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8 minutes
20 Jul 2023

How accurate is hair drug testing?

Hair drug testing is an effective way to establish an individual’s long term drug use. The test provides an effective window of drug detection of up to 6 months. In this article, we will look at how accurate hair drug testing is.

Head hair drug testing medium

How does hair drug testing work?

When consumed, drugs produce specific chemical markers in the body called metabolites. Drugs and metabolites pass into hair, which can act as a record of a person’s drug use. Their presence means we can analyse hair samples and determine if a drug was ingested by the individual. In addition, the analysis can distinguish between actual drug use rather than the result of external contamination. For example, the person being in the presence of someone else smoking cannabis.

Head hair typically grows at about one centimetre per month. Body hair grows at a similar rate but can be subject to ‘resting’ phases when hair growth slows or stops altogether. As a result, head hair provides a more reliable and accurate method of testing for a specific timescale. So, when tested, each centimetre of head hair is approximately equal to one month’s history of drug use. Therefore, hair drug testing is an accurate method of analysis and can provide a long window of effective drug detection for up to 6 months.

Furthermore, our hair drug testing service is a UKAS 17025 accredited method of testing. As a result, it is the drug test of choice for legal matters in UK courts that require evidence of drug use, or non-use, over long time periods.

Other factors that can affect the accuracy of a hair drug test

Hair drug testing sample collection

If a court orders a hair drug test to assess drug use in the past 4 months, then 4 cm of hair will be analysed. Therefore, the collection of the hair sample plays a key part in the process. Our certified sample collection officers follow strict chain of custody procedures. This includes specific instructions regarding the length of hair sample required for the period of analysis. If there are any differences in this, the collection officer will communicate any discrepancies to Crystal Health Group immediately. However, the collection officer will not cut head hair to length, this can only be done at the laboratory.

At the appointment, head hair samples will be cut as close to the scalp as possible, and the whole length of hair will be sent to the laboratory. In addition, our procedures provide detailed instructions to collection officers regarding sufficient sample for analysis at the lab. So, in effect, the accuracy of hair drug testing also depends on the information provided by our clients at the start of the booking process.

Hair drug testing detection window

Head hair takes approximately 7 days to grow out of the scalp. This is also the minimum detection time frame for the hair drug test. As a result, hair testing may need to be performed with a shorter detection drug testing method, such as urine drug testing, to cover this 7-day period.

Hair drug testing using body hair

Body hair can be collected from only certain parts of the body. As mentioned, due to differences in hair growth rate, there are testing limitations for body hair. These include:

  • Unable to segment body hair samples for a month-by-month analysis overview.
  • Due to major differences in body hair growth rate to hair, an additional time frame is added to the period of analysis requested. As a result, 1 cm of body hair will be reported as 1 month + 90 days.
  • Body hair is collected by weight, unlike head hair, which is collected by length.
  • Certain types of body hair are not suitable for testing.

Despite, the limitations, our Clinical Advisor team will be happy to talk you through the details and provide alternative options where possible.

Do hair treatments affect hair drug testing results?

Certain hair treatments can potentially impact hair drug test accuracy. The chemicals used in some hair treatments can damage the hair shaft and alter the concentration of the drug. As a result, during the sample collection appointment, clients must disclose hair treatments such as perming, straightening, bleaching, and dyeing that have been applied during the timeframe of analysis. This information is considered by the scientists at the laboratory before analysis commences. In addition, the hair sample goes through a cleaning regimen in the laboratory to minimise the risk of any contaminants.

Does medication affect hair drug testing results?

Like all other drug testing methods, full disclosure of medication taken during the timeframe of analysis is required. This will be requested at the sample collection appointment. From this information, the scientists performing the analysis can identify and distinguish between metabolites of different drug groups.

Do pregnancy hormones or menopause affect hair drug test results?

In certain circumstances, hormones can affect hair growth rates. As a result, this could have an impact on the time period shown in test results, but it would not affect the accuracy of the result.

Does hair colour affect hair drug test results?

Even with the same level of drug use, Individuals with naturally dark hair will carry more evidence of drug in their hair than people with naturally lighter hair. The more melanin there is in the hair, the more the drug will be bound into it. However, this is something that would be observed and recorded at the sample collection appointment.

Hair and blood alcohol testing in lab

What are the disadvantages of hair drug testing?

In all, hair drug testing provides many advantages as detailed above. However, there are disadvantages to the method that we make our clients aware of, these are:

  • Hair drug testing cannot precisely determine the quantity of substances used by an individual.
  • Hair drug testing does not provide specific times and dates that drug use took place.
  • For a heavy drug user, it can take three to four months for traces of a substance to disappear from new hair. As such, it may be necessary to retest an individual after three to four months to prove they have finished using a substance altogether.
  • Due to hair growth rate above the scalp and skin, hair samples cannot indicate substance use less than 7 days after consumption.
  • Detection periods are based on approximate hair growth rates, so they are always an approximation. This is especially true for certain hair types such as afro hair, which grows slower.

Expert Witness Reports

We will provide a standard laboratory report of the test results in all cases. However, also available at an additional cost is an Expert Witness Report. This report will provide much more detail regarding the results, including any impacts of hair treatments applied or medication taken. To find out more about the Expert Witness Report, call and speak to our Clinical Advisor team.

Hair drug testing is still the legal testing choice for courts in the UK

The advantages of hair drug testing far outweigh any disadvantages. As a result, it is still the testing choice for legal matters that require evidence of long-term drug use in UK courts.

We work with many solicitors, social service agencies and directly with the UK Government in providing hair drug testing for individuals and employees throughout the country. In addition, we provide the hair drug testing service direct to private individuals. Call and speak to our Clinical Advisor team today to discuss your requirements.