--- title: "How long does weed stay in your system hair sample" description: "Learn how long does weed stay in your system hair sample with expert lab testing. Accurate results reviewed by certified Medical Review Officers. Call (877) 731-6362." author: "AMH Nationwide" date: "2026-08-28" tags: ["how long does weed stay in your system hair sample"] canonical: "https://amhnationwide.com/how-long-does-weed-stay-in-your-system-hair-sample/" last_updated: "2026-08-28" --- # How long does weed stay in your system hair sample **By AMH Nationwide** | August 28, 2026 Learn how long does weed stay in your system hair sample with expert lab testing. Accurate results reviewed by certified Medical Review Officers. Call (877) 731-6362. --- How long does weed stay in your system hair sample depends on hair length and usage frequency, typically up to 90 days detection. Hair testing detects THC metabolites embedded in the hair shaft, providing a longer detection window than urine or blood. AMH Nationwide directs you to certified collection sites with results reviewed by Medical Review Officers. Call (877) 731-6362. [DETECTION WINDOW](https://amhnationwide.com/hair-follicle-drug-test-detection-window/) ## How long does weed stay in your system hair sample? Weed can be detected in a hair sample for up to 90 days after use. Hair testing identifies THC metabolites that become trapped in the hair shaft as it grows, reflecting drug use over several months. The standard hair length tested is 1.5 inches from the scalp, representing roughly a 90-day detection window. Longer hair may extend this window, while shorter hair provides a shorter detection period. TESTING PROCESS ## How is weed detected in a hair sample by the lab? AMH Nationwide routes hair samples through five national lab networks: [Quest Diagnostics](https://www.questdiagnostics.com/), [LabCorp](https://www.labcorp.com/), Omega Labs, United States Drug Testing Labs, and ExperTox. These labs use scientifically validated methods to detect THC metabolites in hair. The hair collection is done at authorized sites arranged by AMH. The sample is analyzed using immunoassay screening followed by confirmatory testing with gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS) to ensure accuracy. TEST ACCURACY ## Can hair testing for weed detect one-time or passive exposure? Hair testing is designed to detect chronic or repeated marijuana use rather than single exposures. A one-time use may not always result in a positive hair test due to the threshold levels set for THC metabolites. Passive exposure to marijuana smoke is unlikely to cause a positive hair test because the testing focuses on metabolites incorporated inside the hair shaft, not external contamination. EMPLOYER & LEGAL USE ## Who typically orders hair sample testing for weed detection? Employers, courts, [probation](https://amhnationwide.com/hair-follicle-drug-test-probation/) officers, and other legal entities commonly order hair drug testing to verify long-term marijuana use. Hair testing is preferred for its extended detection window and tamper-resistant sample. Individuals may also request hair testing for personal reasons, but AMH Nationwide requires a lab order and directs clients to collection sites; there is no option to order tests online. ## Get Accurate Hair Drug Testing for Marijuana Today To schedule a hair sample collection or discuss testing options, call AMH Nationwide at (877) 731-6362. We guide you to certified collection sites and ensure reliable lab results reviewed by Medical Review Officers. [Call (877) 731-6362](tel:+18777316362)[Contact Us](https://amhnationwide.com/contact-us/) LAB PROTOCOLS ## What happens if a hair sample tests positive for weed? Every non-negative hair test result undergoes review by a certified Medical Review Officer (MRO) to confirm the findings and rule out potential lab errors or legitimate medical explanations. AMH Nationwide’s partnered labs follow strict chain-of-custody and quality assurance protocols in compliance with [SAMHSA](https://www.samhsa.gov/workplace/drug-testing), CAP, and CLIA standards to maintain result integrity. TEST LIMITATIONS ## Are there limitations to hair testing for weed detection? Hair testing may not detect very recent marijuana use, as it takes about 5-7 days for metabolites to appear in newly grown hair. Certain hair treatments like bleaching or dyeing can reduce THC metabolite concentration, potentially affecting results. However, labs account for these factors during analysis. 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 Hair drug tests typically detect marijuana use up to 90 days because the test analyzes 1.5 inches of hair growth from the scalp, reflecting approximately three months of drug history. A single use may not always be detected due to the cutoff levels labs use to avoid false positives. Hair testing is more reliable for identifying repeated or chronic marijuana use. No. Hair tests detect THC metabolites inside the hair shaft, not external contamination. Passive smoke exposure is unlikely to produce a positive test result. Results usually take 3 to 5 business days after the lab receives the hair sample. The process includes initial screening, confirmatory testing, and MRO review. Yes. Treatments like bleaching or dyeing can reduce metabolite levels. Labs consider these factors and may note hair damage, but testing remains reliable overall. No. DOT-regulated safety-sensitive testing requires federally certified [urine](https://amhnationwide.com/urine-drug-testing/) testing under [49 CFR Part 40](https://www.transportation.gov/odapc/part40). Hair testing is used for non-DOT roles. 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-stay-in-your-system-hair-sample/