How Far Can a Hair Drug Test Go to Detect Drug Use Over Time

How far back can a hair follicle test detect drug use?

A hair follicle test can detect drug use up to approximately 90 days before the sample collection date. This is because hair grows about half an inch per month, and labs typically analyze 1.5 inches of hair closest to the scalp.

This 90-day window is much longer than urine or saliva tests, which detect recent use within days. Hair testing identifies drug metabolites embedded in the hair shaft as it grows.

How reliable is a hair drug test for detecting past drug use?

Hair drug tests are highly reliable for detecting drug metabolites accumulated over time. The sample is collected under supervised conditions at one of AMH’s 20,000+ nationwide collection sites and analyzed by certified labs including Quest Diagnostics, LabCorp, Omega Labs, United States Drug Testing Labs, and ExperTox.

All non-negative results undergo review by a certified Medical Review Officer (MRO) to verify findings and rule out possible medical explanations, ensuring accuracy and compliance with federal standards.

Are there limitations to how far a hair drug test can go?

While hair tests cover up to 90 days, they do not detect drug use beyond that timeframe because older hair is typically not collected or tested.

Also, hair treatments like bleaching or dyeing can sometimes reduce drug metabolite levels but rarely eliminate them completely. Passive exposure to drugs is unlikely to cause a positive result due to the metabolite incorporation process.

Hair tests do not detect very recent use within the last 5-7 days since it takes time for hair to grow out from the follicle.

Who typically orders hair follicle drug tests and why?

Employers, courts, probation officers, and individual clients often order hair follicle tests to verify long-term drug abstinence.

This test is preferred in situations requiring a longer detection window than urine or saliva tests, such as pre-employment screening, legal cases, or monitoring compliance with treatment programs.

How is hair collected for a drug test through AMH Nationwide?

AMH Nationwide directs test requesters to one of its 20,000+ nationwide collection sites where a trained collector cuts a small sample of hair, usually from the crown area near the scalp.

The sample is then sent to one of five national lab networks for analysis. The process follows strict chain-of-custody and testing protocols to ensure integrity and accuracy.

Is hair testing used for DOT-regulated safety-sensitive positions?

Hair drug testing is not approved for DOT-regulated safety-sensitive positions which require federally certified urine testing under 49 CFR Part 40.

However, hair testing is commonly used for non-DOT roles where a longer detection window is needed.

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