In this article, we discuss how hair follicle drug tests work, how to use a home kit, and what the results mean. We also cover the accuracy and cost of testing, whether people without hair can still provide a sample, and how hair follicle tests compare to traditional urine-based drug tests.
What is a hair follicle drug test?
A hair follicle drug test can detect marijuana and cocaine use.
A hair follicle drug test can determine patterns of illicit drug use or prescription medication misuse over a certain period — this is typically 3 months for hair samples that come from a person's head.
Testers can use hair follicle tests to check for a specific drug, or they can test a single hair sample for several different drugs or drug classes.
A hair follicle test can detect:
- amphetamines, including methamphetamine, MDMA (ecstasy), and MDEA (eve)
- opiates, such as heroin, codeine, and morphine
- phencyclidine (PCP)
Why is it necessary?
A person may need to undergo drug testing for employment, legal, or medical purposes.
Some companies require potential employees to take a drug test as part of their application process, particularly for jobs that carry a high risk of injury. Employers may also carry out random drug testing for current employees, or they may request drug tests following serious accidents or incidents.
In the United States, drug testing laws vary from state to state. Some states prohibit employers from drug testing their employees on a random basis. In these states, an employer must provide evidence that supports their decision to test a particular employee.
Courts may require drug testing for individuals on probation or during child custody, adoption, and domestic violence cases.
Healthcare providers sometimes request testing for people at risk of drug or alcohol misuse.
However, it is important to note that drug testing generally requires a person's written consent.
What happens during the test?
A hair follicle drug test can take place in a healthcare setting, a workplace, or at home.
During the test, the tester will remove a small hair sample close to a person's scalp and send it to a laboratory for overnight testing.
Prescription medications and certain foods, such as poppy seeds, may contain compounds that might lead to false positive results. Hair samples undergo a two-step process to ensure accurate test results.
The first step involves an enzyme-linked immunosorbent assay (ELISA) test, which is a rapid screening method.
If the ELISA test produces a positive result for a particular substance, a technician will retest the hair sample using confirmatory chromatographic testing, such as gas chromatography-mass spectrometry (GC-MS), to rule out false positives.
How to use a home test
Once a person has provided their sample, they should post the at-home hair follicle testing kit.
People can order at-home hair follicle testing kits through online providers. These kits include an instruction manual and a pre-paid envelop for mailing the hair sample to the laboratory.
How to use a home test:
- Carefully read the instruction manual that comes with the kit.
- Collect a hair sample according to the manufacturer's directions.
- Wrap the hair sample in a piece of foil.
- Place the foil-wrapped hair in the provided envelope.
- Mail the envelope to the laboratory for analysis.
A person can usually access their test results by calling a toll-free number or going online and using the unique identification number that comes with the kit.
What do the results mean?
The results of a hair follicle drug test can be negative, positive, or inconclusive:
A negative result means that the laboratory did not detect the presence of any drug metabolites in the hair sample, or after having a positive ELISA screening, the laboratory was unable to confirm the results with GC-MS.
Hair samples that produce a positive result for ELISA testing will undergo a second test, such as GC-MS. A positive result with confirmatory testing means that the laboratory confirmed the presence of specific drug metabolites in the person's hair sample.
If the hair sample is contaminated or something goes wrong during the testing, the laboratory may declare the result to be inconclusive. In these cases, a person may need to provide a new hair sample to the laboratory.
How accurate is it?
Hair follicle drug tests can determine whether a person has been using certain substances within the past 3 months. However, these tests cannot pinpoint the exact date of drug use because hair growth rates can vary widely among different people.
Although hair samples undergo a two-step testing process, they are not 100 percent accurate.
Factors that can affect the concentration of drug metabolites present in a hair sample include:
- the structure of drug compounds
- the quantity of drugs a person has consumed
- how much a person sweats
- the amount of melanin (dark hair pigment) in a person's hair — certain drugs bind more readily to melanin
- bleaching or coloring the hair
The use of typical styling products and shampoos should not affect the test results.
In 2015, researchers at the Friends Research Institute in Baltimore, Maryland, conducted a study examining the effectiveness of hair follicle drug tests.
The researchers compared self-reported drug use with hair follicle test results from 360 adults at risk for moderate drug use.
According to the results of the study, hair follicle drug testing correctly identified:
- 52.3 percent of people who reported recent marijuana use
- 65.2 percent of people who reported recent cocaine use
- 24.2 percent of people who reported recent amphetamine use
- 2.9 percent of people who reported recent opioid use
In a 2017 study, researchers compared the results of hair follicle drug tests with self-reported drug use from 3643 participants. Compared to the researcher's expectations, the test results produced fewer potential false positives, but more potential false negatives.
Due to the study results, the researchers concluded that hair follicle tests do not provide reliable information regarding drug use in the general population.
There is a range of different home kits for hair follicle drug testing on the market. People can purchase these kits either directly through the company's website or from pharmacies and online.
Some drug testing kits are available for a flat fee that includes laboratory testing and all shipping costs. For other kits, a person pays a basic price for the actual kit and an additional amount depending on which drugs the laboratory tests for.
Packages that include the home kit and testing for 12 different drugs typically cost less than $100.
Employers who wish to drug test their employees must cover all the costs of taking the test, taking into account the person's time.
Some health insurance companies cover the cost of hair follicle drug testing for medical purposes.
What if a person has no hair on their head?
Hair samples can come from the armpit or face, so people who do not have hair on their heads can still take a hair follicle drug test. However, a person's hair must be at least 0.5–1.5 inches in length. A person with shorter hair may need to supply more hair for the sample.
People who shave their entire bodies may not be able to provide a usable sample of hair.
Hair follicle test vs. urine test
Hair samples are less vulnerable to tampering than urine samples.
Hair follicle tests provide a much larger window of detection than urine tests.
According to a 2017 study, urine tests have a detection window of up to 10 hours to about 1 week for most drugs except marijuana, which can remain present in a person's urine for up to 30 days.
Hair follicle tests can detect drug use for up to 3 months before testing for hair samples that come from a person's scalp.
Urine tests can detect more recent drug use, while hair follicle tests can identify regular, long-term drug use.
It is also easier for a person to tamper with a urine sample than it is a hair sample, which may give hair follicle tests an advantage over urine tests when a person takes the test in a laboratory setting.
Although most drug screening still involves testing urine samples, hair follicle tests can help identify individuals who participate in regular, long-term drug use.
Some corporate, legal, medical, and educational institutions have turned to hair follicle drug tests as a complementary approach to traditional urine-based testing.
There is a growing interest in hair follicle testing because drug metabolites can remain present in hair from a person's scalp for up to 3 months.
Hair follicle testing involves an up to two-step testing process to reduce the risk of false positive results.
People currently taking prescription medications should share this information with their employer or test administrator. Hair follicle tests can detect the presence of some prescription medications, which can lead to a false-positive result.