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Getting to the Root of It: An Intro to Hair Drug Testing


Hair drug testing has become an increasingly common method for detecting drug use over time. As the name suggests, a small sample of hair is analysed to look for traces of drugs and their metabolites. But how does it work and what can it actually tell you?

This article explores the ins and outs of hair testing.

What Can Hair Tests Detect?

Hair tests can detect a wide range of illegal drugs, prescription medications, and alcohol use. This includes commonly abused substances like marijuana, cocaine, opiates, methamphetamine, ecstasy, and phencyclidine (PCP). Hair can also contain traces of nicotine and cotinine, chemicals indicating tobacco use.

The premise is that as these substances are ingested, small amounts get deposited in the hair follicles. As hair grows at an average rate of 0.5 inches per month, it creates a timeline of drug use.

Looking Back in Time 

How far back can a hair drug test show? One of the main advantages of hair testing is its larger detection window compared to other methods like urine or saliva analysis. While traces of drugs typically only stay in bodily fluids for a few days up to a month, how long drugs stay in your hair is far longer.

Most hair tests use a 1.5 inch hair sample, which provides an approximate 90-day window of detection. How far back a hair test can reveal depends on the length of sample tested. Each 0.5 inch represents about 30 days of growth, so a 3 inch sample could detect drug use patterns over the previous 90 to 180 days.

This allows employers, clinicians, or parents to get an overview of longer-term drug use trends. It’s important to note, however, that hair testing cannot determine exact dates/times of use or detect very recent or one-off use.

How Hair Tests Are Performed

Hair drug testing involves cutting 50-120 strands of hair from the back of the head, as close to the scalp as possible. It’s important professional collectors only take the minimum amount needed and cut from less visible locations.

The sample then gets sent to a toxicology laboratory for analysis, most often involving sophisticated techniques like GC/MS or LC/MS/MS. Technicians finely chop samples and chemically pre-treat hair to extract embedded drug residues. The resulting concentrate gets screened and any positives verified.

Alongside the chemistry, labs also consider sample validity markers like colour, texture damage, signs of chemical treatment, and how cleanly the hair was cut. Results get reviewed by certified physicians before final reporting.

Benefits and Limitations

When performed correctly, hair analysis offers a reliable way to track historical drug use trends. As hair specimens are hard to tamper with, tests have a high resistance to evasion tactics like adulterating or substituting samples. Collecting hair is also non-invasive compared to drawing blood or requiring urination.

However, critics argue results can be skewed by cosmetic hair treatments, environmental exposure, or natural hair properties. There’s also issues around variable growth rates and lack of dosage information. Like any test, hair analysis has advantages and disadvantages that require careful interpretation.

Hair testing offers a longer window of detection that can complement fluid testing. It detects a wide range of drugs and alcohol markers that get deposited in hair as it grows. How far back a test screens depends on the sample length, but approximately three months is standard. Hair testing has its pros and cons, so results require careful handling.

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