--- title: "How far back does a hair sample drug test go" description: "How far back does a hair sample drug test go? Hair tests detect drug use up to 90 days prior. Call (877) 731-6362 for lab testing options." author: "AMH Nationwide" date: "2026-08-28" tags: ["how far back does a hair sample drug test go"] canonical: "https://amhnationwide.com/how-far-back-does-a-hair-sample-drug-test-go/" last_updated: "2026-08-28" --- # How far back does a hair sample drug test go **By AMH Nationwide** | August 28, 2026 How far back does a hair sample drug test go? Hair tests detect drug use up to 90 days prior. Call (877) 731-6362 for lab testing options. --- How far back does a hair sample drug test go? Hair drug tests typically detect drug use up to 90 days prior to collection. This makes hair testing ideal for employers, courts, and probation officers seeking long-term substance use history. Samples are processed through five national lab networks and reviewed by certified Medical Review Officers. Call (877) 731-6362. [DETECTION WINDOW](https://amhnationwide.com/hair-follicle-drug-test-detection-window/) ## How far back does a hair sample drug test go? A hair sample drug test can detect drug use for approximately 90 days before the sample collection date. This detection window is based on the average growth rate of head hair, about half an inch per month. Laboratories typically analyze 1.5 inches of hair closest to the scalp to capture this three-month history. This longer detection window contrasts with [urine](https://amhnationwide.com/urine-drug-testing/) or saliva tests that detect recent use, generally within days. Hair testing is preferred when a longer-term drug use pattern is needed. TESTING PROCESS ## How is a hair sample collected and tested? Hair is collected from the head close to the scalp in a small sample, usually about 100 strands weighing 50 milligrams. If head hair is unavailable, body hair may be used but has a less precise timeline. Samples are sent to one of the five national lab networks: [Quest Diagnostics](https://www.questdiagnostics.com/), [LabCorp](https://www.labcorp.com/), Omega Labs, United States Drug Testing Labs, or ExperTox. Each lab follows strict protocols for drug extraction and analysis using highly sensitive techniques like immunoassay screening followed by confirmatory gas chromatography-mass spectrometry (GC-MS). All non-negative results are reviewed by a certified Medical Review Officer (MRO) to ensure accuracy and rule out potential causes unrelated to drug use. WHO ORDERS ## Who typically orders hair sample drug tests? Hair drug tests are commonly ordered by employers for [pre-employment](https://amhnationwide.com/pre-employment-hair-testing/) screening or random testing when a longer detection window is required. Courts and [probation](https://amhnationwide.com/hair-follicle-drug-test-probation/) agencies use hair testing to monitor compliance over months. Individuals may also request hair tests for personal monitoring or legal purposes. Because hair testing is not accepted for DOT-regulated safety-sensitive positions, those tests use federally certified urine protocols instead. PASSIVE EXPOSURE ## Can passive exposure to drugs affect hair sample drug test results? Passive exposure to drugs, such as being in a room with drug smoke, is unlikely to produce a positive hair drug test. The testing process targets drug metabolites incorporated into the hair shaft from bloodstream exposure, not external contamination. Laboratories apply wash procedures to hair samples to remove surface contaminants before analysis, reducing false positives from environmental exposure. ## Need a Hair Sample Drug Test? AMH Nationwide coordinates hair drug testing through national labs with certified Medical Review Officer review. Contact us to schedule a collection at one of 20,000+ nationwide sites. Call (877) 731-6362. [Call (877) 731-6362](tel:+18777316362)[Contact Us](https://amhnationwide.com/contact-us/) ONE-TIME USE ## Can a hair sample drug test detect one-time drug use? Hair testing can detect single drug use incidents if enough drug is incorporated into the hair. However, very occasional or low-dose use might be below the test’s sensitivity threshold. Because hair grows slowly, the timing of use relative to hair length sampled affects detection. If the drug use occurred less than 7 days before collection, it may not yet appear in the hair tested. TEST RELIABILITY ## How reliable is hair sample drug testing compared to other methods? Hair drug testing provides a reliable, longer-term view of drug use compared to urine or saliva tests that detect recent use only. The use of five national lab networks and review by certified Medical Review Officers ensures high accuracy and reduces false positives or negatives. Hair testing is less invasive and harder to adulterate than urine tests, making it ideal for legal and employment settings requiring documented substance use history. 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 Hair grows approximately half an inch per month. Labs typically test 1.5 inches of hair from the scalp, representing about 90 days of drug use history. Hair testing can detect many common drugs including cocaine, marijuana, opiates, methamphetamine, and PCP. Detection depends on the panel ordered and drug incorporation into hair. No. DOT-regulated safety-sensitive testing requires federally certified urine testing under [49 CFR Part 40](https://www.transportation.gov/odapc/part40). Hair testing is used for non-DOT roles. Hair treatments like bleaching or dyeing can reduce drug concentration in hair but do not guarantee a negative result. Labs account for such factors during analysis. Pricing varies by drug panel and detection window. Contact AMH Nationwide at (877) 731-6362 for a quote. Hair testing is difficult to adulterate due to laboratory wash steps and metabolite detection. Attempting to cheat can lead to test invalidation or legal consequences. 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-far-back-does-a-hair-sample-drug-test-go/