--- title: "How long is weed in your hair" description: "Learn how long is weed in your hair with precise THC hair test detection windows. Understand lab processes and results. Call (877) 731-6362 for info." author: "AMH Nationwide" date: "2026-08-28" tags: ["how long is weed in your hair", "how long is weed in your hair | how long is thc in your hair | how long is weed in hair | how long is thc in hair | how long thc in hair | how long weed in hair"] canonical: "https://amhnationwide.com/how-long-is-weed-in-your-hair/" last_updated: "2026-08-28" --- # How long is weed in your hair **By AMH Nationwide** | August 28, 2026 Learn how long is weed in your hair with precise THC hair test detection windows. Understand lab processes and results. Call (877) 731-6362 for info. --- How long is weed in your hair depends on hair length and usage frequency, generally detectable for up to 90 days. Hair testing detects THC metabolites embedded in the hair shaft, providing a longer detection window than urine or blood tests. AMH Nationwide routes collections through five national labs for accurate results. Call (877) 731-6362. [DETECTION WINDOW](https://amhnationwide.com/hair-follicle-drug-test-detection-window/) ## How long is weed in your hair detectable by a drug test? Weed, or THC, can typically be detected in hair samples for up to 90 days after use. Hair testing identifies THC metabolites that accumulate in the hair shaft as it grows. Since head hair grows about half an inch per month, a standard 1.5 inch sample reflects roughly three months of history. This detection window is significantly longer than [urine](https://amhnationwide.com/urine-drug-testing/) or blood testing, which usually detect THC for only days to weeks. Hair testing is preferred for long-term usage verification or legal and employment purposes. TESTING PROCESS ## What is the process for THC hair testing at AMH Nationwide? AMH Nationwide coordinates the lab order and directs clients to one of over 20,000 nationwide collection sites affiliated with five major national lab networks: [Quest Diagnostics](https://www.questdiagnostics.com/), [LabCorp](https://www.labcorp.com/), Omega Labs, United States Drug Testing Labs, and ExperTox. There is no online ordering; all test requests require contacting AMH directly. At collection, a small hair sample is taken from the head or body. The sample is sent to the lab where it undergoes screening and confirmation testing. Every non-negative result is reviewed by a certified Medical Review Officer (MRO) for accuracy and interpretation. Collection sites: 20,000+ nationwide Labs: Quest Diagnostics, LabCorp, Omega Labs, United States Drug Testing Labs, ExperTox MRO review: All non-negative screens No online ordering: Call (877) 731-6362 to schedule THC IN HAIR SCIENCE ## How does THC get into hair and what affects detection? THC enters hair primarily through the bloodstream after consumption. As hair follicles grow, THC metabolites are deposited inside the hair shaft. External contamination from smoke does not generally cause a positive result because labs wash samples before analysis. Factors influencing detection include hair color, thickness, and cosmetic treatments. Darker hair may bind more THC, while bleaching or dyeing can reduce detectable levels. Frequency and amount of use also impact metabolite concentration. THC metabolites deposit in hair from bloodstream Hair washing in labs removes external contamination Darker hair may retain more THC Chemical treatments can lower detectable THC Regular use leads to higher metabolite levels USAGE AND DETECTION ## Does one-time or infrequent use show up in hair testing? One-time or infrequent use of weed can sometimes be detected, but low metabolite levels may fall below test cutoffs. Hair tests are more reliable at detecting repeated or chronic use due to accumulation of THC metabolites over time. Because hair testing covers a longer time frame, a single use might be missed if the sample length corresponds to a period before consumption or if the amount used was very small. ## Need a THC Hair Test? Contact AMH Nationwide For accurate, federally compliant THC hair testing routed through major national labs, call (877) 731-6362 to schedule your collection or get answers. [Call (877) 731-6362](tel:+18777316362)[Contact Us](https://amhnationwide.com/contact-us/) DOT AND NON-DOT TESTING ## Is hair testing for THC accepted by DOT and other employers? For DOT-regulated safety-sensitive positions, urine testing following the