A hair follicle drug test reveals a roughly 90-day history of drug use — far longer than the days-long window of urine. It is the tool of choice when you need to see a pattern of use rather than a single recent exposure.
How the detection window works
As hair grows, drug metabolites are deposited in the shaft. A standard 1.5-inch sample from the scalp reflects about 90 days. Because it cannot be beaten by short-term abstinence, hair is popular for pre-employment and for-cause testing.
Hair vs. urine
Urine catches recent use (typically 1–4 days, longer for chronic THC) and is required for DOT. Hair catches longer-term patterns but not last-night use. Many programs pair a urine test for recency with hair for history.
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Common questions
How far back does a hair drug test go?
A standard scalp sample reflects roughly the previous 90 days of use.
Can you cheat a hair follicle test?
Short-term abstinence and most detox shampoos do not reliably defeat a lab-confirmed hair test, which makes it a robust choice.
Is hair testing DOT-approved?
No. DOT currently requires urine collection; hair is used for non-DOT and pre-employment programs.