--- title: "How long does weed last in hair" description: "Discover how long does weed last in hair with precise THC detection windows. Learn about hair drug testing from certified labs. Call (877) 731-6362 to start." author: "AMH Nationwide" date: "2026-08-28" tags: ["how long does weed last in hair", "how long does weed last in hair | how long does thc last in hair"] canonical: "https://amhnationwide.com/how-long-does-weed-last-in-hair/" last_updated: "2026-08-28" --- # How long does weed last in hair **By AMH Nationwide** | August 28, 2026 Discover how long does weed last in hair with precise THC detection windows. Learn about hair drug testing from certified labs. Call (877) 731-6362 to start. --- How long does weed last in hair depends on the detection window of the hair follicle test, which can detect THC up to 90 days after use. This test analyzes hair samples collected at certified labs, ensuring accurate results reviewed by Medical Review Officers. Call (877) 731-6362 to schedule your collection. [DETECTION WINDOW](https://amhnationwide.com/hair-follicle-drug-test-detection-window/) ## How long does weed last in hair after use? Weed, or THC, can be detected in hair samples for up to 90 days after consumption. Hair drug testing analyzes the metabolites of THC that are deposited in the hair shaft as it grows. Because hair grows approximately 0.5 inches per month, a standard 1.5-inch hair sample represents roughly a 90-day detection window. This makes hair testing useful for identifying past marijuana use over a longer period compared to [urine](https://amhnationwide.com/urine-drug-testing/) or saliva tests. Detection window: Up to 90 days Hair growth rate: About 0.5 inches per month Sample length: Standard 1.5 inches for 3 months of history Detection beyond 90 days is uncommon because hair segments grow out and are cut off. However, the exact detection time can vary based on individual hair growth rates and testing protocols. TESTING PROCESS ## What is the hair drug test process for detecting THC? Hair drug testing for THC involves collecting a small hair sample from the scalp, typically from the crown area. The sample is then sent to one of AMH Nationwide’s five national lab networks—[Quest Diagnostics](https://www.questdiagnostics.com/), [LabCorp](https://www.labcorp.com/), Omega Labs, United States Drug Testing Labs, or ExperTox—for analysis. The labs test for THC metabolites incorporated into the hair shaft. Every non-negative result undergoes review by a certified Medical Review Officer (MRO) to confirm accuracy and rule out potential false positives. Sample collection: Small hair strand from scalp Lab networks: Quest Diagnostics, LabCorp, Omega Labs, United States Drug Testing Labs, ExperTox Result review: Certified Medical Review Officer AMH Nationwide directs the requester to a collection site; there is no online ordering. Contact us at (877) 731-6362 to arrange testing. THC DETECTION DETAILS ## How long does THC last in hair compared to other testing methods? THC detection time in hair is significantly longer than in urine or saliva. Urine tests typically detect THC from 3 to 30 days depending on usage frequency, while saliva tests detect recent use within hours to days. Hair testing can detect THC metabolites for up to 90 days, providing a longer retrospective window. This makes hair testing suitable for employers, courts, or [probation](https://amhnationwide.com/hair-follicle-drug-test-probation/) officers who need a longer-term drug use history. | Test Type | Typical THC Detection Window | | --- | --- | | Hair Test | Up to 90 days | | Urine Test | 3 to 30 days | | Saliva Test | Hours to a few days | ONE-TIME USE & PASSIVE EXPOSURE ## Can one-time use or passive exposure affect hair test results? A single use of weed may be detected in hair if the THC metabolites are deposited in the hair shaft. However, detection depends on the amount consumed and hair growth timing. Passive exposure to marijuana smoke is unlikely to cause a positive hair test because the test detects metabolites from ingestion, not external contamination. Labs use wash procedures to remove external contaminants. The review by a Medical Review Officer further validates positive results to minimize false positives. One-time use: Possible detection depending on amount and timing Passive exposure: Unlikely to cause positive results Lab wash procedures remove external contamination MRO reviews all positives to confirm validity ## Schedule Your Hair Drug Test for Weed Today Contact AMH Nationwide at (877) 731-6362 to arrange hair testing with certified labs and Medical Review Officer review. Get accurate THC detection up to 90 days. [Call (877) 731-6362](tel:+18777316362)[Contact Us](https://amhnationwide.com/contact-us/) DOT & NON-DOT TESTING ## Is hair testing for weed used in DOT-regulated safety-sensitive roles? Hair testing for THC is not used for Department of Transportation (DOT) regulated safety-sensitive positions. DOT requires urine testing following the federally certified urine protocol under [49 CFR Part 40](https://www.transportation.gov/odapc/part40). Hair testing is accepted for non-DOT roles to provide a longer detection window. Employers who require DOT testing must follow the urine test regulations, while hair testing can be used for other employment or legal purposes. DOT testing: Urine test only per 49 CFR Part 40 Hair test: Used for non-DOT roles AMH provides DOT urine testing and non-DOT hair testing separately ORDERING & COST ## How do I get a hair drug test for weed and what does it cost? To get a hair drug test for weed through AMH Nationwide, you must call (877) 731-6362 to arrange a lab order and be directed to a nearby collection site. AMH does not provide online ordering. Pricing varies depending on the test panel and detection window required. Call to request a personalized quote based on your testing needs. All tests are processed at national labs with certified Medical Review Officer oversight for reliable results. 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 Typically, a 1.5-inch hair sample weighing about 100 milligrams is collected from the scalp to provide a 90-day detection window for THC metabolites. Hair treatments like dyeing or bleaching may reduce THC metabolite levels, but labs have methods to detect and account for treated hair to ensure accurate results. Hair testing provides a longer detection window and is less susceptible to adulteration, making it more reliable for detecting past marijuana use over months compared to urine testing. Results typically take 3 to 5 business days after the lab receives the hair sample. Time may vary depending on the lab and test panel. Hair drug testing can technically be performed on children, but testing minors usually requires legal consent and clear justification due to privacy and ethical considerations. No, DOT regulations require urine testing for marijuana. AMH provides hair testing for non-DOT purposes only, following all federal guidelines. 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-last-in-hair/