--- title: "How long does weed show up in a hair test" description: "How long does weed show up in a hair test? Hair testing detects THC for up to 90 days. For precise lab testing with certified review, call (877) 731-6362." author: "AMH Nationwide" date: "2026-08-28" tags: ["how long does weed show up in a hair test", "how long does weed show up in a hair test | how long does pot show up in hair test"] canonical: "https://amhnationwide.com/how-long-does-weed-show-up-in-a-hair-test/" last_updated: "2026-08-28" --- # How long does weed show up in a hair test **By AMH Nationwide** | August 28, 2026 How long does weed show up in a hair test? Hair testing detects THC for up to 90 days. For precise lab testing with certified review, call (877) 731-6362. --- How long does weed show up in a hair test? Hair follicle tests detect THC exposure for up to 90 days after use by analyzing hair strands. This method offers a longer detection window compared to urine or saliva tests. AMH Nationwide routes collections through five national labs and ensures certified Medical Review Officer oversight. Call (877) 731-6362. [DETECTION WINDOW](https://amhnationwide.com/hair-follicle-drug-test-detection-window/) ## How long does weed show up in a hair test? Weed, or THC, can be detected in hair samples for up to 90 days after use. Hair testing measures the presence of THC metabolites embedded in the hair shaft as it grows. Because hair grows approximately half an inch per month, a standard 1.5-inch hair sample can provide a three-month usage history. This detection window is significantly longer than [urine](https://amhnationwide.com/urine-drug-testing/) or saliva tests, which typically detect THC for up to a week or two depending on usage frequency. TESTING PROCESS ## What is the process for collecting and testing hair for weed? AMH Nationwide directs clients to collection sites within its network of five national labs: [Quest Diagnostics](https://www.questdiagnostics.com/), [LabCorp](https://www.labcorp.com/), Omega Labs, United States Drug Testing Labs, and ExperTox. A small hair sample, usually from the crown of the head, is collected and sent to the lab for analysis. The testing process involves extracting and measuring THC metabolites from the hair using sensitive laboratory instrumentation. Every non-negative result undergoes review by a certified Medical Review Officer to confirm findings and evaluate possible alternative explanations. USAGE AND DETECTION ## Does one-time or occasional use affect how long pot shows up in a hair test? One-time or occasional marijuana use can still be detected in hair for up to 90 days, but the concentration of THC metabolites is typically lower than that of frequent users. Hair testing is sensitive enough to detect even low-level exposure, although very minimal or passive exposure may sometimes yield inconclusive results. Because hair testing identifies drug metabolites deposited in the hair shaft, it reflects actual ingestion rather than environmental contamination. PASSIVE EXPOSURE ## Can passive exposure to weed cause a positive hair test? Passive exposure to marijuana smoke is unlikely to cause a positive hair test result. Hair testing targets metabolites formed inside the body after THC ingestion, not THC present on the hair surface. Labs wash hair samples thoroughly to remove external contaminants before analysis. Therefore, incidental or secondhand marijuana smoke exposure does not usually result in a positive hair test. ## Schedule Your Hair Drug Test Today For accurate detection of weed in hair samples with certified lab review, call (877) 731-6362 to find a collection site near you. [Call (877) 731-6362](tel:+18777316362)[Contact Us](https://amhnationwide.com/contact-us/) COMPARISON ## How does hair testing for weed compare to other testing methods? Hair testing offers the longest detection window among common drug tests. Here is a comparison: | Test Type | THC Detection Window | | --- | --- | | Hair Test | Up to 90 days | | Urine Test | 1 to 30 days depending on use | | Saliva Test | Up to 48 hours | | Blood Test | Up to 24 hours | This makes hair testing suitable for employers, courts, and [probation](https://amhnationwide.com/hair-follicle-drug-test-probation/) authorities requiring long-term drug use history. DOT AND NON-DOT ## Is hair testing used for DOT-regulated drug testing? Hair testing is not accepted for Department of Transportation (DOT) safety-sensitive drug testing roles. DOT regulations require federally certified urine testing under [49 CFR Part 40](https://www.transportation.gov/odapc/part40). However, hair testing is commonly used for non-DOT employment screening and other contexts where a long detection window is desired. PRICING AND ORDERS ## How do I get a hair test for weed through AMH Nationwide? AMH Nationwide does not provide online ordering. To arrange hair drug testing, call (877) 731-6362 to discuss your needs. Pricing varies based on the test panel and detection window required. You will be directed to a nearby collection site within the network of five national laboratories. After collection, samples are analyzed and results reviewed by a certified Medical Review Officer. 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](https://www.samhsa.gov/workplace/drug-testing)-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 A hair test can detect marijuana use for up to 90 days by analyzing THC metabolites in hair strands. Yes, even a single use can be detected, though the concentration of metabolites will be lower than with frequent use. No, washing hair does not remove THC metabolites embedded inside the hair shaft, which labs test for after thorough cleaning. Passive exposure is unlikely to cause a positive result because hair tests measure metabolites formed inside the body. No, DOT-regulated testing requires federally certified urine testing; hair tests are used for non-DOT purposes. Call (877) 731-6362 to schedule a hair test and be directed to a collection site within our national lab network. 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-does-weed-show-up-in-a-hair-test/