Why do drugs from passive exposure and underestimate show up differently in a hair analysis drug test?

The primary difference is the wider window of detection with hair. Cocaine, methamphetamine, opiates and PCP are rapidly excreted and usually undetectable in urine 72 hours after use. Rather than the hours or days covered by a body fluid test, a hair test covers a period of months, ensuring that a drug user cannot evade the test by simply abstaining for a few days. Additional advantages include: non-intrusive collection procedures, virtual elimination of test evasion through substitution or adulteration, and greater accuracy through test repetition capability. The combination of an increased window of detection and resistance to evasion makes hair testing far more effective than urinalysis in correctly identifying drug users.

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