schedule a Hair THC Test Today
To arrange hair drug testing or get detailed information on detection windows and lab procedures, call AMH Nationwide at (877) 731-6362.
Who typically orders hair THC testing?
Hair THC testing is commonly ordered by employers, probation officers, courts, and other organizations requiring long-term drug use history. It is preferred when detection of drug use over several months is needed rather than recent or one-time use.
AMH Nationwide supports these clients by providing access to five national labs and coordinating collections at over 20,000 sites nationwide.
Contact AMH Nationwide at (877) 731-6362 to schedule or learn more about hair THC testing.
Is hair THC testing used for DOT-regulated testing?
No, hair testing is not approved for Department of Transportation (DOT) safety-sensitive drug testing. DOT requires urine testing following the federally certified urine protocol under 49 CFR Part 40.
Hair testing is used for non-DOT roles where longer detection windows are desired, but it does not meet the DOT’s regulatory standards for workplace drug testing.
Common Questions
THC can be detected in hair for up to 90 days or longer depending on hair length and individual factors. The standard sample length is 1.5 inches from the scalp, reflecting about three months of drug history.
Passive exposure to marijuana smoke is unlikely to cause a positive hair test because labs use cutoff levels designed to prevent false positives from environmental contamination.
Typically, a 1.5-inch sample of hair weighing about 100 milligrams is collected close to the scalp to provide a 90-day detection window.
Hair tests detect longer-term drug use, usually up to 90 days, whereas urine tests detect recent use within days. Both have high accuracy when processed by certified labs.
Yes, darker hair with more melanin can bind more THC metabolites, potentially leading to higher detected concentrations compared to lighter hair.
Chemical treatments such as bleaching or dyeing can degrade THC metabolites in hair, which may reduce detection sensitivity but do not guarantee a negative result.
Ready to get started?
AMH Nationwide provides the lab order and arranges collection nationwide. Every non-negative result reviewed by a certified Medical Review Officer. Call (877) 731-6362 or contact us.