federally certified [49 CFR Part 40](https://www.transportation.gov/odapc/part40) urine protocol is mandatory. Hair testing is not permitted for DOT drug tests but is used by many non-DOT employers and legal entities for longer detection windows. AMH Nationwide offers both urine and hair testing routed through [SAMHSA](https://www.samhsa.gov/workplace/drug-testing)-certified labs. Hair testing is a preferred alternative for non-DOT roles requiring extended detection of past THC use. TESTING RELIABILITY ## How reliable are THC hair test results from AMH Nationwide? AMH Nationwide uses accredited labs with strict quality controls, including SAMHSA alignment and CLIA certification. All positive or non-negative hair test results undergo review by certified Medical Review Officers who verify validity and rule out potential errors or medical explanations. This process ensures high reliability and defensibility of THC hair test results for employers, courts, and individuals. AMH Reviewed & Maintained By AMH Nationwide Customer Service AMH Nationwide is BBB A+ accredited and routes every order through Quest Diagnostics, LabCorp, Omega Labs, United States Drug Testing Labs, or ExperTox, all of which use multiple lab certification agencies and standards such as SAMHSA-aligned laboratory protocols, the ANSI National Accreditation Board for forensic testing and calibration, the College of American Pathologists (CAP), and Clinical Laboratory Improvement Amendments (CLIA). Every non-negative screen is reviewed by a certified Medical Review Officer as part of standard processing before a result is released, and chain-of-custody documentation is maintained on every collection. This page does not constitute medical or legal advice. **Last updated:** July 2026 You May Also Need [Nail Drug TestingNo head or body hair available? A 5-panel fingernail test covers a similar look-back window.Learn more →](https://amhnationwide.com/5-panel-fingernail-drug-test/)[ChildGuard: Environmental ExposureConcerned about a child or loved one? ChildGuard screens for exposure to drugs in their environment.Learn more →](https://amhnationwide.com/5-panel-hair-drug-test-environmental-exposure-childguard/)[Shorten the Detection WindowShortened options like 30 and 60 day hair panels are also available, useful when a urine test’s 1-3 day window is too short.Learn more →](https://amhnationwide.com/30-day-hair-drug-test/)[Hair ETG Alcohol TestAlso need alcohol testing? The hair ETG test screens for alcohol use, and can be added to the same collection.Learn more →](https://amhnationwide.com/etg-and-peth/) Frequently Asked Questions ## Common Questions THC can be detected in hair for up to 90 days, but one-time use may result in metabolite levels below the test cutoff, making detection less certain. No. Lab washing procedures remove external contamination, so passive exposure does not typically lead to a positive THC hair test. Yes. Darker hair can bind more THC metabolites, potentially increasing detection sensitivity compared to lighter hair. Usually about 1.5 inches of head hair is collected, representing approximately 90 days of growth and drug history. No. The DOT requires urine testing under 49 CFR Part 40. Hair testing is used for non-DOT testing purposes. Call (877) 731-6362 to arrange lab order and find a nearby collection site. AMH does not offer online ordering. Sources • [SAMHSA – Mandatory Guidelines for Federal Workplace Drug Testing Programs](https://www.samhsa.gov/workplace/drug-testing) • [U.S. DOT – 49 CFR Part 40 – Procedures for Transportation Workplace Drug and Alcohol Testing Programs](https://www.transportation.gov/odapc/part40) • [CDC – National Center for Health Statistics – Drug Use FastStats](https://www.cdc.gov/nchs/fastats/drug-use.htm) • [Quest Diagnostics – Employer Solutions, Hair Testing Methodology](https://www.questdiagnostics.com/) • [LabCorp – Occupational Testing Services](https://www.labcorp.com/) ## 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. [Call (877) 731-6362](tel:+18777316362)[Contact Us](https://amhnationwide.com/contact-us/) --- **Need a drug, alcohol, HIV or STD test?** AMH Nationwide is a national lab testing agency operating since 2004, with more than 20,000 collection sites across the United States. Hair, urine, fingernail and blood testing, panels from 5 through 19, for individuals and employers. - Call: (877) 731-6377 - Find a collection site: https://amhnationwide.com/locations/ - Full page: https://amhnationwide.com/how-long-is-weed-in-your-hair/