Drug testing analyses biological specimens like saliva or urine to detect the presence of illegal drugs or medications. It is used to identify drug abuse and addiction. The test results help to provide early treatment and prevent accidents. Hair drug testing accurately detects the presence of drugs and is more effective than a saliva or urine test. It allows doctors to know whether legal or prescription drugs are used in a way that they do not prescribe. It identifies whether a person has used the drug within 90 days before the test. Meanwhile, drugs identified using a hair follicle drug test are:


  • Amphetamine
  • Marijuana
  • Cocaine
  • Opioids
  • Ecstasy
  • Phencyclidine

What Is a Hair Follicle Drug Test?

In this test, hair close to the scalp is taken from different spots on the crown. It is sent to the lab for drug testing. So, all hair follicles have blood vessels and absorb nutrients from the bloodstream, and any drug present in the bloodstream is deposited inside the hair shaft. The drug test identifies the presence of metabolites of drugs in the hair shaft. Body hair is taken as a sample for testing for people with little or no hair on their heads. ELISA is a test used to identify the presence of drugs in hair shafts.

Test Results

Negative: A negative result indicates that no drug metabolites or drugs were found in the hair sample. The results show that the person has not used drugs within 90 days.

Positive: A positive test result is confirmed after 72 hours. It means that drug metabolites or drugs were found in the hair sample. A GC/MS test is done to confirm a positive result.

Inconclusive: An inconclusive test result indicates that something went wrong while testing. Hence, the person may be asked to provide another sample.

What Causes Inaccurate Results?

Contamination: Even when people have not used a drug like cocaine, the cocaine molecules bind to the hair when they are around it. Washing the hair doesn’t remove it and leads to false positives.

Hair Colour: Drug metabolites bind easily to darker hair due to melanin. As such, the test result shows false high concentrations.

Hair Treatments: Colouring, bleaching and shampooing the hair affects the drug metabolite concentration in the hair shaft. In such cases, untreated hair from other body parts is an ideal sample for the test.

Places That Require a Drug Test

  • Tests are done in workplaces to screen applicants and test employees after an issue.
  • It is done for forensic testing during criminal investigations.
  • This test is carried out in drug rehabilitation centres to check for drug abuse.

Advantages of Hair Follicle Drug Test

  • The test is highly accurate.
  • It is difficult to cheat.
  • The sample collection method is non-invasive.
  • The results show patterns of drug abuse over weeks and months.
  • Results are obtained in a short time.

A person’s hair grows one centimetre in a month, and each centimetre of hair reflects one month’s drug use. So, a 4 cm hair sample helps to assess drug usage in the past four months. Meanwhile, urine tests can detect the drug used within two to three days.

The hair drug testing results are accurate; however, the test is inappropriate for identifying recent drug use because hair takes time to grow. Hair growth rates vary for people, and the exact date of drug use cannot be determined. Meanwhile, many corporate, educational, legal and medical institutions ask people to take this test in addition to a urine test.